Fire Survival Cable: Understanding of Lab Scale to

FIRE SURVIVAL CABLE: UNDERSTANDING OF LAB SCALE TO
MANUFACTURING SCALE CABLE VALIDATION
Sathish kumar Ranganathan, Tim Waters, Jon Malinoski, Srinivas Siripurapu
General Cable Indianapolis Technology Center, Indianapolis, IN
Aparna M.Joshi, Ninad M.Joshi; K. D. Joshi Rubber Industries Pvt. Ltd., Pune, India
Abstract
In order to successfully develop fire survival cable
products it is important to have a good understanding
of the relationship between lab scale material
development testing and production-scale cable
capability. Research and development work on fire
survival cables has been active for more than a
decade and today many commercial products exist in
the market for these applications. However each fire
survival cable design, application type and testing
protocol is designed to be different to meet specific
regional standards and customer requirements. In
this work, we have demonstrated lab scale
understanding of ceramic formation in silicone
compounds and translated to large scale IEC 6033121 fire survival cable test validation, while also
meeting other electrical, mechanical and heat ageing
requirements.
Introduction
Fire survival cables are designed to protect people
and properties in many critical safety applications
such as security alarms, emergency lights,
communication systems [1] in in locations such as
oil and gas infrastructure, hospitals, and commercial
buildings [2]. These cables are an important and
growing market opportunity within the wire cable
industry.
For fire resistant cables, customer requirements,
application type, and standards dictate the final cable
design and material type used in cable construction.
These cable design and test standards are region
specific; hence it is required to meet a specific fire
test method, electrical, mechanical and physical test
requirements. There are different types of cable
designs being used for fire survival cable
applications such as MC-HL, RHW, RHH and
others. Each cable type may be rated for different
electrical properties like UL 44 wet or dry rating and
cable fire rating IEC 60331-21, and UL 2196.
Developing appropriate insulation and jacket
compounds to pass these cable requirements is a
challenging task, since there are many complex
material parameters such as ceramic type, hardness
of the char, dimensional change, smoke release and
in-cable use of mica tape in cable [3] design that
must be considered. The fire survival test is designed
to verify that the cable is capable of performing in an
emergency condition and meets the specific test
standard. However in reality most of these cables
will never experience an emergency situation. Hence
while designing insulation and jacket compounds,
cable application properties need to be considered.
Balancing cable application and emergency
condition requirements is a particular challenge for
wire and cable materials development, in particular
for the polymeric insulation which must convert to a
ceramic form in order to pass a fire survival cable
test.
For more than a decade silicone resins have been
used as the basis for ceramifiable silicone
compounds, since it has advantage of forming silica
after burning. There are several different types of
silicone resins used in cable applications with
different curing mechanisms such as free radical,
addition and condensation. Though silicone-based
compounds provide excellent flexibility, long term
heat ageing resistance is often a challenge for these
materials. A critical determinant for ceramic
formation is the type of filler used in the compound.
There are many different types of filler approaches
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currently used in industry such as glass frit, Mica
[4], calcium carbonate [5], montmorillonites [6],
APP [7] in order to achieve ceramic char formation.
However each mechanism has its own advantages
and disadvantages when considering final cable
properties including wet electrical insulation,
ceramic formation and compound melt process
ability. In this work we have demonstrated a method
to screen ceramic formation on a lab scale and then
correlate these results to manufacturing scale fire
survival cable testing.
Experimental: Lab Scale Development
Polymeric materials and fillers are used in these
experiments are SILASTIC® NPC-40 Silicone
rubber from Dow Corning; Teco-sil® Fused silica
from C-E Minerals; glass frit powders are used from
Furtura, ABX and KATI; Vinyl silane from Evonik
chemicals; Mica from LKab Minerals, Zinc Borate
from Chemtura and Aluminum Trihydroxide from
Huber. The experimental insulation compounds
were mixed in roll mill at 80°C for 10 minutes and
70 mil plaques were molded under pressure at 150C
for 20 minutes to measure mechanical and ceramic
properties.
Ceramification properties were screened by the
following test method: Two inch square, 70mil
plaque dimensions and weight were measured before
and after the furnace test, which is performed by
hanging the samples in an 800°C furnace for 2
hours. The changes in dimension are reported as
percentage change and weight retention or char
formation is reported as char content percentage. The
formulation design details and ceramification test
results are disclosed in Table -1 and Figure - 2. The
composition with fused silica and mica with other
ingredients but not with glass frit powder forms a
ceramic, however it does not gives the sufficient
strength after furnace test to form ceramic selfsupport. Addition of different types of glass frit
powders helped to increase the char strength and
ceramic char to have self-support after the furnace
test. The other aspect is changes in dimensions were
measured and calculated the average percentage in
dimensions before and after furnace test. Sample
with Glass frit KATI shows the lowest average
dimensional change after ceramification test. The
insulation compound which has the limited
dimensional changes or low expansion expected to
have less stresses between other layers in the cable
and will low possibility of cracking while fire
survival test.
Manufacturing Scale Validation
Based on the lab-scale screening results and
learnings, the best performing ceramifiable
insulation compound was scaled up in manufacturing
plant for cable construction and testing. 18AWG and
45 mil thickness insulation wires were made using a
continuous vulcanization process and were
subsequently braided with glass tape. The braided
insulation core was then used for further cable
construction which includes application of fillers,
binder tape, aluminum armor and Jacket as disclosed
in Figure-1. The manufactured cable was validated
for IEC-60331-21 fire survival test protocol and
other insulation performance requirements as per
EM60 short term electrical test method and
mechanical and heat ageing properties were tested as
per UL 1309 protocol. The results are reported in
Table.2. The ceramifiable insulation compound
meets the short term electrical requirements and long
term heat ageing requirements.
Fig-1: Fire survival MC-HL cable design
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IEC 60331-21 Fire Survival Test on MC-HL cable
The completed MC-HL cable was exposed to the
circuit integrity fire survival test as per IEC60331-21
procedures. Initially the cable is conditioned at least
16 h at 20 ± 10 ºC and placed in the test fixture as
shown in Fig- 3a. The cable was charged with 600V
electrical current before initiating the flame. Once
flame is applied on the cable (Fig.3b), the circuit
integrity is monitored. The cable is expected to pass
the requirements for at least 90 minutes time period
and 15minutes continue to energize till flame has
been extinguished. If the cable is unable to maintain
circuit integrity it is considered a failure per the IEC
60331-21 fire survival test. This test is designed on
the assumption that in a real life fire emergency
situation, these cables need to remain in operating
condition in order to power emergency lights and
systems and improve overall fire survivability.
Figures 3c, 3d, and 3e show passing results of the
IEC 60331-21 fire survival test after 180 minutes
exposure to 750-800°C flame.
Summary and Path forward
Understanding ceramic formation and dimensional
changes is an important factor in order to pass large
scale fire survival cable validation testing. Silicone
based ceramifiable compounds can be designed to
meet the short term electrical and long term heat
ageing requirements and pass the IEC 60331-21 fire
survival test requirements. However, several other
limitations need to be considered while using
silicone based ceramifiable insulation compounds to
manufacture fire survival cable. Though silicone
based compounds provide excellent ceramic forming
properties, manufacturing scale handling of silicone
material require specific considerations such as
method of feeding compound to the extruder and
extruder screw type. In addition, silicone compounds
typically are not capable of meeting long term wet
electrical insulation property as per UL 44 which is
essential for UL 2196 fire survival test certification
in North America. Further research work is in
progress to address the above mentioned challenges
by using silicone blends, copolymers and other
olefin resins.
Acknowledgements
Authors would like to share their credits, thanks
and acknowledgements to General Cable
Indianapolis Technology Center Technicians &
Process Team, Willimantic lab, Engineering and
Manufacturing Team, General Cable Manlleu
Spain test lab for their contribution, dedication
and support to this project.
References
1. Ceramifiable Composition for Power and/or
Telecommunications cables; Martinez Agea Juan De
Dios, Barbeta Estrada Javier, Calveras Ibanez
Daniel, Garcia Lopez David, Poveda Bernal Jesus
and Alonso Sastre Carlos WO2013093140 (A1)
2. Staszewski, Zygmunt; Protecting life safety
circuits in high rise buildings, Electrical
Construction and Maintenance, Jul, 1, 1995
Thermal stability and flammability of silicone
polymer composites, Hanu, L.G.; Simon, G.P.;
Cheng, Y.-B.; Polymer Degradation & Stability,
2006, Vol.91 (6), p.1373-1380
3. Testing of the fire-proof functionality of cable
insulation under fire conditions via insulation
resistance measurements; Polansky, R; Polanska, M
Engineering Failure Analysis, 2015 Nov, Vol.57,
pp.334-349
4. Preferential orientation of muscovite in
ceramifiable silicone composites; L.G. Hanu, G.P.
Simon, Y.B. Cheng∗; School of Physics and
Materials Engineering, Monash University, Clayton,
Vic. 3800, Australia ( Mica) Materials Science and
Engineering A 398, 2005, p.180–187
5. An experimental design approach in formulating a
ceramifiable EVA/PDMS composite coating for
electric cable insulation; E.E. Ferg*, S.P. Hlangothi
and S. Bambalaza; Polymer composites, 24 JUN
2015.
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6. Influence of surface-modified montmorillonites
on properties of silicone rubber-based ceramifiable
composites; Anyszka, R. ; Bieliński, D. ; Pędzich,
Z.Szumera, M. Journal of Thermal Analysis and
Calorimetry, 2015, Vol.119(1), pp.111-121
7. Ceramifying composition for fire protection;
Graeme Alexander, Yi-Bing Cheng, Robert Paul
Burford, Robert Shanks, Jaleh Mansouri, Kenneth
Willis Barber, Pulahinge Don Dayananda Rodrigo,
Christopher Preston Olex Australia Pty Ltd;
US8409479B2
Part-A: Lab Scale Testing
Table-1: Ceramifiable Insulation Compound
Ingredients
T1
phr
100
T2
phr
100
25
T3
phr
100
T4
phr
100
NPC 40 - Silicone
Glass Frit Powder ABX
Glass Frit Powder Futura
Glass Frit Powder KIAT
Fused Silica
Vinyl Silane
Mica
Zinc Borate
Antimony oxide
Peroxide
Total
50
2
20
10
10
0.6
192.6
50
2
20
10
10
0.6
217.6
50
2
20
10
10
0.6
217.6
25
50
2
20
10
10
0.6
217.6
Properties after furnace test
Char content %
Ceramic formation
Length %
Width %
Thickness %
Average change %
T1
47
Weak
N.T.
N.T.
N.T.
N.T.
T2
63
Hard
-4.73
7.97
20.2
7.81
T3
65
Hard
-2.57
6.2
12.1
5.24
T4
64
Hard
-1.2
2.64
13.1
4.85
25
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Tested on Extruded Wires
Cable
Requirements
Units
Ceramifiable
Compound
Electrical Properties ( UL 44- EM 60)
Dielectric constant
1 day
<6
4.8
Dielectric constant
1 to 14 days
< 10 %
1%
Dielectric constant
7 to 14 days
< 3%
1.02%
14 days
1
0.64
4000
6093
stability factor after ( 90 Deg. C)
Insulation resistance IRK, Ohmsmeter/1000 Ft. ( 15 Deg.C)
Mechanical Data ( Un-aged)
Tensile strength
PSI
800
1315
Elongation
%
250
361
Tensile strength
%
65
98
Elongation
%
50
80.5
Heat Ageing Retention, (158C @ 168 hours)
Heat Ageing Retention (108C @ 500 hours)
Tensile strength
%
65
Fig.2:
Lab furnace ceramifiable
Elongation
% test (800C for502 hours)
IEC 6033-21 test at 750 Deg.C
90 minutes.
Circuit integrity
94.1
76.4
Pass
Part-B: Manufacturing Scale Cable Validation
Table-2: Tested on 18AWG Copper wire and 45mil ceramifiable insulation compound
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Table-3: IEC 60331-21 Test Condition
IEC60331-21Test
Conditions
Units
Flame application time
90
Minutes
Flame temperature
750 ≤ X ≤ 800
ºC
Test voltage (AC 50 Hz)
600
V
Ambient temperature
5 ≤ X ≤ 40
ºC
Cooling period
≥ 15
Minutes
Requirements
Survival time
X ≥ 120
Minutes
Test observation
Survival time
180
Minutes
Fig. 3: IEC 60331-21 Cable Test: 3.a) Cable in test set-up before starting the test; 3.b) Test is in progress;
3.c) Before end of the test; 3.d) Electrical- Circuit integrity monitoring at 180 minutes; 3.e) Tested cable after
cooling
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