open coil duct heaters

Transcription

Page 1 - GENERAL INFORMATION
Pneumatic Electric Switches
SCR (Solid State Devices)
Three Types Secondary (back-up) Systems
A - INTRODUCTION
1 - GENERAL DESCRIPTION
A Duct Heater is a self contained heater designed to be
installed in the field in an air stream of a duct system,
external to the air moving unit. It is designed to be
installed in a duct where an adequate flow of air from a
separate, interlocked fan or blower system is insured.
Such a heater may be located in a main supply duct of a
warm air heating system, in one of the branch ducts, or
used as a room heater, at the end of a branch duct.
In this catalogue, pricing and detailed data are
given regarding application and usage of the
various required and optional equipment.
4 - FLEXIBLE CUSTOM DESIGN
Inducto Duct Heaters are listed by the
Underwriter's
Laboratories
Label
Service
Department (UL Reference Number E33694)
ranging from five hundred watts to one million
watts, to fit ducts from a minimum of six inch height
x ten inch width to a maximum of eighty inches
height x twenty feet in width. This range makes the
duct heater the most versatile type of heating
system.
Inducto Duct Heaters are approved for zero
clearance to combustible surfaces, and meet all UL,
and 1975 National Electrical Code requirements.
Heaters are available for 120, 208, 240, 277, 480,
550, and 600 volt electrical rating, single or three
phase with control voltages of 24, 120. 208, 240 or
277 volts. Inducto Duct Heaters are packaged
units, completely wired for simple connection to the
power supply system. With the cover removed. line
terminals are completely exposed in a large
terminal box. Conduit knockouts and detailed wiring
diagrams are included in each unit.
Electric Duct heaters are an ideal answer for the heating
system designer, because of electricity's inherent
cleanliness as a fuel, their adaptability for use with other
comfort conditioning components, such as humidifiers,
de-humidifiers, electronic filters and heat pumps, and
their flexibility for use with a variety of control systems to
maintain the precise temperature desired. Markel has
one series of Inducto Duct Heaters to accommodate all
applications.
Series HF custom designed flange and insert
heaters.
This series has built-in primary and alternate types
of secondary over-temperature safety protection to
meet the 1975 National Electrical Code, and UL
requirements.
2-ADVANTAGES Open Coil Inducto
Duct Heaters:
Patent Module Design
Clean Heat
Double Safety Protection
Low Cost Factor
UL Listed
Instant Heat
Solid Cover for Dust Elimination
Custom Design
Insulated Control Panel (Standard)
Low Static Pressure Drop
B - TYPICAL APPLICATIONS
1 - Prime Heating: Inducto Heaters are supplying
prime heat in thousands of installations throughout
the United States and foreign countries. They are
used to heat all types of industrial and commercial
buildings, schools, hospitals, churches, residences,
and for all types of remodeling.
2 - Air Handling Equipment: Manufacturers of
cooling and air handling equipment have found
electric heating coils to be a valuable addition to
their air handling units. Inducto Heating Coils are
built to replace and fit into space provided for other
types of heating coils. Usually no re-design or
alteration of present equipment is necessary.
3 - Heat Pumps: Inducto Heaters are used as
supplementary heat with heat pumps. When
outside temperatures drop below the efficiency
range of the heat pump, the heating coils provide
the necessary additional heat.
3 - OPTIONAL EQUIPMENT
HF series are available with the following optional
equipment:
Built-in or Remote:
Magnetic Controlling Contactors Step-down
Transformers for control voltage
supply
Fuses for over-current protection Circuit
Breakers for over-current protection Time
Delays Mercury Contactors Indicator Lights
Disconnect Switch Pilot Switches
4 • Zoned Application: Where there is considerable
heat gain or loss variation in different locations
throughout a building, small blast coil heaters are
actuated to compensate and prevent over-cooling.
SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICE
2
Page 2 - CONSTRUCTION
A - FRAME
FIGURE
2
NOTE: 'OH' can apply to overhang on either side of heater
FIGURE 1
The terminal compartment extends beyond the
element enclosure at least 1/2 inch on all sides
so that it will cover the rough opening in the
duct. When additional space is required for
built-in
components
the
terminal
box
is
extended on the air inlet side as standard, or
leaving air side either up or down if specified.
The "A" dimension can be extended as an
overhang when specified.
1 - Insert Heaters are the most generally used
type because of the ease of installation in the
duct system. The heating element enclosure is
inserted in the air stream through a hole cut in
the side of the duct, and is secured by means of
screws applied from within the terminal box.
******
********
FIGURE 4
The flanged element enclosure and the terminal
compartment are flush on the air outlet side.
When "M" dimension exceeds "B" dimension,
the overhang will be on the air inlet side, as
standard, or leaving air side either up or down if
specified. The "A" dimension can be extended
as an overhang to provide space for components
when specified.
2 - Flanged Heaters are custom designed to be
installed as an integral part of the duct system.
The inside of the flange d frame is the same
dimensions as the air duct, allowing for mating
with, and securing to the duct flanges. A one
inch flange is supplied as standard, unless
otherwise specified.
3
CONSTRUCTION . Page 3
3 - Internally Insulated Duct Applications:
4 - Bottom Terminal Box Heaters: Inducto
Internally Insulated Ducts can affect the
Heaters are specially designed to accommodate
operation of insert and flanged duct heaters and
installations where side mounting is not possible.
therefore, must be specified so that the
Since the resistance element wire must be strung
following design factors can be employed which
horizontally the safety controls are located in
will allow the air stream to pass over the limit
the side terminal compartment. Other controls
controls and all elements.
except mercury contactors and fusing are
located in bottom control box. Heaters limited
to 60 KW max. Remote fusing required for all
heaters over 48 Amps. Pricing under Optional
Pricing Section.
INSERT TYPE
The element enclosure is reduced in size enough
to allow the entire face of the control box to be
recessed into the duct to the depth of the
insulation.
An angle is installed on all four sides of the
terminal compartment to seal the opening and
provide a mounting means.
FLANGE TYPE
FIGURE 7 - Bottom Terminal Box
5 - Dust Proof Terminal Box Cover: Inducto
Heaters are available with a dust tight control
box cover where dirt problems could affect the
life expectancy of the controls. Pricing found
under Optional Pricing.
6 - Multiple Heaters in a Single Duct: Inducto
Duct Heaters are designed as single units in all
applications except where height dimension
exceeds 80". Heaters above 80" will be
furnished in two or more flanged sections for
stacking one on top of the other, for simplifying
shipping and field installation. A special foot
design is furnished with these flange units for
easy mounting when stacked. Automatic
A deeper flange is required so that the inside of
the flanged housing is flush with the surface of
the insulation and the face of the terminal
compartment is recessed to the depth of the
insulation.
FIGURE 8 - Multiple Heaters in a single duct.
4
Page 4 - CONSTRUCTION
resetting temperature limits are furnished in
each heater section, with provisions for wiring
them in series in the field. Built-in accessories,
such as contactors, and fusing, are also available.
Separate power lines are required for each
section.
When preferred, heaters with a long "W"
dimension can be divided into two separate units
and one installed from each side of the duct.
B - DIMENSIONAL DATA
The HF series terminal compartment depth "E"
is normally 4 1/2", however it may be increased
when necessary. The "H" and "W" dimensions
are the actual duct height and width. "C" and
"M" dimensions depend on several factors and
must be calculated by the factory engineering
department, however where conditions limit the
size this must be specified.
The HF series compartment has a solid cover
that is hinged on the top or otherwise, also a
latch is provided. A support bridge is installed
on the bottom of the element enclosure on all
heaters when "W" dimension exceeds two (2)
feet. (See figure 1, 2 and 3).
FIGURE 9-Typical Insert Heater
FIGURE 11 - Bottom Terminal Box
C - CORROSION PROTECTION
Inducto Duct Heaters are constructed of the
highest grade galvanized steel
(standard),
aluminized
(optional).
All
other
metal
components
are
either
zinc
plated
or
constructed of stainless steel. This type of
protection gives longer life and prevents damage
by moisture from cooling systems.
D-INSULATION
Each heater is manufactured with a 1/2"
fiberglass board insulation between the control
box and the duct area. This type of insulation
gives maximum protection against moisture
condensation as well as thermal insulation. In
installations where noise is a factor, such as high
rise apartments, this type of insulation absorbs
part of the air movement sound.
E- HEATING ELEMENT
1 - Open Coil Type: The open coil
element offers many advantages over the
sheath type. One of the greatest assets is
its longer life. The open coil releases its
heat
directly
into
the
air
stream,
transferring
its energy faster, and
therefore
operating
at
a
cooler
temperature. The sheath type element
must release its energy through an
insulation and the metal outside sheath.
Due
to
this
slower
transfer,
life
expectancy
is
reduced
and
service
requirements increased. In some cases,
the insulation may contain voids, in
which case, the conduction is reduced
creating possible burn-outs. The open
coil gives greater adaptability in design
and lower pressure drop across the unit.
This feature can help the systems
designer maintain a lower static pressure,
and thereby reduce the air handling
power requirements, design and system
costs.
FIGURE 10-Typical Flanged Heater
5
CONSTRUCTION - Page 5
G - ELEMENT TERMINATION
The coil is mechanically connected to the high
temperature No. 10 stainless steel terminal screw
by means of a loop of element wire being
sandwiched between two stainless steel washers.
Since a large area of element wire is used in
making the connection, burn-outs due to nicked
wire at the connection are minimized. The
terminal is insulated by a two piece mating male
and female ceramic bushing.
The low mass coil releases heat
immediately
after
being
energized
and
cools
quickly
after
being
de-energized.
The low thermal inertia results in more
precise temperature control.
2 - Element Construction: The Inducto Duct
Heater elements are constructed of high grade
resistance wire. Each element is coiled to the
customer's wattage specification in our plant,
assuring high quality elements with a closely
controlled resistance. Each element is checked
when produced, and again upon installation in
the heater.
Inducto heating element coils are designed for
low watt density loading of the surface area of
the wire (40 to 60 watts per square inch). A
heavier than normal guage wire is used, giving a
longer coil to maintain required resistance for a
given
wattage.
This
results
in
lower
coil
operating
temperature
which
eliminates
glow
under standard operating conditions because of
the greatly increased surface area and also gives a
sturdier element for longer life.
F - MODULAR FRAME AND CHANNEL
RACK
The HF series heaters are furnished with a new
galvanized,
(aluminized
optional)
modular
frame. This design has made it possible for easier
servicing in the field should this be necessary.
The new HF channel rack has been designed to
give added rigidity and also improved heat
dissipation due to staggering of the rows of
heating elements. (See Below)
FIGURE 13 - Element Termination
H - INSULATING BUSHINGS
The high temperature special ceramic bushings,
which insulate the coils from supporting metal,
float freely in specially designed element racks.
The floating ceramics will not crack or bind due
to heating and cooling of the element.
I - STEEL WELDED SAFETY SCREEN
When the requirements for additional safety
from possible contact to the heating elements of
a duct heater, either from entering air or leaving
air side, a screening material is available factory
installed and UL approved as an option. Refer to
Optional Pricing Section.
J - ELECTRIC DUCT HEATERS FOR
MULTI-ZONE APPLICATIONS
For many years Inducto has been developing
and
manufacturing
heaters
for
multi-zone
applications. This type of application has been
used in office buildings, auditoriums, schools,
and many other constructions where different
conditioning is required at one time.
The air flows in this type of unit are controlled
FIGURE 12 - Typical Channel Rack
6
Page 6 -CONSTRUCTION
6 - CAPILLARY TYPE AUTOMATIC AND
MANUAL RESETS
Each heater contains double protection in the
use of the capillary type automatic and manual
reset limits. Both types of safety devices have
capillaries extending the full length of the. heater
and can sense thermal overload at any point
along its length. Upon sensing the over
temperature the unit is shut down.
by hot deck and cold deck dampers, each having
a possible air flow from zero to 100 percent.
Therefore a zone calling for 100 percent heat
would have its cold damper closed and the hot
damper fully open. The opposite is true when
100 percent cold air is required. Two adjacent
zones, serving separate sections of a building,
could have the dampers in an opposite position
mode. This results in a variable air flow pattern
across the heating coil.
Therefore, special considerations must be made
when designing an electric heater for the'
multi-zone application.
These special design characteristics are as
follows:
7 - DISTANCE TO DAMPERS
The distance between zone dampers and the coil
should be at least 18 inches. If this distance is
not maintained, overheating of the coil may
result.
8 - CONTROLLING MEANS
The stages of the heating coil should be
controlled by a temperature sensing device
placed in the leaving air stream. The steps of the
heater should be decreased as the rise
requirements are decreased. This decreases the
density of the coil as less temperature rise is
required and air flow decreased.
All of the Inducto multi-zone heaters are
constructed with open coil elements because of
their better operating characteristics over the
finned tubular elements. These advantages are
discussed on page 10 section II Construction paragraph E.
The combination of Inducto multi-zone heaters
and multi-zone units should be made in
accordance with NEC and local governing codes.
The Inducto multi-zone heaters will be built in
accordance with
Underwriters Laboratories
Standards; however, they will not bear the UL
label due to the vast testing required of the
many different combinations.
1 - LOW DENSITY ELEMENTS
Low watt density coils are required to reduce
surface temperatures to a minimum during low
air flow operation. The Inducto elements are
derated to one-half or less than the normal watt
density. This prolongs element life and decreases
radiation.
2 - MINIMUM NUMBER OF STEPS
Due to the various amounts of KW required and
space available in the hot decks, each application
must be considered separately as to the number
of steps. In any case, less than three steps are
not recommended. The greater the number of
steps, the greater the uniformity of temperature
control.
3- FREE AREA
Each multi-zone unit must have the electric
heater specifically designed for its free area of
air flow. All restrictions as to air flow must be
considered in order to assure that all regulating
and safety controls are in the air stream as well
as the entire face of the heater. This assures that
safety limits are able to function properly giving
maximum protection and eliminating undue
cycling which would decrease element life.
4 - ELIMINATION OF STRATIFICATION
In order to prevent stratification and use the
maximum amount of air flowing across the coil,
each step should have a spread across the full
face of the heater. This is necessary especially
when only one or two dampers are open.
5-BAFFLE PLATES
Perforated baffle plates should be provided on
the air inlet side of the heater to assure an even
air distribution across the face of the coil. This is
an important function in low air flow usage of
the coil.
7
INSTALLATION DESIGN AND PROCEDURES - Page 7
A-GENERAL DESIGN INFORMATION
TEMPERATURE RISE
The air temperature rise through the heater is 9
factor of great importance. The chart should be
consulted for the temperature rise expected to
result from the air flow and watt density used.
1 - The Temperature Rise Chart (Fig. 1) aids
in calculating requirements or results from the
known factors of FPM, CFM, Temperature Rise,
Total KW, or KW per square foot. If two related
factors are known, the others can be
determined.
EXAMPLE B
VELOCITY (FPM)-WATT DENSITY (KW PER
SQ. FT.) To find the watt density (KW per sq.
ft.) at a given temperature rise and F.P.M. of air,
use bottom and left scales.
EXAMPLE: To find the heat input in a duct
handling 700 F.P.M. of air, with a temperature
rise of 60ºF.
1. Draw a line vertically up from the 700
F.P.M. on the bottom scale to the 60°F.
temperature rise line.
2. From the point of intersection draw a
horizontal line to the left side scale giving
13.5 KW per sq. ft. of duct area.
2 - Minimum Velocity Requirements: Electric
duct heaters are different from steam or hot
water coils, in that the B.T.U. output remains
constant as long as the heater is energized. To
eliminate over-heating and burn out due to low
air velocity, an automatic re-set temperature
limiting control is built into each heater. The
minimum velocity required to prevent nuisance
tripping of the temperature limiting control is
determined from the air velocity chart (Fig.
2 on the basis of entering air temperature, and
watts per square foot of cross sectional duct
area.
CFM
CAUTION - DO NOT OPERATE WITHOUT
PROPER AIR FLOW
For efficient and trouble free operation it is
important that air flow be adequate over the
complete heating area and particularly at
element terminals. No electric duct heater
should ever be operated with insufficient air
flow because overheating and subsequent
malfunction may result. The minimum air
velocity required at any point should be
determined from the graph following.
MINIMUM AIR VELOCITY
REQUIRED FOR PROPER OPERATION
FIGURE 1
NOTES:
(A) For values above or below those on the scale, multiply or
divide the known factors by a convenient number. Make the
necessary calculations on the chart, then multiply or divide the
answer by the original number for the actual value.
(B) If any two factors are known the third may be calculated in
a similar manner.
EXAMPLE A
Air (CFM)-(KW) Total Heat Required
To find the total heat required at a given
temperature rise and CFM, use the top and right
scales.
EXAMPLE: The heat required to achieve a 40°F
temperature rise in a duct handling 12,000
C.F.M.
1. Draw a line vertically down from the
12,000 C.F.M. on the top scale to the
40°F. temperature rise line.
2. From the point of intersection draw a
horizontal line to the right side scale.
Giving total heat required 150 KW.
Formula: H X W divided by 144 = sq. ft. /area
KW divided by area = KW/sq. ft. duct area (density)
H = Element Frame Height
W = Element Frame Width
8
Page 8 - INSTALLATION DESIGN AND PROCEDURES
3 - Available Watt Density: "HF" series Inducto
Duct Heaters are built to the wattage and
dimensions as specified by the customer.
The "HF" series heaters are available to 1000
KW in all wattages up to 20 KW per square foot
of cross sectional duct area and are suitable for
installation with zero clearance to combustible
surfaces and up to 100 degrees Fahrenheit inlet
temperature. These heaters are available through
20 feet in width.
C - INSTALLATION RESTRICTIONS
The following are stated requirements of UL
regarding installation of duct heaters.
B - INSTALLATION RECOMMENDATIONS
1 - Should be installed at least 4 feet from a heat
pump or central air conditioning unit.
FIGURE 3
FIGURE 7
2 - No clearance is required between the duct
and combustible surfaces around the duct for
Inducto "HF" series duct heaters.
FIGURE 4
1 -The heater must be installed to assure equal air
flow through the entire face area of the heater.
Refer to N EC par. 424-59.
FIGURE 8
3 - A duct heater must not be installed so that the
heating
element
coils
are
strung
vertically
through the supporting racks.
FIGURE 5
2 - A canvas vibration insulation connector should
not be located less than 18 inches from a duct
heater. If it is located closer, an asbestos
connector should be used.
DUCT HEATER PRESSURE DROP
9
INSTALLATION DESIGN AND PROCEDURES • Page 9
Series HF
INSTALLATION. OPERATING AND MAINTENANCE
INSTRUCTIONS
FOR INDUCTO ELECTRIC DUCT HEATERS
APPLICATION REQUIREMENTS
1. The duct system must provide uniform air flow
over the entire face area of the heating
elements.
2. For satisfactory and safe operation the
minimum air velocity must be maintained as
determined from table.
3. The air duct should be installed in accordance
with the standards of the National Fire
Protection Association for the installation of
air-conditioning and ventilating systems of
other than residence-type (Pamphlet No. 90A)
and residence-type warm air heating and
air-conditioning systems (Pamphlet No. 90B).
4. The heater should be installed at least 48 in.
from the duct flanges of a heat pump or central
air conditioner.
3. Insert Type (Fig. 1) - Cut a hole in the side of
the duct 1/8" larger than the element housing
(H-1 x C) and insert the heater. Attach the back
of the terminal box to the duct.
4. Flanged Type (Fig. 2) - Provide duct flanges to
match heater flanges. Attach the heater to the
duct flanges with screws.
5. Maximum inlet air temperature is 100° F.
6. Series HF heaters may be installed in duct
systems having zero clearance to combustible
surfaces.
INSTALLATION PROCEDURES
1. Make sure air flow arrow on heater corresponds
to air flow through the duct and heater is
properly positioned if marked with "top."
2. The heater terminal compartment should not be
enclosed by insulation, etc.
HF 9-2-7 5
10
Page 10 - INSTALLATION DESIGN AND PROCEDURES
ELECTRICAL WIRING INSTRUCTIONS
SIZING OF SUPPLY CONDUCTORS
WARNING:
DISCONNECT
ALL
POWER
SOURCES
BEFORE DOING ANY WORK ON THE HEATER
INSTALLATION.
1. Use the wiring diagram supplied with the heater as a
guide in correlating field wiring with the heater internal
wiring. If there is more than one heating step, wire the
unit so the steps are energized in the same sequence as
numbered in the heater.
2. All field wiring to the heater must meet the
requirements of the N.E.C. and applicable local codes.
3. Wiring to the heater must be rated for 75° C. minimum.
4. Supply conductors must be sized to carry at least 125%
of the ampere load of the circuit it supplies.
5. For low voltage control circuits, use NEC Class 1 wiring
as described in Article 725 of the National Electrical
Code.
6. The fan must be interlocked with the heater so that the
heater is not energized unless the fan is on. A typical
method of accomplishing this is shown on the wiring
diagram, if it is not built in.
7. If contactors are field supplied, they must have adequate
ratings for the load carried and be UL listed for 100,000
cycles of operation. Do not exceed the control circuit
volt-ampere rating marked at the control terminal block.
8. If heater does not have a built-in disconnect switch or
main circuit breaker, install a remote disconnect (furnished by others) in accordance with the National Electrical Code, Article 424-65.
9. Do not bundle, tie or wrap power wiring in groups as
this may cause over-heating and eventual breakdown of
insulation.
10. For low voltage control circuits using two supply
transformers with a heating-cooling thermostat, one for
heating and one for cooling, a thermostat with isolating
contacts must be used to prevent interconnection of the
two different circuits.
Caution: For successful service using aluminum wiring,
special treatment of all connections is an absolute necessity
in order to prevent high resistance and oxidation problems.
For recommended practice check with your local electrical
utility.
OVERCURRENT PROTECTION
UL requires compliance with paragraph 424-22 (b) of the National Electrical Code as follows: "Electric space heating
equipment employing resistance type heating elements
rated more than 48 amperes shall have the heating elements
subdivided. Each subdivided load shall not exceed 48
amperes and shall be protected at not more than 60
amperes."
This means that sub-circuit overcurrent protection must be
provided if the total heater load exceeds 48 amperes. If overcurrent protection is not built-in, all heaters exceeding 48
amperes total line current are divided into a sufficient
number of sub-circuits, each provided with line terminals for
connection to remote overcurrent protection.
The required minimum size of supply conductors is marked
at the field wiring terminals within the heater control box,
however for reference the following table is included. The
wire gauges are calculated for 125% of the heater line
current as required by the National Electrical Code, Article
424-3 (b) based on conductor insulation rated for 75° C
(167° F)
(1) For 7-24 conductors in a raceway or cable reduce
allowable heater line currents to 87 ½ % of those shown
above.
(2) Based on 30° C (86 °F) ambient temperature. For higher
ambient temperature, see N.E.C. table 310-16 and
310-18 Note 13.
(3) Based on 80% of ratings in table 310-16 N.E.C. for 75 °C
insulation.
(4) Based on 80% of ratings in table 310-18 N.E.C. for 75 °C
insulation.
CALCULATION OF LINE CURRENTS (AMPS)
MAXIMUM KW PER CIRCUIT FOR OVER-CURRENT
To determine the line current, use the following formulae:
Two or more circuits may be paralleled to make one heating
stage.
11
ELECTRICAL DESIGN - Page 11
3 - Ohm's Law
A - GENERAL
The requirements and practices described below
are based on the National Electrical Code and the
Space Heating Standard of the Underwriters
Laboratories, Inc. (UL). Although UL requirements
are uniform throughout the country, local electrical
codes may deviate from the National Electrical
Code, therefore local inspection authorities should
be consulted regarding local requirements.
After final assembly and before shipping each Inducto duct heater must pass a 2000 volt minimum
dielectric test.
1 - Effect of low voltage on wattage and
B.T.U.: The heating elements may be used on
voltages lower than the design voltage of the
heater, however, the wattage and B.T.U. output
will he reduced to the percentage listed in table 1.
FIGURE 1
DE-RATED WATTAGE FOR LOW VOLTAGE
Heater
Line
% of Heater
Voltage
Voltage
Wattage & B.T.U.
480
277
240
208
120
460
440
265
254
92%
84%,
92%
84%
230
220
208
200
200
190
92%
84%
75%
69%
92%
83%
115
110
92%
84%
Ohm's Law Equation Wheel
This "wheel" shows the equation for calculating
any one of the basic factors of electricity - Watts
(W). Amperes (I), Volts (E) or Ohms (R) - when
any two of these factors are known. The
elements to be calculated are shown on the rim
of the wheel. Each quadrant shows three
equations for solving the unknown; select the
equation appropriate for the known values.
Example: a 2400 Watt Single Phase heater is
connected to a 240 Volt circuit. How many
Amps does it draw?
Solution: Since we are finding Amps, the
formula will be found in the I (Amperes)
section of the wheel.
TABLE 1
W/E = 2400 W ÷ 240 V = 10 Amps
2 - Standard Voltages: Inducto duct heaters are
built in five standard voltage ratings to cover the
voltage ranges listed in Table 2. If a specific
voltage is required, the order must be marked
"specific voltage - V." For heater output on
reduced voltage see Table 1.
What is the Resistance?
2
E /W = R 240 V x 240 V ÷ 2400 W = 24 Ohms
STANDARD VOLTAGES
If you order:
110 V
208V
220V
254V
440V
Ratings
You will get:
115V., etc.
120
V.
208
V.
230V, 236V,
etc.
240
V.
265V, 277V.
277
V.
460V, etc.
480
V.
from 500 V. up to 600V. will be furnished
as
ordered.
TABLE 2
12
Page 12- ELECTRICAL DESIGN
4 - ELECTRICAL CODES AND REGULATIONS The design and installation of electric duct heaters must conform to all codes and regulations apply ing
at the job site in addition to meeting the specifications. These include standards and requirements
published by Underwriters' Laboratories. Inc. (UL), National Electrical Code (NEC). and other
state and local agencies.
Ductwork must be installed in accordance with one of the following standards of the National Fire
Protection Association: Installation of Air Conditioning and Ventilating Systems (1972 Pamphlet
90A), or Residence Type Warm Air Heating and Air Conditioning Systems (1968Pamphlet 90B).
NATIONAL ELECTRICAL CODE
INDUCTO QUALIFICATIONS
Inducto
duct
heaters are designed to comply with
Paragraph 424-58. Approved. Heaters installed
the
provisions
of the National Electrical Code, UL,
in an air duct shall be identified as suitable for the
and other regulations.
installation.
Compliance with this requirement is the
Paragraph 424-59. Air Flow. Means shall be
responsibility of the system designer and
provided to assure uniform and adequate air
installer. Minimum air velocities for Inducto
flow over the face of the heater.
heaters are shown in the installation instructions.
Heaters installed within 4 feet of a fan outlet,
elbows, baffle plates, or other obstruction in
duct work may require turning vanes, pressure
plates, or other devices on the inlet side of the
duct heater to assure an even distribution of air
over the face of the heater.
Inducto heaters are approved for use with heat
Paragraph 424-60. Elevated Inlet Temperature.
pumps. Critical performance data for each
Duct heaters intended for use with elevated inlet
heater is clearly indicated on the heater as well
air temperature (such as heat pumps) shall be
as in the installation instructions. Lower watt
approved for the purpose and so marked.
density heaters may be specified for special
applications.
Paragraph 424-61. Installation of Duct Heaters
with Heat Pumps and Air Conditioners. Heat
pumps and air conditioners having duct heaters
closer than 4 feet to the heat pump or air
conditioner shall have both the duct heater and
heat pump or air conditioner approved for such
installation and so marked.
Paragraph 424-62. Condensation. Duct heaters
used with air conditioners or other air-cooling
equipment that may result in condensation of
moisture shall be approved for use with air
conditioners.
This pertains to the design and installation of
heat pumps rather than to duct heaters. Inducto
does recommend that a duct heater should be
installed at least 4 feet downstream from heat
pumps and air conditioners and at least 2 feet
downstream from air handlers.
All Inducto duct heaters are assembled with a
1/2" fiberglass board insulation permanently
attached to the duct side of the control
compartment as standard. This construction
provides
maximum
protection
against
condensation. These heaters are UL listed and
marked - "For use with heat pumps or central
air conditioners."
Inducto heaters are available on order with a
built-in airflow switch, or fan interlock relay.
Paragraph 424-63. Fan Circuit Interlock. Means
shall be provided to insure that the fan circuit is
energized when the first heater circuit is
energized.
However, time or temperature
controlled delay in energizing the fan motor
shall be permitted.
SPECIFICATIONS SUBJECT TO CHANGE WITHOUR NOTICE
13
All Inducto standard and custom duct heaters include
a primary auto-reset high limit switch and a secondary
disc type replaceable - all readily accessible in the
heater control compartment.
Paragraph 424-64. Limit Controls. Each duct
heater shall be provided with an approved,
integral,
automatic-reset
temperature-limiting
control or controllers to de-energize the circuit
or circuits.
In
addition,
an
integral
independent
supplementary control or controllers shall be
provided in each duct heater that will
disconnect a sufficient number of conductors to
interrupt current flow. This device shall be
manually resettable or replaceable.
Paragraph 424-65. Location of Disconnecting
Means. Duct heater controller equipment shall
be accessible with the disconnecting means
installed at or within sight from the controller.
Paragraph 424-20. Controllers and
Disconnecting Means.
(a) Thermostats and thermostatically
controlled switching devices that indicate an off
position and interrupt line current shall open all
ungrounded conductors when the control device
is in this off position.
(b) Thermostats and thermostatically
controlled switching devices that do not have an
off position shall not be required to open all
ungrounded conductors.
(c) Remote-control thermostats shall not be
required to meet the requirements of (a) and (b)
above. These devices shall not be considered as
the disconnecting means.
(d) Switching devices consisting of combined
thermostats and manually controlled switches
that serve both as controllers and disconnecting
means shall:
(1) Open all ungrounded conductors when
manually placed in the off position.
(2) Be so designed that the circuit cannot
be energized automatically after the device has
been manually placed in the off position.
Paragraph 424-22. Overcurrent Protection.
(b) Resistance Elements.
Electric space
heating equipment employing resistance-type
heating elements rated more than 48 amperes
shall have the heating elements subdivided. Each
subdivided load shall not exceed 48 amperes and
shall be protected at not more than 60 amperes.
(c) Overcurrent Protective Devices. The
overcurrent protective devices specified in (b)
above shall be: (1) factory-installed within or on
the heater enclosure or provided as a separate
assembly by the heater manufacturer; (2)
accessible, but shall not be required to be readily
accessible; and (3) suitable for branch-circuit
protection.
Inducto custom heaters may be ordered with a
factory installed electrical disconnect switch
sized to the total heater capacity (200 amp max.
per switch).
Inducto heaters are furnished with built-in
contactors and other control devices for total
disconnect of all ungrounded conductors or for
circuit de-energizing. Circuit de-energizing will
normally be furnished.
To meet this requirement, Inducto heaters are
available with
built-in fusing and circuit
breakers. All heaters exceeding 48 amperes total
line current are divided into subcircuits (as
allowed by stages) of less than 48 amperes and
are protected at not more than 60 amperes. The
main conductors supplying these overcurrent
protective devices are considered branch circuit
conductors and are subject to the 125% ampere
rating rule.
14
4 - Electrical Codes and Regulations (Cont.)
Underwriters Laboratories Inc. Standards for Safety No. 1096
UL REQUIREMENTS
TRANSFORMER PRIMARY
OVERCURRENT PROTECTION
17.11 Overcurrent protection at not more than
20 amperes shall be provided by a suitable
circuit breaker or fuses, as a part of the heater,
(1) for each general-use duplex receptacle
circuit, (2) for each transformer primary circuit,
except as indicated in paragraph 17.14, and (3)
for each lampholder circuit, except as indicated
in paragraph 17.12, independent of a heating
element, unless the heater would be properly
connected in accordance with the National
Electrical Code to a branch circuit rated at 20
amperes or less. See para graph 35.2.
17.14 The overcurrent protection may be
omitted from the primary of a Class 2
transformer.
35.2 A heater intended for use of a 15 or 20
ampere circuit, as indicated in paragraph 7.12,
shall be marked; Use Only On
a
Ampere
Branch Circuit.
INDUCTO QUALIFICATIONS
Inducto Heaters
are
provided
with
a
control transformer when specified or requested.
When a control transformer is built-in to a
heater or remote control panel the primary of
the transformer will be protected per code and
the standard requirement is: (a) Class II trans.
are integrally protected and will be additionally
protected only when specifically requested, (b)
All other transformers will be connected within
the heater to a circuit of 16 amp. maximum if
available, otherwise separate primary fusing will
be installed. Though not required the secondary
of the transformer will be fused if specified.
a
The number 15 or 20 as appropriate.
FACTORY INSTALLED CONTROLS
23.12 A contactor or similar device, such as a
silicon controlled rectifier, required for use with
a limit control shall be provided by the
manufacturer of the heater, but need not be
mounted on the heater. See paragraph 34.10.
34.10 If required overcurrent protective devices
or contactors are provided as a separate
assembly, see paragraphs 17.2 and 23.12, the
heater shall be marked to indicate that it is to be
used only with this separate assembly.
17.2 The overcurrent protective devices required
by paragraph 17.1 shall be provided as an
integral part of the heater or shall be provided
by the heater manufacturer as a separate
assembly, for independent mounting, for use
with the heater. See paragraph 34.10.
In some applications the required components
cannot be built in the duct heater terminal box
because of space limitations, inaccessibility, etc.
In this case some, or all, of the components can
be mounted and factory wired internally, as
applicable, in a panel for remote mounting. All
terminals are marked to clearly indicate the field
connections between the panel and the heater.
The panel is of the same construction as the
heater terminal box and the same components
will be used as previously described in this
catalogue for use in the Inducto duct heater.
Both the heater and the remote control panel
must be UL listed, so labeled, and completely
coordinated.
SPECIFICATIONS SUBJECT TO CHANGE Wl TH OUT NOTICE
15
ELECTRICAL DESIGN . Page 15
CONTROL COMPARTMENT COVER
5.11 Except as indicated in paragraph 5.13, the
door or cover of an enclosure shall be hinged (1)
if it gives access to any fuse, circuit breaker, or
manually resettable temperature control in other
than a low-voltage circuit, and (2) if uninsulated
live parts are exposed during the normal
replacement of the fuse or resetting of the
manually resettable device. Such a door or cover
shall also be provided with an automatic latch,
see paragraph 5.15, or the equivalent and, if live
parts other than the screw shell of a plug
fuseholder are exposed inside the enclosure, a
captive screw or equivalent means, requiring the
use of a tool to open, to reliably secure the door
or cover in place. See paragraph 5.12.
5.15 A spring latch, a magnetic latch, a dimple,
or any other mechanical arrangement that will
hold the door closed, and would require some
effort on the user's part to open it, is considered
to be a suitable means for holding the door
closed as required in paragraph 5.11.
5.12 The captive screw may be omitted from
the door or cover over the compartment housing
the uninsulated live parts if it is provided in the
cover that must be opened to gain access to the
door or cover. Arrangements employing two
mating hinged doors are acceptable where the
automatic latch and captive screw are provided
only on one door (1) if that door is designed to
be opened first and closed last, and (2) if the
latch and screw will hold the other door closed.
ZERO CLEARANCE
44.2 If spacings between combustible material
and the duct in which a duct heater is installed
must be no less than a specified distance to
prevent attainment of hazardous temperatures
on that material, the heater shall bear a suitable
warning marking to convey this information. See
paragraph 36.6.
36.6 A duct heater rated 50 kilowatts (kw) or
less shall be suitable for installation with zero
spacing between the duct and combustible
surfaces. A duct heater rated more than 50 kw
may necessitate that such spacings be larger than
zero.
All Inducto duct heater control compartments.
whether integral or remote, are provided with a
piano type hinge on the longest cover dimension
or on any side specified.
All covers are provided with an approved latch
requiring a tool to open and a pull ring to
facilitate opening the cover.
All covers over 48" long are provided with two
latches and pull rings.
Inducto Heaters Series "HF" are UL listed for
zero clearance up to 1000 KW.
16
B - HEATER POWER CIRCUITRY
See wiring diagrams for details of the various
wiring systems mentioned below.
All stages of a heater are of equal KW unless
specified otherwise. For pricing of unequal
stages, see Pricing Section.
5 - Power Wire Sizing:
If a long run of wire is required or more than
three wires are run in a conduit the allowable
capacity on a given wire size must be reduced as
per NEC requirements (see note 13 to NEC
Table 310-16 and 310-18)
MAXIMUM AMP LOAD ALLOWED ON VARIOUS
WIRE SIZES FOR. FIELD WIRING TO DUCT HEATERS
De-Rated 20%
1 - Single phase power circuits: Each circuit
consists of a heating coil (or coils connected
parallel) which cannot exceed 48 amp for
over-current protection.
A single stage heater may be controlled directly
by a line voltage thermostat without using a
controlling contactor if the heater rating is
within the rating of the thermostat, the
over-temperature protection controls and the
fan interlock.
Larger loads are controlled by contactors, S.C.R.
controllers or load carrying step controllers.
2 - Balanced Three Phase Power Circuits: Each
circuit cannot exceed 48 amp for over-current
protection and consists of three (or a multiple of
three) heating coils factory connected in delta or
wye system at the factory's option. The load
will be balanced (equal) among the three phases
and the entire circuit is controlled as a unit and
operates identically whether the power source is
three or four wire. Therefore a neutral terminal
is not furnished on balanced circuits.
Each circuit is normally controlled by a
contactor which in turn is controlled by a
thermostat or step controller in the control
circuit.
TABLE 3
TABLE 4
Except From Table 3A - NEC Maximum Number of Conductors in Trade Sizes of Conduit or Tubing
(Based on Table 1, Chapter 9)
17
TABLE 5
TOTAL AMPERAGE RATING CHART
K.W.
Rating
B.T.U.H.
208
AMP
Volts
Rating
220
AMP
Volts
Rating
230
AMP
Volts
Rating
240 Volts
AMP Rating
0.5
1.0
2.0
1,706
3,413
6.826
3.0
4.0
5.0
6.0
440
Volts
AMP
Rating
480
Volts
AMP
Rating
550
Volts
AMP
Rating
1 PH
3 PH
1 PH
3 PH
1 PH
3 PH
1 PH
3 PH
02.4
04.8
09.6
01.4
02.8
05.6
02.3
04.5
09.1
01.3
02.6
05.2
02.2
04.3
08.7
01.3
02.5
05.0
02.1
04.2
08.3
01.2
02.4
04.8
1 PH
3 PH
3 PH
3 PH
01.8
03.6
07.2
0.7
1.3
2.6
0.6
1.2
2.4
0.5
1.0
2.1
10,239
14.4
08.3
13.6
07.9
13.0
07.5
12.5
13,652
17,065
20,478
19.2
24.0
28.8
11.1
13.9
16.7
18.2
22.7
27.3
10.5
13.1
15.7
17.4
21.7
26.1
10.0
12.6
15.1
16.7
20.8
25.0
07.2
10.8
3.9
3.6
3.1
09.6
12.0
14.4
14.4
18.1
21.7
5.2
6.6
7.9
4.8
6.0
7.2
4.2
5.2
6.3
7.0
8.0
23,891
27,304
33.7
38.5
19.4
22.2
31.8
36.4
18.4
21.0
30.4
34.8
17.6
20.1
29.2
33.3
16.8
19.2
25.3
28.9
9.2
10.5
8.4
9.6
7.3
8.4
9.0
30,717
43.3
25.0
40.9
23.6
39.1
10.0
34,130
48.1
27.8
45.5
26.2
43.5
22.6
37.5
21.7
32.5
11.8
10.8
9.4
25.1
41.7
24.1
36.1
13.1
12.0
11.0
37,543
52.9
30.5
50.0
28.9
10.5
47.8
27.6
45.8
26.5
39.7
14.4
13.2
12.0
13.0
40,956
44,369
57.7
62.5
33.3
36.1
54.5
59.1
11.5
31.5
34.1
52.2
56.5
30.1
32.6
50.0
54.2
28.9
31.3
43.3
46.9
15.7
17.1
14.4
15.6
12.6
13.6
14.0
15.0
16.0
17.0
47.782
51,195
54,608
58,021
67.3
72.1
76.9
81.7
38.9
41.6
44.4
47.2
63.6
68.2
72.7
77.3
36.7
39.4
42.0
44.6
60.9
65.2
69.6
73.9
35.1
37.7
40.2
42.7
58.3
62.5
66.7
70.8
33.7
36.1
38.5
40.9
50.5
54.2
57.8
61.4
18.4
19.7
21.0
22.3
16.8
18.0
19.2
20.4
14.7
15.7
16.8
17.8
18.0
19.0
61,434
64,847
86.5
91.3
50.0
52.7
81.8
86.4
47.2
49.9
78.3
82.6
45.2
47.7
75.0
79.2
43.3
45.7
65.0
68.6
23.6
24.9
21.7
22.9
18.9
19.9
20.0
21.0
68,260
71,673
96.2
101.0
55.5
58.3
90.9
95.5
52.5
55.1
87.0
91.3
50.2
52.7
83.3
87.5
48.1
50.5
72.2
75.8
26.2
27.6
24.1
25.3
21.0
22.0
22.0
23.0
24.0
75,086
105.8
61.1
100.0
57.7
95.7
55.2
91.7
52.9
79.4
28.9
26.5
23.1
78,499
81.912
110.6
115.4
63.8
66.6
104.5
109.1
60.4
63.0
100.0
104.3
57.7
60.2
95.8
100.0
55.3
57.7
83.0
86.6
30.2
31.5
27.7
28.9
24.1
25.2
25.0
26.0
27.0
85,325
88,738
92.151
120.2
125.0
129.8
69.4
72.2
74.9
113.6
118.2
122.7
65.6
68.2
70.9
108.7
113.0
117.4
62.8
65.3
67.8
104.2
108.3
112.5
60.1
62.5
65.0
90.3
93.9
97.5
32.8
34.1
35.4
30.1
31.3
32.5
26.2
27.3
28.3
28.0
29.0
95,564
98,977
134.6
139.4
77.7
80.5
127.3
131.8
73.5
76.1
121.7
126.1
70.3
72.8
116.7
120.8
67.4
69.8
101.1
104.7
36.7
38.1
33.7
34.9
29.4
30.4
30.0
102,390
144.2
83.3
136.4
78.7
130.4
75.3
125.0
72.2
108.3
39.4
36.1
31.5
31.0
105,803
149.0
86.0
140.9
81.4
134.8
77.8
129.2
74.6
111.9
40.7
37.3
32.5
32.0
33.0
109,216
112.629
153.8
158.7
88.8
91.6
145.5
150.0
84.0
86.6
139.1
143.5
80.3
82.8
133.3
137.5
77.0
79.4
115.5
119.1
42.0
43.3
38.5
39.7
33.6
34.6
34.0
35.0
116,042
119,455
163.5
168,3
94.4
97.2
154.5
159.1
89.2
91.9
147.8
152.2
85.3
87.9
141.7
145.8
81.8
84.2
122.7
126.4
44.6
45.9
40.9
42.1
35.7
36.7
36.0
122,868
173.1
99.9
163.6
94.5
156.5
90.4
150.0
86.6
130.0
47.2
43.3
37.8
37.0
126,281
177.9
102.7
168.2
97.1
160.9
92.9
154.2
89.0
133.6
48.6
44.5
38.8
38.0
129.694
182.7
105.5
172.7
99.7
165.2
95.4
158.3
91.4
137.2
49.9
45.7
39.9
39.0
133,107
187.5
108.3
177.3
102.4
169.6
97.9
162.5
93.8
140.8
51.2
46.9
40.9
40.0
41.0
136,520
139.933
192.3
197.1
111.0
113.8
181.8
186.4
105.0
107.6
173.9
178.3
100.4
102.9
166.7
170.8
96.2
98.6
144.4
148.0
52.5
53.8
48.1
49.3
42.0
43.0
42.0
43.0
44.0
143.346
146,759
150,172
201.9
206.7
211.5
116.6
119.4
122.1
190.9
195.5
200.0
110.2
112.8
115.5
182.6
187.0
191.3
105.4
107.9
110.5
175.0
179.2
183.3
101.0
103.4
105.9
151.6
155.2
158.8
55.1
56.4
57.7
50.5
51.7
52.9
44.1
45.1
46.2
45.0
46.0
153,585
156.998
216.3
221.2
124.9
127.7
204.5
209.1
118.1
120.7
195.7
200.0
113.0
115.5
187.5
191.7
108.3
110.7
162.5
166.1
59.0
60.4
54.1
55.3
47.2
48.3
47.0
160,411
226.0
130.5
213.6
123.3
204.3
118.0
195.8
113.1
169.7
61.7
56.5
49.3
48.0
49.0
50.0
163,824
167,237
170,650
230.8
235.6
240.4
133.2
136.0
138.8
218.2
222.7
227.3
126.0
128.6
131.2
208.7
213.0
217.4
120.5
123.0
125.5
200.0
204.2
208.3
115.5
117.9
120.3
173.3
176.9
180.5
63.0
64.3
65.6
57.7
58.9
60.1
50.4
51.4
52.5
51.0
52.0
174.063
177.476
245.2
250.0
141.6
144.3
231.8
236.4
133.8
136.5
221.7
226.1
128.0
130.5
212.5
216.7
122.7
125.1
184.1
187.7
66.9
68.2
61.3
62.5
53.5
54.6
53.0
54.0
180,889
184.302
254.8
259.6
147.1
149.9
240.9
245.5
139.1
141.7
230.4
234.8
133.0
135.6
220.8
225.0
127.5
129.9
191.3
194.9
69.5
70.9
63.8
65.0
55.6
56.7
55.0
187,715
264.4
152.7
250.0
144.3
239.1
138.1
229.2
132.3
198.6
72.2
66.2
57.7
56.0
191,128
269.2
155.4
254.5
147.0
243.5
140.6
233.3
134.7
202.2
73.5
67.4
58.8
57.0
194,541
274.0
158.2
259.1
149.6
247.8
143.1
237.5
137.1
205.8
74.8
68.6
59.8
58.0
197,954
278.8
161.0
263.6
152.2
252.2
145.6
241.7
139.5
209.4
76.1
69.8
60.9
59.0
201,367
283.7
163.8
268.2
154.8
256.5
148.1
245.8
141.9
213.0
77.4
71.0
61.9
60.0
204,780
288.5
166.5
272.7
157.5
260.9
150.6
250.0
144.3
216.6
78.7
72.2
63.0
18
277
Volts
AMP
Rating
Page 18. ELECTRICAL DESIGN
TOTAL AMPERAGE RATING CHART (CONT'D)
K.W.
Rating
B.T.U.H.
208 Volts
AMP Rating
220 Volts
AMP Rating
230 Volts
AMP Rating
240 Volts
AMP Rating
277
Volts
AMP
Rating
440
Volts
AMP
Rating
480
Volts
AMP
Rating
550
Volts
AMP
Rating
1 PH
3 PH
1 PH
61.0
208,193
293.3
169.3
277.3
3 PH
1 PH
3 PH
1 PH
3 PH
1 PH
3 PH
3 PH
3 PH
160.1
265.2
153.1
254.2
146.7
220.2
80.0
73.4
62.0
211,606
298.1
172.1
64.0
281.8
162.7
269.6
155.6
258.3
149.2
223.8
81.4
74.6
63.0
64.9
65.0
215,019
218,432
221,845
302.9
307.7
312.5
65.1
174.9
177.7
180.4
286.4
290.9
295.5
165.3
168.0
170.6
273.9
278.3
282.6
158.1
160.7
163.2
262.5
266.7
270.8
151.6
154.0
156.4
227.4
231.0
234.7
82.7
84.0
85.3
75.8
77.0
78.2
66.1
67.2
68.2
66.0
225,258
67.0
228,671
317.3
183.2
300.0
173.2
287.0
165.7
275.0
158.8
238.3
86.6
79.4
69.3
322.1
186.0
304.5
175.8
291.3
168.2
279.2
161.2
241.9
87.9
80.6
68.0
69.0
70.3
232,084
235,497
326.9
331.7
188.8
191.5
309.1
313.6
178.5
181.1
295.7
300.0
170.7
173.2
283.3
287.5
163.6
166.0
245.5
249.1
89.2
90.5
81.8
83.0
71.4
72.4
70.0
71.0
72.0
238,910
242,323
245,736
336.5
341.3
346.2
194.3
197.1
199.9
318.2
322.7
327.3
183.7
186.3
189.0
304.3
308.7
313.0
175.7
178.2
180.7
291.7
295.8
300.0
168.4
170.8
173.2
252.7
256.3
259.9
91.9
93.2
94.5
84.2
85.4
86.6
73.5
74.5
73.6
73.0
74.0
249,149
252,562
351.0
355.8
202.6
205.4
331.8
336.4
191.6
194.2
317.4
321.7
183.3
185.8
304.2
308.3
175.6
178.0
263.5
267.1
95.8
97.1
87.8
89.0
76.6
77.7
75.0
255,975
360.6
208.2
340.9
196.8
326.1
188.3
312.5
180.4
270.8
98.4
90.2
78.7
76.0
77.0
259,388
262.801
365.4
370.2
211.0
213.7
345.5
350.0
199.5
202.1
330.4
334.8
190.8
193.3
316.7
320.8
182.8
185.2
274.4
278.0
99.7
101.0
91.4
92.6
79.8
80.8
78.0
79.0
80.0
266,214
269,627
273,040
375.0
379.8
384.6
216.5
219.3
222.1
354.5
359.1
363.6
204.7
207.3
210.0
339.1
343.5
347.8
195.8
198.3
200.8
325.0
329.2
333.3
187.6
190.1
192.5
281.6
285.2
288.8
102.4
103.7
105.0
93.8
95.0
96.2
81.9
82.9
84.0
81.0
276,453
389.4
224.8
368.2
212.6
352.2
203.3
337.5
194.9
292.4
106.3
97.4
85.0
82.0
279,866
394.2
227.6
372.7
215.2
356.5
205.8
341.7
197.3
296.0
107.6
98.6
86.1
83.0
84.0
283,279
286,692
399.0
403.8
230.4
233.2
377.3
381.8
217.8
220.4
360.9
365.2
208.4
210.9
345.8
350.0
199.7
202.1
299.6
303.2
108.9
110.2
99.8
101.0
87.1
88.2
85.0
290,105
408.7
235.9
386.4
223.1
369.6
213.4
354.2
204.5
306.9
111.5
102.2
89.2
86.0
87.0
88.0
293.518
296,931
300,344
413.5
418.3
423.1
238.7
241.5
244.3
390.9
395.5
400.0
225.7
228.3
230.9
373.9
378.3
382.6
215.9
218.4
220.9
358.3
362.5
366.7
206.9
209.3
211.7
310.5
314.1
317.7
112.8
114.2
115.5
103.4
104.6
105.9
90.3
91.3
92.4
89.0
303,757
427.9
247.0
404.5
233.6
387.0
223.4
370.8
214.1
321.3
116.8
107.1
93.4
90.0
307,170
432.7
249.8
409.1
236.2
391.3
225.9
375.0
216.5
324.9
118.1
108.3
94.5
91.0
92.0
310,583
313,996
437.5
442.3
252.6
255.4
413.6
418.2
238.8
241.4
395.6
400.0
228.4
230.9
379.2
383.3
218.9
221.3
328.5
332.1
119.4
120.7
109.5
110.7
95.5
96.6
93.0
94.0
317,409
320,822
447.1
451.9
258.1
260.9
422.7
427.3
244.1
246.7
404.3
408.7
233.5
236.0
387.5
391.7
223.7
226.1
335.7
339.4
122.0
123.3
111.9
113.1
97.6
98.7
95.0
324,235
456.7
263.7
431.8
249.3
413.0
238.5
395.8
228.5
343.0
124.7
114.3
99.7
96.0
327,648
461.5
266.5
436.4
251.9
417.4
241.0
400.0
230.9
346.6
126.0
115.5
100.8
97.0
331,061
466.3
269.3
440.9
254.6
421.7
243.5
404.2
233.4
350.2
127.3
116.7
101.8
98.0
99.0
334,474
337,887
471.2
476.0
445.5
450.0
257.2
259.8
426.1
430.4
246.0
248.5
408.3
412.5
235.8
238.2
353.8
357.4
128.6
129.9
117.9
119.1
102.9
103.9
100.0
105.0
341,300
358,365
480.8
504.8
272.0
274.8
277.6
291.5
454.5
477.3
262.4
275.6
434.8
456.5
251.0
263.6
416.7
437.5
240.6
252.6
361.0
379.1
131.2
137.8
120.3
126.3
105.0
110.2
110.0
375,430
528.8
305.3
500.0
288.7
478.3
276.1
458.3
264.6
397.1
144.3
132.3
115.5
116.0
120.0
392,495
409,560
552.9
576.9
319.2
333.1
522.7
545.5
301.8
314.9
500.0
521.7
288.7
301.2
479.2
500.0
276.7
288.7
415.2
433.2
150.9
157.5
138.3
144.3
120.7
126.0
125.0
130.0
135.0
426.625
443,690
460,755
601.0
625.0
649.0
347.0
360.9
374.7
568.2
590.9
613.6
328.0
341.2
354.3
543.5
565.2
587.0
313.8
326.3
338.9
520.8
541.7
562.5
300.7
312.7
324.8
451.3
469.3
487.4
164.0
170.6
177.1
150.4
156.4
162.4
131.2
136.5
141.7
140.0
477,820
673.1
388.6
636.4
367.4
608.7
351.4
583.3
336.8
505.4
183.7
168.4
147.0
145.0
494,885
697.1
402.5
659.1
380.5
630.4
364.0
604.2
348.8
523.5
190.3
174.4
152.2
150.0
511,950
721.2
416.4
681.8
393.7
652.2
376.5
625.0
360.9
541.5
196.8
180.4
157.5
155.0
160.0
165.0
529,015
546,080
563.145
745.2
769.2
793.3
430.2
444.1
458.0
704.5
727.3
750.0
406.8
419.9
433.0
673.9
695.7
717.4
389.1
401.6
414.2
645.8
666.7
687.5
372.9
384.9
396.9
559.6
577.6
595.7
203.4
210.0
216.5
186.4
192.5
198.5
162.7
168.0
173.2
170.0
580,210
817.3
471.9
772.7
446.1
739.1
426.7
708.3
409.0
613.7
223.1
204.5
178.5
175.0
597,275
841.3
485.8
795.5
459.3
760.9
439.3
729.2
421.0
631.8
229.6
210.5
183.7
180.0
614,340
865.4
499.6
818.2
472.4
782.6
451.9
750.0
433.0
649.8
236.2
216.5
189.0
185.0
190.0
631,405
648,470
889.4
913.5
513.5
527.4
840.9
863.6
485.5
498.6
804.3
826.1
464.4
477.0
770.8
791.7
445.1
457.1
667.9
685.9
242.8
249.3
222.5
228.5
194.2
199.5
195.0
665,535
937.5
541.3
886.4
511.8
847.8
489.5
812.5
469.1
704.0
255.9
234.6
204.7
200.0
682,600
961.5
555.2
909.1
524.9
869.6
502.1
833.3
481.1
722.0
262.4
240.6
210.0
19
As standard practice balanced three phase
circuits will be furnished for three phase power
unless single phase circuits from three phase
power are specified.
2 - Overcurrent Protection: The NEC par. 424-22
states:
(b) Resistance Elements. Electric space
heating equipment employing resistance-type
heating elements rated more than 48 amperes
shall have the heating elements subdivided. Each
subdivided load shall not exceed 48 amperes and
shall be protected at not more than 60 amperes.
(c)
Overcurrent, Protective Devices. The
overcurrent protective devices specified in (b)
above shall be: (1) factory-installed within or on
the heater enclosure or provided as a separate
assembly by the heater manufacturer; (2)
accessible, but shall not be required to be readily
accessible; and (3) suitable for branch-circuit
protection.
Where cartridge fuses are used to provide this
overcurrent protection, a single, disconnecting
means shall be permitted to be used for the
several subdivided loads.
Fuses and circuit breakers are available with the
heaters, to meet the above requirements, either
built in the terminal box or built in a panel for
remote mounting (see "D - Remote Control
Panels").
The overcurrent protection (fusing or circuit
breakers) must be sized at least 125% of the
circuit load it protects. For example, 60 amp
fuses are required for a 48 amp load. The
maximum KW allowed per various voltages is
shown in table 6.
For heaters drawing 48 amp or less total load,
the branch circuit fusing at the distribution
panel usually meets the NEC requirements,
however, supplementary fusing for each stage
within the heater can be furnished if specified.
As standard practice, small stages will be
grouped to a maximum of 48 amp and fused as
one circuit. This conserves space and is more
economical while meeting all NEC requirements,
however, each stage will be protected separately
when specified.
Dual element fuses are available when specified.
See Pricing Section.
3 - SINGLE PHASE CIRCUITS FROM THREE
PHASE POWER SUPPLY
If the power supply to the heater is three phase
and the heater circuits are to be controlled by:
load carrying switches of a step controller, single
phase S.C.R. controllers, or similar load carrying
device, single phase circuits from three phase
power must be specified. Whether the power
supply is three or four wire system must also be
/
specified.
For three wire systems each circuit is connected
between alternate pairs of phases using the delta
configuration. When any multiple of three
circuits are heating, the load will be balanced.
For four wire systems each single phase circuit is
connected between one phase and the neutral
using alternate phases for consecutive circuits.
NOTE: Some SCR controllers or load carrying
step controllers cannot accept the automatic
over-temperature limits in a control circuit to
de-energize the heater immediately should an
over-temperature condition occur. If this is
the case, magnetic contactors, which are
controlled
by
the
primary,
automatic,
over-temperature
cutouts,
must
also
be
connected in the load circuit to de-energize
the heater preventing over-heating.
C - BUILT-IN COMPONENTS
1 - Internal Heater Wiring: All factory wiring is
UL
labeled.
105°C
thermoplastic
insulated,
copper appliance type wire. As a result of UL
testing the following has been established as the
maximum load per wire size on factory wiring
within the heater (does not apply to field
wiring):
12 AWG 30 Amp maximum
MAXIMUM KW PER CIRCUIT FOR OVERCURRENT
PROTECTION (48 Amp)
Two or more circuits may be paralleled to make one
heating stage.
FIGURE 2 - Typical Fuse block
TABLE 6
20
INSTRUCTIONS
RECOMMENDED PROCEDURE
FOR ALUMINUM TERMINATIONS
GENERAL
To help guard against overheating, the following
procedure is recommended when connecting
aluminum wire.
PROCEDURE
Step 1. Strip the wire of its insulation to the
desired length without ringing or nicking the
wire.
Step 2. Wire brush the stripped portion of
conductor thoroughly.
Step 3. Thoroughly coat stripped conductor
with
oxide inhibiting compound. (Two
recognized compounds are Penetrox A and
Alnox-UG. There may be others available which
will do equally well.)
Step 4. Insert the conductor into the connector
making certain all strands are contained and
tighten the connector screws securely. This
operation should result in the compound oozing
out from between the individual strands of the
conductor. If this does not happen, this is an
indication that an insufficient quantity of
compound was used.
Step 5. Wipe excess compound from area
adjacent to connection because some
compounds contain metallic particles and could
reduce the dielectric strength of the insulating
materials employed.
FIGURE 3 -Typical Circuit Breaker
3 - Power Supply Connections: A heavy duty
terminal block, or blocks, are provided in
Inducto Duct Heaters for each field wiring
connection for both control and power circuits.
The number of power supply circuits required to
a duct heater may depend on the components
that are built in. See built-in fusing and
contactor sections, IV-C-2 and IV-C-4 for an
explanation of our standard practice.
All field connection terminal blocks are designed
to accommodate either copper or aluminum
conductors as required by NEC and UL 1975.
4 - Built-in Magnetic Contactors: For use as
primary
controlling contactors
and for
secondary (backup) contactors (see secondary
protection).
Contactors are built-in only when specified.
One, two, three and four pole are available with
ratings as shown in figures 5, 6, and 7 and
with holding coil voltages of 24, 120, 208/240,
or 277V. The holding coil data, symbol and part
number (where applicable) are also listed with
the figure. All are UL listed as control
components, having successfully passed the
100,000 cycle test under 150% of full rated amp
load. The NEC requires that Duct Heater
Controlling Contactors shall be accessible.
In the definite purpose line the different voltage
coils are easily interchangeable among all the
sizes used.
When controlling contactors are built in without
built-in over-current protection, a power line
FIGURE 4 . Typical Power Terminal Block
Special Feature - When several sub-circuits are
required to be fed from one main power supply
terminal, a bus bar type terminal block is used
to eliminate the problems associated with having
multiple wires under one lug.
SPECIFICATIONS
SUBJECT
TO
CHANGE
WITHOUT
NOTICE
21
terminal block will be provided for each group
of stages (or stage) not exceeding 48 ampere
total, keeping to a minimum the number of field
installed supply circuits required, while allowing
for proper fusing in the field as required by both
UL standards and the NEC. This means that
heaters 48 amp or less will require only one
power supply circuit. However, when specified
that. each stage is to be field wired with a
separate circuit for individual fusing, a terminal
block is provided for each stage for field
connections.
STANDARD USAGE PRACTICE
Our standard practice when contactors are
built in, for controlling and/or backup duty, is
to de-energize the circuit only. That is, to use
contactors that will open only enough power
lines to interrupt the flow of current to that
stage being controlled.
Contactors must be used that will disconnect all
ungrounded conductors of the circuit in some
cases, such as:
(a) local or state requirements,
(b) if the control or thermostat is marked
with "OFF,"
(c) by engineering specification.
If any of these conditions exist, disconnecting
type contactors must be specified when
ordering.
For contactor pricing refer to Pricing Section.
FIGURE 6 - THE SINGLE POLE CONTACTOR is a totally
enclosed unit with a rating of 18 amps resistive and 2 HP
inductive at 250 volts.
Coil Data: 10 VA inrush - 5 VA holding
MERCURY
CONTACTORS:
This
type
of
contactor should be used in applications where
minimum noise is a definite factor or where
rapid cycling control systems are used. These
units are rugged with all moving parts totally
sealed within a tube, eliminating all exposed arc.
All mercury contactors, must be installed in an
upright position, therefore the direction of air
flow through the duct must be specified when
specifying this type of contactor. See Pricing
Control circuit voltages available are 24, 120,
208/240, and 277 volt.
FIGURE 5
DEFINITE PURPOSE CONTACTOR: Available in 25,30,40
and 50 amp resistive rating with heavy duty contacts and
encapsulated coil which resists oil, dirt, moisture and
mechanical
damage.
Holding Coil
Coil Voltage
24V 110V
208/
277V
480V
240V
Contactor
symbol
VA inrush
VA holding
Replacement
part No.
24
77
8.6
02
77
8.8
03
77
8.8
55-2G24 55-2G2 55-2G3
19
77
8.8
FIGURE 7 - Typical Three Pole Mercury Contactor
Series
BF
BF
BF
BFC
BFC
BFC
04
77
8.8
55-2G19 55-2G4
22
No. of
Poles
1
2
3
1
2
3
Holding Coil Data
Inrush
VA
9.0
18.0
38.0
10.0
25.0
40.0
Holding
VA
6.0
12.0
25.0
6.5
13.0
28.0
gives for longer life of the control. The heater
elements
are
controlled
simultaneously,
no
sequencing of steps, which means there is no
possibility
of
air
stratification.
Several
slave
controls can be used with one master control
and thermostat.
B - Description: These UL listed solid state
proportional
controllers
consist
of
a
triac
assembly mounted on a heat sink.
These specially designed SCR's have the triac
assembly mounted inside the terminal box and
the heat sink is attached to the outside of the
terminal box. The heat sinks are in the open air
where there is good convection cooling, keeping
the inside of the terminal box at a normal
temperature.
Inducto
heaters
with
built-in
SCR's can be used with the air entering on either
side.
A special UL listed solid state thermostat must
be furnished when ordering any combination of
SCR's. Power output is controlled from 0 to
100% and is infinitely variable in direct
proportion to thermostat output. All elements
in the heater are controlled simultaneously
avoiding problems of air stratification.
Page 22 - ELECTRICAL DESIGN
5 - Fan Interlock Options: Effective January 30,
1974, all Inducto heaters must be furnished
with a type of fan interlock. The Inducto
standard will be a differential pressure switch.
A - Differential Pressure Switch. (Standard): The
differential pressure switch is available built-in
to the terminal box compartment UL approved.
This has become a very popular method. This is
an excellent application when constant fan is
used.
B - Electrical Interlock: A one pole contactor
interlock will be built in, wired to energize the
fan circuit when the first stage of the heater is
energized. (See wiring diagrams number E2-A, B
& C). For pricing refer to Pricing Section.
FIGURE 8
Typical Differential Pressure Switch
Thermistor Type Thermostat
6 - SCR Controllers
A - Application and Advantages: These solid
state proportional controllers are ideal for
application in schools, libraries, offices and
hospitals where noise is a factor. Since they are
all solid state there are no moving parts, which
C - Thermostat: A wall mounted vertical or
horizontal
thermistor
type
thermostat
model
701-1 with manual "On" and STBY (stand-by)
must be used with each Master SCR. Thermostat
range is 65°F to 85°F proportional band is 2°F.
(Full heat demand will actuate on a 2°F change.)
Any smaller change will cause a proportionately
smaller SCR output. Accuracy of thermostat is -±
1°F.
Remember:
No
other
commercial
thermostat can be used.
For
applications
thermostat
or
a
factory.
requiring
either
a
duct
pneumatic
system,
consult
D - Safety Contactor: Safety contactors UL
listed must be installed in front of and in line
with the SCR's unless the automatic reset
thermal cutout can carry the load. All three
phase heaters must be furnished with a safety
contactor.
FIGURE 9
Duct Heater SCR - (Solid State)
23
Any single phase heater exceeding the following
ratings must have safety contactors.
AUTOMATIC
2.5KW @ 277V, Single Phase
THERMAL CUTOUT 2.5KW @ 240V, Single Phase
R ATINGS
2.1KW@ 208V,Single Phase
1.8KW@ 120V, Single Phase
Control Voltage: This SCR system generates its
own control voltage for operation of thermostat.
Safety contactors holding coils can be operated
direct from line voltage up to 277 volts, single
phase when 480 volt three phase is required a
step-down transformer must be furnished.
7 - Disconnect Switches: The National Electric
Code states that there must be a disconnecting means
at or within site of the controlling means.
Disconnect switches can be field supplied or can be
built into the heater integral control panel or remote
control box.
We offer two types of disconnect switches. Door interlock type (fig. 11) or toggle type without door interlock
(fig. 11 a). Both devices meet the requirements of the
N.E.C. Door interlock switches are snap-action type
with the operating handle mounted in the hinged
cover and interlocked to open only when in the off
position. Toggle type switches are mounted on the
side of the control panel and kills all power in the
heater when in the off position.
8
Micro
De-energizing
Switch:
Electrical
de-energizing switch for control circuit. Plunger
type switch wired into control circuit of heater
to automatically de-energize the control circuit
when door is opened. Switch is single pole
double throw rated at 15 amps up to 480 v
non-inductive; 1/8 HP at 125 volts, 1/4 HP at
240 volts inductive. Alternate switch is available
for line volts over 480. Switch is rated at 10
amps up to 600 volts non-inductive and 6 amps
at. 115 volts; 3 amps at 230 volts; 1.5 amps at
480 volts and 1.2 amps at 575 volts inductive.
Both UL and NEC require that the contactors be
the disconnecting type when this type of switch
is used. This switch does not serve as the
disconnect switch as required by the NEC.
FIGURE 12 - Typical Pressure Type Micro Switch
9 - UL and NEC Safety Requirements: (a)
Primary over-temperature protection (cutouts)
Standard Disc Type: As standard practice all
Inducto Duct Heaters incorporate, as part of the
basic heater, one or more disc type, automatic
resetting temperature limiting devices (Fig.
13).
When a higher than normal temperature
condition occurs within the heating area and the
bi-metal disc reaches 170°F. the cutout opens
de-energizing the heater. After cooling, the
heater is automatically energized to continue
service.
The limit control is a UL listed temperature
limiting component having passed the 100,000
cycles of operation test under 150% of full rated
load.
It may be wired in the power circuit of single
phase heaters not exceeding its rated capacity
and in the control circuit, for pilot duty, on
larger single phase and all three phase heaters.
The resistive rating is 25 amperes and the pilot
duty rating is 125VA at 120, 240 or 277 Volts
AC.
FIGURE 11 A • Typical Toggle Disconnect Switch
FIGURE 11 - Typical Disconnect Switch with Operating
handle.
24
(1) This type of secondary over-temperature protective
device has to be replaced to reactivate the heater
following correction of the problems discussed above.
Two types are available.
They may be wired in line (load carrying) up to their
rated capacity of 48 amps, using enough cutouts to
de-energize the heater. They may also be wired for
pilot duty using one for the entire heater to control
backup contactors which are independent of the
primary controlling contactors. (See backup contactors below.)
FIGURE 13 -Disc Type
FIGURE 14 - Capillary Type
Capillary Type Cutouts (Special): On heaters for
ducts exceeding 10 feet in width a capillary type
automatic resetting limit control is required. In
addition, if the duct is also over 40 inches in
height two are required. This device has a
capillary temperature sensing element which is
mounted along the heating element enclosure
giving protection across the entire width of the
duct. It will be used on smaller duct heaters only
when specified. The application and rating is
identical to the disc type described above. This
cutout is a "fail safe" type control.
For pricing of the capillary type limit control
see Pricing.
Secondary Temperature Limit Controls - Disc
Type (Replaceable) Wired in a power circuit on
single or three phase heaters to de-energize the heater
stage on over-heating. Rated at 48 AMP up to 600
volt. Temperature to open 210 degrees F.
(b) Secondary over-temperature protection
(backup system)
The edition of the NEC states in section 424-64
(second paragraph):
"In addition" (to the automatic primary limit
controls)
"an
integral,
independent,
supplementary control, or controllers, shall be
provided in each duct heater which will
disconnect a sufficient number of conductors to
interrupt current flow. This device shall be
manually resettable or replaceable."
The secondary protection (backup system) is
always set at a higher temperature (210°F) than
the automatic primary limit controls, therefore
it should only operate when both an
over-temperature condition occurs and the
primary system fails due to frozen contacts, etc.
Inducto Duct Heaters are available with the
following two systems, UL listed, to meet the
above requirements.
(2) Back up contactors with pilot duty manual reset.
Reset is wired in series with backup contactor to deenergize heater.
25
When backup and controlling contactors are
built-in, the stages may be grouped to a
maximum of 48 amps per circuit, before being
wired through the backup contactors. When the
stages are small enough to allow grouping into a
circuit of 48 amp maximum, fewer backup
contactors are required to de-energize the
heater.
EXAMPLE: A three phase heater with three
stages of 16 amp each will be grouped into one
circuit of 48 amps on the line side of the
controlling contactors and will require only two
contacts (50 amp size) on the backup contactor
to de-energize this heater.
The above procedure (grouping) will not apply
when it is specified that each stage is to be field
wired to a separate supply circuit.
For maximum KW per circuit (48 amp) see
Table 6.
NOTE: The maximum voltage allowed on the
manual resettable cutouts is 480 volt on the disc
type and 277 volt for the capillary type;
therefore on heaters using higher line voltages, a
separate voltage source for the backup control
circuit must be supplied. This may be either
from a built-in transformer or from a remote
supply and must be specified. Both UL and the
NEC require only de-energizing type contactors
for backup service.
For pricing of backup contactors refer to
de-energizing type contactor. Refer to Pricing.
Disc Type: This device uses a bimetal disc to
sense over-temperature conditions and is
mounted through the terminal compartment. It
is recommended for use on heaters to be
installed in ducts up to 10 feet in width.
HF series heaters are designed for manual
resettable disc-type cut-out (load carrying)
application. Available are one-pole and two-pole
manual 48 amp maximum rated to 600 volts
AC. The two-pole manual resettable will
accommodate 96 amp on single phase
application and 48 amp on three phase
application. For selection of manual resettable
disc-type cutouts, refer to pricing.
FIGURE 17 - Capillary Type Manual Resettable Cutout -
Capillary Type: This device is the ultimate in
over-temperature
protection
and
is
recommended to be used on all heaters over six
feet in "W" dimension. It is required on all
heaters
over 10
feet
"W"
dimension.
The
temperature sensing capillary is mounted along
the top inside of the element enclosure and
down stream from the elements; therefore, the
air
flow
direction
must
be
specified
when
ordering this unit. Normally only one of this
type cutout is used per heater. If the heater load
exceeds its rated capacity then the cutout
should be used for pilot duty in conjunction
with backup contactors.
Refer to Pricing.
Backup Contactors: When a capillary Manual
Resettable cut-out, described above, is to be used as
the secondary protection, and is not wired in the line
to directly de-energize the heater, then one must be
used, wired for pilot duty, controlling backup contactors. Backup contactors are in addition to, and independent of, the primary controlling contactor or
other device, and are controlled by the manual resettable cutout only. They are wired in the line to deenergize the heater when an over-temperature condition causes the manual resettable cutout to cycle off.
They may be either built-in or remote.
NOTE: Backup contactors must be wired so they will
not cycle off and on by the thermostat.
FIGURE 18 - Typical Control Transformer
10 - Built-in Control Transformers:
When the control voltage is different
duct heater power voltage, a step-down
26
from
the
12 - Indicator (pilot) Light: Neon lights,
mounted through the front door panel of the
control box can be wired to indicate when:
(1) One stage is on
(2) Each stage is on
(3) An over-heating condition occurs.
Each light is marked as to the function it
indicates. For available circuitry see wiring
diagram numbers E7-A, B, C, D, E, and F. The
lights are mounted on the front door panel for
easy viewing and are available for 120, 208/240,
277 or 480 volts. Refer to Pricing.
transformer may be built-in to supply the
correct voltage thereby eliminating the task of
running a separate supply to the heater for the
control circuit.
The transformers are UL listed and are available
with primary and secondary voltages and sizes as
listed (Refer to Pricing). The VA rating required
for a given quantity of definite purpose type
contactors is also listed along with prices.
If controlling contactors are not built-in, both
the primary and secondary of the transformer
are wired to a terminal block for field
connection as required on the job. Unless
specified otherwise the primary voltage will be
the same as the heater power supply.
Either or both the secondary and primary can be
fused when specified.
If a manual resettable cutout and backup
contactors are being used and the heater line
voltage exceeds the voltage rating of the cutout
then the control transformers should be sized to,
carry both the controlling and backup
contactors or a separate supply furnished for the
backup control circuit.
Refer to Pricing.
11 - Time Delay Relays
When a positive time delay is needed between
the "on" cycle of consecutive stages to prevent
them from coming on simultaneously a time
delay relay is available built-in and factory
wired.
For control voltages of 24, 120, 208, 240 and
277 the 600 type is used, wired as shown in
diagram E5-B.
The 600 type gives approximately a 25 second
delay in the "on" cycle, but is wired to turn the
heat off immediately when thermostat is
satisfied, however a few seconds are required for
the delay relay to recycle off in order to repeat
the on delay sequence.
Refer to Pricing.
FIGURE 20 - Application of indicator light ana pilot switch.
13 - Pilot Switch: A single pole toggle switch is
available, which can be factory wired to prevent
operation of a heater stage or the entire heater
(see diagram number E8 A & B). The pilot
switch can be used in control circuits of 24, 120,
208/240 or 277 volts.
Note: Both UL and NEC require that
disconnecting type contactors be used when a
pilot switch is used. This pilot switch does not
serve as the disconnect switch as required by the
NEC.
Refer to Pricing.
FIGURE 19 - Time Delay Relay type 24A11. Switch rating 25
amp, 250 voltage maximum. Timer draws .15 amp for anticipator setting.
FIGURE 21 -Pilot Relay
Rating: 8 Amp resistive; 3 Amp at 125 volt and 1.5 amp at 250
volt inductive.
27
14 - Pilot Relay: In some cases when using a 24
volt control system the VA load of several heavy
duty contactors may exceed the capacity of the
thermostat or the low voltage transformer. In
such cases a pilot relay can be built in,
controlled by the 24 volt circuit to switch line
voltage (250 volt maximum) which operates the
heavy duty contactors.
Refer to Pricing Section.
15 - Pneumatic-Electric (P.E.) Switches: When a
pneumatic-control system is used, P.E. switches
are required to control the heater directly (load
carrying)
or to
operate the controlling
contactors of the duct heater (pilot duty). The
P.E. switches, may be built in and factory wired.
Inducto offers a number of P.E. switches that
can be purchased and installed from our own
stock. This application is UL approved and
carries the standard one year warranty. Refer to
Pricing Section.
16 -Step Controllers - Built in or remote.
A - Electric Step Controllers: This built-in
modulating electric step controller was developed
especially for use in duct heaters and has a 150ºF
ambient temperature rating. Standard time cycle for
10 switches to come on is 13 minutes. Built-in
recycle relay prevents entire load from coming on
at once after power failures. Switches are rated for
pilot duty only (up to 240V) and must be used to
control contactors. Specify holding coil voltage of
120V, 208V or 240V. For 480V line voltage
applications, specify a 480V/120V transformer.
Built-in transformer provides 24V for thermostat
circuit only not for contactor holding coils. Minimum
terminal box height is 12". Use T921A or T991A
thermostat or equivalent.
Should power for the step controller be furnished
from the duct heater control transformer add 25VA
to the required transformer capacity.
NO.
STEPS
CATALOG
NUMBER
NUMBER OF
STEP CONTROLLERS SUPPLIED
2-5
S984D1023
1
6-10
S984F1018
1
11-15
S984J+S984D
2
16-20
S984J+S984F
2
FIGURE 22-A Typical P.E. Switch
A common practice has been for the controls
contractor to send the switches to the factory
for wiring and mounting. This leaves only the
tubing connections and adjustment to be done
in the field. P.E. switches supplied by others are
not covered in the Inducto warranty, but if
selected from the following list the heater will
bear the UL label. Check the factory for
additional listing.
Perm Controls
Model 6270, 6272, P10-BC,-BH,-FC, P67-AA,
-CA, -EA, -FA
Honeywell
Model P658-A, -B, Model L404-A, -B, -C, -D, -F,
P643A, P654A. L604A
Robertshaw
Model R423, R422, R424
Powers
Model 134-1450, 134-1451, -2, -4, -5, -6, 251
Johnson Service
Model G-270, -271, P7100, P7200, -7221
Mercoid
Model AP-2. .3. -4, -26, -36, -54. -153
Barber Coleman
Model PC-126,-127,-131,-132,-111,-141,-151
See wiring diagrams Figure E-6 for Pilot Duty
and E-27 for load carrying systems. Refer to
Pricing Section.
FIGURE 23 - Electric Step Controller
B - Thermostats
Suggested for use with above electric step
controllers.
ROOM TYPE
T921A
(Modulating)
FIGURE 24
Catalog
Number
T921A
28
Range
Voltage
56-84ºF.
24V
Only
Throttling
Range
V½ºF.
Type
Room
Catalog
Number
T991A
Range
Voltage
Throttling
Range
Type
0-100°F.
24V
Only
2½°F.
Duct
Electronic Step Controller 100% Solid State
Operation — Operation typical of temperature
regulation is as follows:
Heating: As the temperature drops below the setpoint, the first stage heating circuit is energized. If the
temperature continues to drop, the second, and subsequent, heating circuit(s) will be engaged. When the
temperature rises above the "pull-in point" for a stage,
that stage drops out. Time delay between stages
assures sequencing of stages, in order, regardless of
demand requirements. Sequencer re-programs to start
(deadband) on power failure.
Features
Solid
State
circuitry.
Printed
circuit
wiring
Automatic changeover between mode function
(heating
and
cooling)
Time delay between stages assures sequencing of
steps,
regardless
of
demand.
Re-programs to start through first stage on power
failure.
Thermistor sensing or 0-135 ohm input.
Wall thermostat may be horizontally or vertically
mounted.
Senor may be wall mounted, or remote mounted.
Remoted setpoint and/or sensor location available.
Setpoints and deadband field adjustable.
Unlimited selection of differential between stages and
deadband range features.
SPECIFICATIONS/ELECTRICAL
Input Voltage
19.-29 VAC
Current (Logic)
150 MA
Current (Load)
1 Amp/Stage
Furnished w/ 4½" bulb + 60" capillary tubing
C - Pneumatic Step Controller: These step
controllers are used for sequence control of
electric duct heaters and other devices.
The basic unit consists of a series of switches,
cam operated by a common drive shaft, driven
by a pneumatic actuator, all mounted on a
common base. The switches are enclosed with a
metal cover. An external pointer indicates the
shaft position thru 180° from full "on" to full
"off".
Switches are factory set for normal operation
and cams can easily be field adjusted. Switch
differential is fixed with 5 angular degrees
minimum. The switch rating is 20 amperes at
120, 250 and 480 volts AC, 1 HP at 125V and 2
HP at 250V.
The power required for the SP-300 series or
equivalent is 0-15 PSI air supply. Typical
pneumatic thermostats are available to operate
this controller.
For pricing see Pricing Section. Check the
factory for additional listing.
Output Voltage
Current
Range
of
Setpoint
Range Limits
Same as input
1 Amp/Stage
20 °F
0°to125°F
THERMISTOR INPUT
Adjustment/Settings
Factory Min.
Max.
Deadband
2°F
1°F
15 °F
Pull-in between
stages
1.5 °F 0.5 °F 6°F+
Hysteresis (pull-in/
drop out)
1.0°F Not field adj.
0-135 OHM INPUT
Adjustment/Settings (On Application,
consult factory)
Operating Temperature - 15°F to 140°F
Input Signal
Standard
10K
Optional ("A" suffix) 0-135 ohm
FIGURE 26
Pneumatic Step Controller
29
- CONTROL THERMOSTATS -
CATALOG
NUMBER
TYPE
TEMP.
RANGE
VOLTAGE
AMPERE
RATING
STAGES
NO.
ACTION
1A22
Room
50-90ºF
125-250277V.
22
1 HT.
Bimetallic
TJT-120
Room
60-90ºP
24V.
—
1 HT.
Bimetallic
1F30-910
Room
45-90ºF
25V
1 HT.
Mercury
Adj. Anticipator
0.15 to 1.0 A.
½ º Differential
IF 56-301
Room
45-90ºF
25V
—
1 HT.
Mercury
HTG.Adj.: 0.15 to 1.0A.
Cooling: 0 to 1.5 A.
1C71-51
Room
HT-50-85ºF
CL55-90ºF
25V
—
2HT.
1CL.
Mercury
HTG. Adj.: 0.15 to 1.0A.
Cool Fixed: 0 to 1.5 A.
1C72-101
Room
50-85ºF
25V
—
2HT.
Mercury
Adjustable 0.15 to 1.0A
T675A1417
Duct
55-175ºF
120-240V
8 A.@ 120V
5.1 A.@ 240V
1 HT.
Hydraulic
5' Copper Capillary
½ x3-9/16 Bulb
Adj. Diff.: 3.6 to 12ºF
T675A1029
Outdoor
Bulb
0-100ºF
120-240V
8A@ 120V
5.1 A @ 240V
1 HT.
Hydraulic
M7M
Room
35-90ºF
125-250277V
22A@ 125-250V
18A@277V
2HT.
Bimetallic
M7M-TP
Room
35-90ºF
125-250277V
Ditto
2HT.
Bimetallic
M7-TP
Room
35-90ºF
125-250277V
Ditto
1 HT.
Bimetallic
TC-282
Remote
Bulb
10-90ºF
24-240V
12A@ 120V
6 A @ 240V
1600VA
3 SPDT
Hydraulic
Adj.Diff. 2-7ºF. Bet.
Stages 0-20ºF
6' Cap. Lockable Knob
L6018D-1004
Remote
Bulb
55-85º F
Ditto
2 SPDT
Hydraulic
Stage Diff. 2ºF.
Interstage Diff. 4½ºF,5½' Cap.
T42H-1081
Room
40-80ºF
Ditto
2 HTG.
Mercury
Stage Diff. 1ºF.Interstage Diff. 1-5ºF.
T42M-1031
Room
40-80ºF
Ditto
3 HTG.
Hydraulic
Stage Diff 2ºF,Interstage Diff. 2ºF.
8A @ 120V
5.1 A @ 240V
1600 VA
1 A ® 240V
0.5 A @ 240V
Ditto
1A22
FEATURES
Load Carrying
Snap Action
Adj. Anticipator
0.3 to 1.0 A.
20' Copper Capillary
½ x 4-3/16 Bulb
Adj.Diff.: 3 to 10ºF
½ºF Diff.
1½º Bet. Switches
½ºF Diff.
1½º Bet. Switches
Tamper Proof
½ºF.Diff.
4 to 6 cycles/hour. Tamper Proof
TJT-120
1F30-910
T675A-1540
T675A-1565
L6018D-1004
1C71-51
1C72-101
1F56-301
M7M
M7M-TP
M7-TP
TC-282
T42M
T42H
30
E - REMOTE CONTROL PANELS
In some applications the required components
cannot be built in the duct heater terminal box
because of space limitations, inaccessibility, etc.
In this case some, or all, of the components can
be mounted and factory wired internally, as
applicable, in a panel for remote mounting. All
terminals are marked to clearly indicate the field
connections between the panel and the heater.
The panel is of the same construction as the
heater terminal box and the same components
will be used as previously described in this
catalogue for use in the Raywall duct heater.
The required controls are controlling contactors,
overcurrent protection, back up contactors (if
used as the required backup system), and all
must be supplied by the heater mfg. as required
by UL and NCC.
Heater and
panel will be completely
coordinated,
ie:
circuit
sizing,
terminal
markings, etc., and a wiring diagram provided
showing inter connections between components.
The panel will be UL listed with the same
controls and combinations as the heater with
integral controls.
Components that may be installed in remote
panels are as follows:
Controlling contactors
Backup contactors
Transformers
SCR units
Fusing or circuit breakers
P.E. switches
Disconnect switches
Pilot lights
Pilot switches
Step controllers, program switches
FIGURE 27
A Typical Remote Panel
31
COPYRIGHT 1983 INDUCTO/MARKEL PRODUCS CO.
32
EEF
FORM #C91181
Heater
Tag
Qty.
Model
No.
Total
Kw
POWER
Volts
Phase
Control
Circ.
Volts
No.
Of
Stages
KW
Per
Circ.
Direction
Of
Air Flow
Insert Flange
Capillary Automatic Reset
H
Not approved
Approved as noted
Approved
_______________________________
_______________________________
_______________________________
_______________________________
_______________________________
_______________________________
NOTES:_________________________
REMOTE CONTROL ENCLOSURE
Fusing
Fusing Dual Element
Circuit Breaker
Fused Disconnect Switch
Unfused Disconnect Switch
Dust Proof Enclosure
80/20 'A' Elements
Derated Elements
Protective Screen
Time Delay
Cover Interlock Switch
Pilot Lights
Pilot Switch
Internal Duct Insulation ____ inch
Aluminized
BOTTOM INSERT CONTROL BOX
De-energizing Contactor
Disconnecting Contactor
Mercury Contactor
Electric Step Controller
Pneumatic Setp Controller
SCR Controller
P.E. Switch
Transformer w/pri. Fusing
Transformer w/pri. & sec. Fusing
Differential Pressure Switch
Fan Interlock Relay
Replaceable Over Temperature Protection Disc Type
Capillary Manual Reset
CHECK AS REQUIRED: INTEGRAL
(Installed only when specified)
W
Healer Type Duct Size
The following information is required: Quantity, KW, voltage, phase, number of circuits, controls and control volts, metal to metal duct size.
Item
INDUCTO DUCT HEATER SUBMITTAL
OPEN COIL
* * 'E' DIM. IS STANDARD 4½ " or 6 "½MAX. o r 9 ½" MAX. FOR DISCONNECT SWITCHES
CONTRACTOR_____________________________________
ENGINEER ________________________________________
ARCHITECT _______________________________________
CUSTOMER _______________________________________
PROJECT_________________________________________
AGENT___________________________________________
INDUCTO/MARKEL INDUCTO HEATERS
MARKEL PRODUCTS COMPANY
JOHNSON CITY, TENNESSEE 37601
C
B
A
1. M, B, C, A. E, D, F, and G
dimensions depend upon the
heater design and will be
determined by the factory. If any of
these dimensions are critical, they
must be specified under "Notes".
2. All heaters are furnished standard
with Disc Type High Temperature
Cut Outs (HTCO), Wiring and
Terminal Strips.
3. Control panel extends on entering
airside of element frame unless
otherwise specified.
4. Advise details of duct insulation,
Thickness, internal, external, etc.
M
*Heatd
Page 31
Page 80
Markel
Products Company
Commercial Division
P.O. Box T CRS
Johnson City, TN 37601
615/282-5440
ORDER AND PRICING
FORM 93061
P.O. DATE:___________________
PRICED BY:__________________
PAGE____OF___
INVOICE
SHIP TO
P.O. NUMBER ____________________________________
TAG JOB: ________________________________________
TAG
TAG
ITEM: _________ QTY. ____
_________
_________
ITEM: _________ QTY. ____
_________
_________
TOTAL KW _______POWER VOLTS_______PHASE_______
CONTROL VOLTS______________ NO. OF STEPS________
HEATER TYPE _________________ I = INSERT F = FLANGED
DUCT SIZE W____ x H_____ OUTSIDE DIM.
TOTAL KW _______POWER VOLTS_______PHASE_______
CONTROL VOLTS______________ NO. OF STEPS________
HEATER TYPE _________________ I = INSERT F = FLANGED
DUCT SIZE W____ x H_____ OUTSIDE DIM.
IF INTERNALLY INSULATED DUCT, DUCT LINER THICKNES = _______
IF INTERNALLY INSULATED DUCT, DUCT LINER THICKNES = _______
AIR FLOW DIRECTION
AIR FLOW DIRECTION
"R" = LEFT TO RIGHT UP
"L" = RIGHT TO LEFT DOWN
SPECIAL INSTRUCTIONS ______________________________
____________________________________________________
____________________________________________________
"R" = LEFT TO RIGHT UP
"L" = RIGHT TO LEF T DONW
SPECIAL INSTRUCTIONS ______________________________
____________________________________________________
____________________________________________________
_______ KW @ ________ VOLTS ____ PHASE = ______
_______ KW @ ________ VOLTS ____ PHASE = ______
TOT.AMPS
TOT.AMPS
_____ (____KW) STEPS @ _____ AMPS PER STEP
_____ (____KW) STEPS @ _____ AMPS PER STEP
WATTS DENSITY = ____________ KW/FT2
WATTS DENSITY = ____________ KW/FT2
LIST
HEATER BASE W _____ + H_____ = _____@ $_______
LIST
HEATER BASE W _____ + H_____ = _____@ $_______
MODEL ADDRESS
MODEL ADDRESS
KEY NO.
KEY NO.
_____________
___________ = _______
_____________
___________ = _______
_____________
___________ = _______
_____________
___________ = _______
_____________
___________ = _______
_____________
___________ = _______
_____________
___________ = _______
_____________
___________ = _______
CONTROL
OPTION
KEY NO.
72-____
73-____
76-____
78-____
QTY
(
)
(
)
(
)
(
)
________
(
) ______________________
_______ = _________
________
________
(
(
) ______________________
) ______________________
_______ = _________
_______ = _________
________
________
________
(
(
(
) ______________________
) ______________________
) ______________________
_______ = _________
_______ = _________
_______ = _________
DESCRIPTION
PRODUCT OF AIR FLOW__
LIST
EACH
$______ = ________
CONTROL CHARACTORS_ $______ = ________
CONTROL TRANSFORMER
$______ = ________
BRANCH CIRCUIT FUSING
$______ = ________
LESS __________ %
HEATER LIST PRICE EA. $_______
X COST MULTIPLIER ________
HEATER NET PRICE EA. $______
CONTROL
OPTION
KEY NO.
72-____
73-____
76-____
78-____
QTY
(
)
(
)
(
)
(
)
________
(
) ______________________
_______ = _________
________
________
________
(
(
(
) ______________________
) ______________________
) ______________________
_______ = _________
_______ = _________
_______ = _________
________
________
(
(
) ______________________
) ______________________
_______ = _________
_______ = _________
DESCRIPTION
PRODUCT OF AIR FLOW__
$______ = ________
CONTROL CHARACTORS_
$______ = ________
CONTROL TRANSFORMER
$______ = ________
BRANCH CIRCUIT FUSING
LESS __________ %
33
LIST
EACH
$______ = ________
HEATER LIST PRICE EA. $_______
X COST MULTIPLIER ________
HEATER NET PRICE EA. $______
Page 32
INDUCTO DUCT HEATER
SUGGESTED SPECIFICATIONS
2. Ceramic coil supports to be floating, but contained,
and easily replaceable.
3. Ceramic coil insulators to be on staggered spacing per
rack to eliminate blank areas in the air pattern thru the
heater, and provide uniform heating over the entire
cross section of the element.
4. Racks to support element coils on no more than 3 ½ "
centers.
General
1. Provide Series "HF" Inducto, open coil, electric duct
heaters, as manufactured by Markel Products Co. and
as listed in the schedule.
2. Power voltage and phase, control voltage, wattage,
duct size, number of steps to be as per schedule.
3. Heaters to be either Slip-in or Flanged type as called
for.
4. Three phase heaters shall have balanced three phase
steps unless specified otherwise.
5. All heaters to be UL listed for zero clearance to combustible surfaces and bear the UL label.
6. All heaters shall meet the requirements of the latest
National Electric Code.
7. Standard terminal box, recessed terminal box, standard control cabinet, remote control cabinet as well as
element housing and racks all to be made of heavy
gauge galvanized steel. (Aluminized steel optional.)
8. All heating coils to be made of high grade
nickle/chromium resistance wire and terminated by
means of a loop of wire being sandwiched between
stainless steel or nickle plated washers and terminal
hardware. All terminal hardware to be insulated from
the heater by a two piece ceramic bushing.
Terminal Box or Control Cabinet
1. Shall be constructed of heavy gauge galvanized steel
(aluminized optional) and in sizes up to 18" x 18"
shall be No. 20 gauge and over to be No. 18 gauge. All
boxes to have a solid cover, of the same gauge, complete with a piano type hinge on the longest side, approved tool operated latch and pull ring. Covers over
48" long to be provided with two latches and pull
rings.
2. Insulation consisting of ½ " high density fiberglass will
be provided, attached to the cabinet, between the
cabinet and the heating section.
3. Recessed terminal boxes used when ducts are internally insulated, or in air handling units, to be of the
same general construction as item 1 above.
Airflow Direction
Heaters will be interchangeable for mounting in a
horizontal or vertical duct except when position sensitive
mercury contactors, SCR's or capillary type limit controls
are built-in. In these cases, airflow direction must be
specified.
Element Assembly
1. To be of "Modular" design with each module independently and easily removable from the terminal
box or control cabinet.
2. Each module to contain no more than 2 layers of element coils so that any one coil may be replaced
without disturbing others.
3. Element coils of each module to be on staggered spacing so that all coils per module will be in the air stream,
and shadowing (overheating) and/or blank areas
eliminated.
Safety Controls
1. Primary over temperature protection shall be provided
by built in disc type automatic reset thermal cutouts
for duct heaters up to 10' in width. Heaters over 40"
high require two cutouts. Capillary type automatic
reset thermal cutouts are required for any heater 10'
wide or over. Capillary type controls to be UL listed
and of the "fail safe" type.
2. Secondary over temperature protection shall consist
of a sufficient number of load carrying replaceable disc
controls to de-energize the elements if the primary
system fails.
Alternate A — One pilot duty manual reset and back
up contactors.
B — Replaceable heat limiters for single phase
heaters.
C — Bottom insert type heaters require a capillary
type manual reset and back up contactors.
Capillary type manual resettable cutouts are required for
all heaters 10' wide or over, recommended to be used on
all heaters over 6' wide, and must be of the "fail safe"
and "trip free" type.
Element Housing
1. To be of No. 18 Ga. galvanized (aluminized) steel and
to be of roll-formed construction with multiple brakes
and ribs for stiffness and rigidity.
2. Each housing module to be no more than 4¾ "wide
(in direction of air flow) and contain 2 layers of element
coils on staggered spacing. (2 mod. = 9 1/8")
Element Rack
1. To be constructed of No. 20 Ga. galvanized
(aluminized) steel and formed with multiple brakes and
ribs for stiffness and rigidity. Maximum individual rack
length to be 30".
34
SUGGESTED SPECIFICATIONS (CONT’D)
4, All manual safety devices shall be servicable thru the
terminal box without removing the heater from the
duct.
3. Overcurrent protection incorporating fuses or circuit
breakers must be provided for all heaters rated more
than 48 amperes, factory installed, within the heater
enclosure, or provided as a separate assembly by the
heater manufacturer. Heaters exceeding 48 amperes
total line current must be divided into subcircuits (as
allowed by stages) of less than 48 amperes and be
protected at not more than 60 amperes. The main conductors supplying these overcurrent protective
devices are considered branch circuit conductors and
are subject to the 125% ampere rating rule of NEC.
Wiring Diagrams
1. A separate, complete and specific wiring diagram shall
be permanently attached to each heater. Typical wiring diagrams are not acceptable.
2. Control and line terminals in each heater shall be
marked identical to the wiring diagram.
3. Additional diagrams, instructions, etc., to be firmly
held in position by a metallic snap clip or pocket inside
the cover.
Available Built-in Components
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
Disc type automatic high temperature cutouts.
De-energizing break magnetic contactors.
Replaceable Thermal Cutoff (disc type).
Load carrying manual reset high temperature
cutouts, disc type, and backup contactor.
Non-fused disconnect switches.
Class H, one time fuses 125% rated per the NEC
except:
a. line fusing for a bottom insert type construction
must be in a separate remote box..
b. Circuits in a remote box cannot be group fused,
each circuit must be fused separately.
SCR Controls.
Load carrying P.E. switches.
Transformer with fusing per UL requirements.
Electric or pneumatic step controllers.
Differential pressure switch fan interlock.
Time delay between stages.
Indicator pilot lights, first stage on.
14. Pilot switches.
15. Cover interlock switch, pilot duty.
16. Pilot relays.
1 7 . Capillary type automatic high temperature cutouts.
18. Disconnecting break magnetic contactors.
19. Mercury contactors -de-energizing, disconnecting.
20. Capillary type manual reset high temperature
cutouts.
21. Manual reset high temperature cutouts pilot duty and
back-up contactors.
22. Fused disconnect switches.
23. Circuit breakers.
24. Dual element fuses.
25. Transfomer: class II integrally protected, secondary
fused.
26. Electrical fan interlock.
27. Indicator pilot lights, each stage on, panel energized,
etc.
Other Optional Features
1.
2.
3.
4 . Dustproof terminal box, control cabinet.
5 . Remote control cabinet, standard, dustproof.
6. Bottom insert construction.
7 . Dual terminal box construction, flanged, insert.
8. Terminal box overhang on, downstream side, top,
bottom.
Aluminized terminal box, control cabinet, heater element assembly. For stainless steel construction consult factory.
Protective screens, inlet side, outlet side, both sides.
Flanged heater frame for plain ducts or internally insulated ducts.
35

open coil duct heaters

Transcription

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