Ministry of Defence
Defence Standard 61-12 (Part 31)
Issue 2 Publication Date 20th January 2006
Wires, Cords and Cables,
Electrical – Metric Units
Part 31:
Sheaths - Limited Fire Hazard,
DEF STAN 61-12 Part 31 Issue 2
Contents
Introduction................................................................................................................................................................. v
1
Scope .............................................................................................................................................................. 1
2
Warning .......................................................................................................................................................... 1
3
Related Documents ....................................................................................................................................... 1
4
Definitions ...................................................................................................................................................... 2
5
Abbreviations................................................................................................................................................. 2
6
General Requirements for Sheathing Materials ......................................................................................... 3
7
List of tests and sample sizes...................................................................................................................... 3
8
Test Requirements ........................................................................................................................................ 3
9
Test Methods.................................................................................................................................................. 3
Figures
Figure 1 —Standard Dumb Bell Test Piece.............................................................................................................. 4
Figure 2 —Small Dumb Bell Test Piece.................................................................................................................... 5
Figure 3 — Test Piece For Tear Test ........................................................................................................................ 6
Tables
Table 1 Test Fluids, Temperatures and Limits ........................................................................................................ 8
ii
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DEF STAN 61-12 Part 31 Issue 2
AMENDMENT RECORD
Amd No
Date
Text Affected
Signature and Date
REVISION NOTE
This standard is raised to Issue 2 to update its contents to cover materials other than black.
HISTORICAL RECORD
This standard supersedes the following:
Naval Engineering Standard 518/3
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DEF STAN 61-12 Part 31 Issue 2
Foreword
a) This standard provides requirements for Fire Hazard Sheathing material for Ministry of Defence
(MOD) use.
b) This standard has been produced on behalf of the Defence Material Standardization Committee
DMSC) by The Defence Cables and Interconnections Standardization Committee.
c) This standard has been agreed by the authorities concerned with its use and is intended to be used
whenever relevant in all future designs, contracts, orders etc. and whenever practicable by
amendment to those already in existence. If any difficulty arises which prevents application of the
Defence Standard, UK Defence Standardization (DStan) shall be informed so that a remedy may be
sought.
d) Any enquiries regarding this standard in relation to an invitation to tender or a contract in which it is
incorporated are to be addressed to the responsible technical or supervising authority named in the
invitation to tender or contract.
e) Compliance with this Defence Standard shall not in itself relieve any person from any legal
obligations imposed upon them.
f)
iv
This standard has been devised solely for the use of the Ministry of Defence (MOD) and its
contractors in the execution of contracts for the MOD. To the extent permitted by law, the MOD
hereby excludes all liability whatsoever and howsoever arising (including, but without limitation,
liability resulting from negligence) for any loss or damage however caused when the standard is
used for any other purpose.
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DEF STAN 61-12 Part 31 Issue 2
Introduction
This standard specifies the requirements for limited fire hazard sheathing for electrical cables.
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v
DEF STAN 61-12 Part 31 Issue 2
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vi
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DEF STAN 61-12 Part 31 Issue 2
Wires, Cords and Cables, Electrical, Metric Units Part 31:
Sheaths - Limited Fire Hazard - Standards for Defence
1
Scope
1.1 This Defence Standard specifies the requirements and tests for limited fire hazard
sheathing material for electric cables.
1.2 Cable sheaths manufactured to this chapter present products having limited fire hazard
characteristics when assessed by the methods of test specified herein.
1.3 Cable sheaths manufactured to this chapter shall be suitable for use within the
temperature range -30°C to +105°C. The upper temperature limit refers to the combination of
ambient temperature and the temperature rise due to the continuous current flow in the cable
conductors. The sheathing material shall have a life exceeding 40,000 hours at 85°C
continuous sheath temperature.
2
Warning
The Ministry of Defence (MOD), like its contractors, is subject to both United Kingdom and European
laws regarding Health and Safety at Work, without exemption. All Defence Standards either directly or
indirectly invoke the use of processes and procedures that could be injurious to health if adequate
precautions are not taken. Defence Standards or their use in no way absolves users from complying
with statutory and legal requirements relating to Health and Safety at Work.
3
Related Documents
3.1 The publications shown below are referred to in the text of this standard. Publications
are grouped and listed in alpha numeric order.
Designation
BS 903
Title
Determination of Temperature Rise and Resistance to Fatigue in
Flexometer Testing (Basic Principles)
BS 2782
Method of Testing Plastics Part 1 - Methods 141A to 141D
BS 4727 Part 2 Group 08 Electrotechnical, Power, Telecommunication, Electronics, Lighting and
Colour Terms. Part 2 - Terms Particular to Power Engineering. Group 08
Electric Cable Terminology
BS EN 60216-1
Determination of Thermal Endurance Properties of Electrical Insulating
Materials. Part 1 - General Procedures for Determination of Thermal
Endurance Properties, Temperature Indices and Thermal Endurance
Profiles
BS 6469-98
Methods of Test for Insulation and Sheaths of Electric Cables
Def Stan 91-4/Issue 5
Fuel, Naval Distillate: Low Pour Point
Def Stan 91-110/Issue 1 Lubricating Oil, Gas Turbine Engine Synthetic OX28
DERD 2499
Def Stan 02-711
Determination of the Smoke Index of the Products of Combustion from
Small Specimens of Materials
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DEF STAN 61-12 Part 31 Issue 2
ISO 4589 – 2
ISO 4589 – 3 Annex A
Def Stan 02/713
Determination of burning behaviour by oxygen index- Part 2 Ambient
Temperature Test
Determination of burning behaviour by oxygen index- Part 2 Elevated
Temperature Test– temperature index
Determination of the Toxicity Index of the Products of Combustion from
Small Specimens of Materials
3.2 Reference in this Standard to any related document means in any Invitation to Tender
or contract the edition and all amendments current at the date of such tender or contract
unless a specific edition is indicated.
3.3 In consideration of clause 3.2 above, users shall be fully aware of the issue and
amendment status of all related documents, particularly when forming part of an Invitation to
Tender or contract. Responsibility for the correct application of standards rests with users.
3.4 DStan can advise regarding where related documents are obtained from. Requests for
such information can be made to the DStan Helpdesk. How to contact the helpdesk is
shown on the outside rear cover of Def Stans.
4
Definitions
4.1 For the purpose of this Standard the definitions of terms in BS 4727 Part 2 Group 08
shall apply.
4.2 Primary stage. For the purpose of this Standard the primary stage shall be taken as
being the 'buying in' of the basic materials required, to manufacture the completed cables.
5
Abbreviations
Designation
BS
Def Stan
DMSC
DStan
Fig
MOD
2
Title
British Standard
Defence Standard
Defence Materiel Standardization Committee
UK Defence Standardization
Figure
Ministry of Defence
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DEF STAN 61-12 Part 31 Issue 2
6
General Requirements for Sheathing Materials
6.1 Colour. Unless otherwise specified in the finished cable specification or contract the
sheathing material colour shall be black.
6.2 Cable sheaths to this Defence Standard are to be suitable for use within the
temperature range -30°C to +105°C. The upper temperature limit refers to the combination of
ambient temperature and the temperature rise due to the continuous current flow in the cable
conductors. The sheathing material is to have a life exceeding 40,000 hours at 85°C
continuous sheath temperature.
6.3 Cable sheaths shall withstand flexing and bending at the minimum temperature of
- 30°C.
6.4 The sheaths shall withstand fuel, lubricating oils, hydraulic fluids and water as tested in
accordance with this Standard.
6.5 The sheaths shall withstand normal installation hazards. Cables sheathed with
materials, which meet the requirements of this standard are to be compatible with glands and
suitable for standard supporting, banding and clipping techniques.
6.6 It is required that all types of insulation and sheathing to this Standard shall be mutually
compatible and also be compatible with other types of insulation and sheathing in general
use. This can be verified by completing selected Compatibility (Ageing) Tests.
6.7 Separate demonstrations will be required for compounds, where different, for each of
the different processing techniques, i.e. continuous vulcanization, pan curing and radiation
cross linking.
7
List of tests and sample sizes
7.1 The manufacturer shall have as a minimum carry out tests on representative samples
of sheathing material for which conformance to this standard is claimed. Evidence of such
tests shall be supplied to the purchaser.
7.2
8
All specimens shall satisfy the requirements of this Standard
Test Requirements
8.1 Test samples. All tests, except Insulation Resistance Constant shall be carried out on
samples taken from sheath of completed cable. For demonstration purposes the sample
thickness shall be between 1.45 and 1.55 mm, which must be taken from a 12.5 mm OD or
larger cable.
9
Test Methods
9.1 Tensile strength at break and elongation at break. Dumb bells and tubular samples
from completed cable are to be tested in accordance with the method detailed below:
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DEF STAN 61-12 Part 31 Issue 2
9.1.1 Preparation of test pieces. Prepare 5 standard dumb-bell test pieces, Figure 1, or if the
cable is below 5 mm overall diameter small dumb-bell test pieces, Figure 2, from the cable sheath.
The dumb-bell test pieces are to be taken along the direction of the cable axis. If the sheathing is
greater than 2.0 mm thick or has ridges on the inside caused by the cores, the sheathing is to be
prepared by grinding or cutting (cutting is the preferred method) so as to provide an even thickness
between 0.6 mm to 2.0 mm. If the cable is of such a small size that it is not possible to prepare dumbbell test pieces, prepare 5 tubular test pieces in accordance with BS 6469.
9.1.2 Dumb-bells. Measure the thickness at the centre and at each end of the test length with the
thickness gauge. The mean value of the three measurements shall be used in calculating the area of
the cross section. In any one dumb-bell the thickness of the narrow portion shall nowhere differ by
more than 2% from the mean thickness. If two groups of test pieces are being compared, the mean
thickness of each group shall be within 7.5% of the mean thickness of the two groups. The width of the
test piece shall be taken as the distance between the cutting edges of the die in the narrow part, and
this distance shall be measured in accordance with BS 903 to the nearest 0.05 mm. The measuring
apparatus shall be a micrometer or similar instrument (calibrated in millimetres to 2 decimal places),
having a contact pressure not exceeding 0.07 N/mm2.
9.1.3
Tubular test pieces. Calculate the cross sectional area by the method detailed in BS 6469.
9.1.4 Tensile test procedure. Carry out the tensile test on the test pieces at a temperature of 20 +
5°C/-2°C. Before the start of the test, keep the test pieces for at least 3 hours at the test temperature.
The nominal gauge length is to 20mm for standard dumb-bells and tubular test pieces or 10mm for
small dumb-bells. The rate of separation of the jaws is to be 50mm/min.
9.1.5 Measurements. Measure the load at break and the elongation by measuring the distance of
the gauge length at break, on each test piece. Ignore the measured values if the test piece breaks
outside the gauge length. If less than 5 valid results have been obtained repeat the test
Figure 1 —Standard Dumb Bell Test Piece
4
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DEF STAN 61-12 Part 31 Issue 2
Figure 2 —Small Dumb Bell Test Piece
9.1.6
Evaluation of results
a)
Calculate the tensile strength at break (N/mm2) by dividing the load at break by the cross
sectional area of the unstretched test piece.
b)
Calculate the elongation at break as the increase in distance of the gauge length at break from
the distance between the gauge length of the unstretched test piece as a percentage of the latter.
c)
Classify the results in order of increasing value and take the average of the 3 middle values of the
results for each property.
9.1.7 The tensile strength at break shall be 8 N/mm2 minimum and elongation at break shall be
200% minimum.
NOTE
In addition if a material has a yield, the elongation at yield is to be greater than 120%.
9.2 Tear resistance. Samples are to be tested as detailed below. The sample must be
taken such that the ‘cut’ is longitudinal, in the direction of extrusion.
9.2.1 Preparation of test pieces. Prepare 5 test pieces having dimensions as shown in Figure 3.
Cut these along the direction of the cable axis by means of a die from portions of the sheath from
which all irregularities or corrugations, if present, have been removed by grinding or cutting. Make a
central longitudinal cut, perpendicular to the width of the test piece to a point 3.8 mm from the wider
end. The thickness of each test piece is not to be greater than 2.0 mm and not less than 0.6 mm.
Measure the thickness in mm to the second decimal place at the wider end of the test piece, with a
micrometer or similar instrument with a contact pressure not exceeding 0.07 N/mm2.
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DEF STAN 61-12 Part 31 Issue 2
Figure 3 — Test Piece For Tear Test
9.2.2 Conditioning of test pieces. Before the start of the test keep test pieces for at least 3 hours
at an ambient temperature equal to that at which the test is to be carried out.
9.2.3 Test temperature. Carry out the test at a temperature of 20 + 5°C - 2°C and commence
testing within 5 minutes of removal from the conditioning chamber.
9.2.4 Procedure. Test each test piece as follows: Place the halves of the split end in the jaws of a
tensile testing machine and separate the jaws at a rate of 500 ± 50mm/min.
9.2.5 Evaluation of results. Determine the tear resistance by dividing the maximum load in
Newtons required to tear the section, by the thickness of the test piece in millimetres. Classify the
results in order of increasing value and take the average of the 3 middle values as the tear resistance.
9.2.6
The tear resistance value shall be 5 N/mm minimum.
9.3 Thermal endurance. The thermal endurance profile of the sheathing material is to be
determined as in BS EN 60216-1. The end points to be used are to be 50% ultimate elongation of the
sheathing material after continuous ageing as in BS EN 60216-1.
9.3.1 The Arrhenius plots so obtained are to form part of the submission to MOD when seeking
Approval for the sheathing material. It will be required to show that the sheathing material has a life
exceeding 40,000 hours at a continuous temperature of 85°C.
9.4 Accelerated ageing. The accelerated ageing test is to be carried out on appropriate samples
in accordance with the Thermal Ageing Method of BS EN 60811/1/2 (Ageing in Air Oven). The
samples shall be aged for 7, 14 and 28 days at 110 ± 2°C. The properties of tensile strength,
elongation at break and tear resistance shall be measured after each ageing period. The difference in
the values of the above properties at the end of the 14 day period and the end of the 28 day period
shall not exceed 20%. The elongation at break after the 28day ageing period shall be equal to or
greater than 150%.
Critical oxygen index. Samples shall be tested to the requirements of BS 2782 Part 1,
Method 141, the thickness shall be between 1.45 mm and 1.55 mm, and the ignition time (see clause
8.2 of ISO 4589-2 shall be 15 seconds.
9.5
9.5.1
The value of the critical oxygen index shall be 29 minimum.
9.6 Temperature index. Samples shall be tested to the requirements of ISO 4589 – 3 Annex A,
except that the test specimen is to be a 70 mm to 150 mm length.
9.6.1
6
The value of the temperature index shall be 250°C minimum.
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DEF STAN 61-12 Part 31 Issue 2
9.7
Toxicity index. Samples shall be tested to the requirements of Def Stan 61-12 (part 0)
clause16.19.
9.7.1 The toxicity index shall be expressed in terms of 100 g of material and the value shall be 5
maximum.
Halogen content. The sheathing material is to be testing for potential acid gas evolution by
using the Lassaigne Test (sodium fusion test). A 0.25 g ± 100 mg sample, approximately 25 mm
length, of sheathing material, stripped from the test sample, and cut into small pieces, shall be
subjected to the above test, for fluorine, chlorine, bromine and iodine.
9.8
NOTE
9.8.1
This test can be dangerous if carried out by inexperienced operators.
A negative result shall be obtained i.e. no detectable halogens.
Smoke Index. Samples shall be tested to the requirements of Def Stan 61-12 (Part 0) clause
13.42. The value of the smoke index shall be 20 maximum.
9.9
9.10 Resistance to fluids. Samples are to be tested in accordance with Def Stan 61-12 (Part 0)
clause 16.14 using the fluids listed in Table 1 of this Defence Standard
NOTE
Compliance with this test provides no guarantee that the sheath is suitable for continuous use in the
listed fluids.
9.10.1 Dumb-bell test pieces in accordance with Figure 1, 75 mm long are to be immersed for 28
days in each of the fluids in Table 1 (of this Defence Standard), at the temperatures stated. At the end
of the immersion period the samples are to be removed from the fluid and subjected to volume swell,
tensile strength and elongation at break tests. The requirements are detailed in Table 1 of this
Defence Standard.
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DEF STAN 61-12 Part 31 Issue 2
Table 1 Test Fluids, Temperatures and Limits
TEST
TEMP
FLUID
(a)
FUEL OIL
TENSILE
STRENTH
% UNTREATED
SAMPLE
ELONGATION
AT BREAK
% UNTREATED
SAMPLE
(c)
(d)
(b)
VOLUME
SWELL
%
(e)
20 ± 3°C
60 min
60 min
25 max
50 ± 3°C
60 min
60 min
15 max
Water/Glycol based OX 40 Def
Stan 91-110
50 ± 3°C
60 min
60 min
15 max
LUBRICATING OIL
50 ± 3°C
60 min
60 min
10 max
Synthetic ester base OX-28
(DERD 2499)
50 ± 3°C
60 min
60 min
50 max
WATER
50 ± 3°C
80 min
80 min
10 max
50 ± 3°C
80 min
80 min
10 max
Dieso 47/20, NATO F-76 DEF
STAN 91-4/Issue 5(or DERV)
HYDRAULIC FLUID
Petroleum based OX 30 Def
Stan 91-35
Detergent Mineral OMD-113
Deionized
Deionized with 3½% NaCl
9.11 Cold elongation. Samples shall be tested in accordance with BS 6469 - Tests at low
temperature, elongation test at low temperature for sheaths, except that the test temperature is to be
within the limits -30°C to -34°C.
9.11.1 The cold elongation shall be 20% minimum.
9.12 Heat shock. Samples of cable sheath shall be tested to the requirements of BS 6469 Section
4.4.3, except that the temperature of 150°C ± 3°C is to be maintained for 4 hours.
9.12.1 On completion of the test no cracks shall be apparent in the sheathing, when using normal or
corrected vision.
9.13 Insulation resistance constant. This test shall be carried out as detailed below on a
sample of collectively screened cable at least 5m in length, which has no tape over the screen:
8
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DEF STAN 61-12 Part 31 Issue 2
9.13.1 Immerse the sample in water for 28 days at 20°C +5°C -2°C with a length of 250 mm at each
end of the cable protruding above the water.
9.13.2 Apply a direct current voltage of 500 V ±10% between the screen and the water, on
completion of immersion period.
9.13.3 Measure the insulation resistance 1 minute after application of the voltage.
9.13.4 Calculate the insulation resistance constant (K) from the equation:
K=
LR MΩ km
1000 log10
(D)
(d)
where D is diameter over sheath (mm)
d is diameter over screen (mm)
L is immersed length of cable (m)
R is insulation resistance of length of cable (MΩ)
9.13.5 The value of the insulation resistance constant shall be 0.1MΩ km minimum.
9.14 Hot set test. To confirm that the sheath has been adequately cross linked, the hot set test of
BS 6469 Section 3.3 shall be performed. The test temperature shall be 200 ± 5°C and the stress on
the sample shall be 0.2 N/mm2.
9.14.1 The maximum elongation shall be 175% and the maximum permanent elongation shall be not
greater than 25%.
9.15 Pressure test. Samples shall be tested in accordance with BS 6469 Section 4.2.3. The
temperature shall be 120°C ± 3°C.
9.15.1 The indentation shall not exceed 50%.
9.16 Ozone resistance test. Samples shall be subjected to the test specified in BS 6469 Section
3.2. The ozone concentration shall be 80 to 100 ppm for a duration of 120 ± 2 hours.
9.16.1 On completion of the test no cracks shall be apparent in the sheathing, when using normal or
corrected vision.
9.17 Resistance to Ultra Violet. Samples of each colour of material shall be subjected to the test
in Defence Standard 61-12 (Part 0) clause 16.16.
a)
Test Cycle periods:
UV
:
8 hours
Humidity
:
4 hours
b)
Ultra Violet lamp type
:
UV-B/A
c)
Test period
:
1000 hours
d)
Test Temperatures
:
UV period
:
55±3oC
Humidity period
:
40±3oC
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DEF STAN 61-12 Part 31 Issue 2
9.17.1 On completion the minimum tensile strength shall be not less than 50 % and the elongation at
break 50% of the original unexposed material.
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File Reference
The DStan file reference relating to work on this standard is D/Dstan/61/12/31.
Contract Requirements
When Defence Standards are incorporated into contracts users are responsible for their correct
application and for complying with contractual and statutory requirements. Compliance with a
Defence Standard does not in itself confer immunity from legal obligations.
Revision of Defence Standards
Defence Standards are revised as necessary by an up issue or amendment. It is important that
users of Defence Standards should ascertain that they are in possession of the latest issue or
amendment. Information on all Defence Standards is contained in Def Stan 00-00 Standards for
Defence Part 3 Index of Standards for Defence Procurement Section 4 'Index of Defence
Standards and Defence Specifications' published annually and supplemented regularly by
Standards in Defence News (SID News). Any person who, when making use of a Defence
Standard encounters an inaccuracy or ambiguity is requested to notify UK Defence
Standardization (DStan) without delay on order that the matter may be investigated and
appropriate action taken.