Ministry of Defence Defence Standard (Part 31) Wires, Cords and Cables, Electrical Metric Units Part 31: Sheaths - Limited Fire Hazard,

Transcription

1 Ministry of Defence Defence Standard (Part 31) Issue 2 Publication Date 20 th January 2006 Wires, Cords and Cables, Electrical Metric Units Part 31: Sheaths - Limited Fire Hazard,

2 Contents Introduction...v 1 Scope Warning Related Documents Definitions Abbreviations General Requirements for Sheathing Materials List of tests and sample sizes Test Requirements 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

3 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 iii

4 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) 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. iv

5 Introduction This standard specifies the requirements for limited fire hazard sheathing for electrical cables. v

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7 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 Title BS 903 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 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 Methods of Test for Insulation and Sheaths of Electric Cables Def Stan 91-4/Issue 5 Fuel, Naval Distillate: Low Pour Point Def Stan /Issue 1 DERD 2499 Def Stan Lubricating Oil, Gas Turbine Engine Synthetic OX28 Determination of the Smoke Index of the Products of Combustion from Small Specimens of Materials 1

8 ISO ISO 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 Title British Standard Defence Standard Defence Materiel Standardization Committee UK Defence Standardization Figure Ministry of Defence 2

9 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 All specimens shall satisfy the requirements of this Standard 8 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: 3

10 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 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/mm Tubular test pieces. Calculate the cross sectional area by the method detailed in BS Tensile test procedure. Carry out the tensile test on the test pieces at a temperature of 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 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

11 Figure 2 Small Dumb Bell Test Piece Evaluation of results a) Calculate the tensile strength at break (N/mm 2 ) 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 The tensile strength at break shall be 8 N/mm 2 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 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/mm 2. 5

12 Figure 3 Test Piece For Tear Test 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 Test temperature. Carry out the test at a temperature of C - 2 C and commence testing within 5 minutes of removal from the conditioning chamber 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 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 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 The end points to be used are to be 50% ultimate elongation of the sheathing material after continuous ageing as in BS EN 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%. 9.5 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 shall be 15 seconds The value of the critical oxygen index shall be 29 minimum. 9.6 Temperature index. Samples shall be tested to the requirements of ISO Annex A, except that the test specimen is to be a 70 mm to 150 mm length The value of the temperature index shall be 250 C minimum. 6

13 9.7 Toxicity index. Samples shall be tested to the requirements of Def Stan (part 0) clause The toxicity index shall be expressed in terms of 100 g of material and the value shall be 5 maximum. 9.8 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. NOTE This test can be dangerous if carried out by inexperienced operators A negative result shall be obtained i.e. no detectable halogens. 9.9 Smoke Index. Samples shall be tested to the requirements of Def Stan (Part 0) clause The value of the smoke index shall be 20 maximum Resistance to fluids. Samples are to be tested in accordance with Def Stan (Part 0) clause 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 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. 7

14 Table 1 Test Fluids, Temperatures and Limits FLUID TEST TEMP TENSILE STRENTH % UNTREATED SAMPLE ELONGATION AT BREAK % UNTREATED SAMPLE VOLUME SWELL % (a) (b) (c) (d) (e) FUEL OIL 20 ± 3 C 60 min 60 min 25 max Dieso 47/20, NATO F-76 DEF STAN 91-4/Issue 5(or DERV) HYDRAULIC FLUID 50 ± 3 C 60 min 60 min 15 max Petroleum based OX 30 Def Stan Water/Glycol based OX 40 Def Stan LUBRICATING OIL 50 ± 3 C 60 min 60 min 15 max 50 ± 3 C 60 min 60 min 10 max Detergent Mineral OMD-113 Synthetic ester base OX-28 (DERD 2499) WATER 50 ± 3 C 60 min 60 min 50 max 50 ± 3 C 80 min 80 min 10 max Deionized Deionized with 3½% NaCl 50 ± 3 C 80 min 80 min 10 max 9.11 Cold elongation. Samples shall be tested in accordance with BS 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 The cold elongation shall be 20% minimum 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 On completion of the test no cracks shall be apparent in the sheathing, when using normal or corrected vision 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

15 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 Apply a direct current voltage of 500 V ±10% between the screen and the water, on completion of immersion period Measure the insulation resistance 1 minute after application of the voltage Calculate the insulation resistance constant (K) from the equation: K = LR MΩ km 1000 log 10 (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) The value of the insulation resistance constant shall be 0.1MΩ km minimum 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/mm The maximum elongation shall be 175% and the maximum permanent elongation shall be not greater than 25% Pressure test. Samples shall be tested in accordance with BS 6469 Section The temperature shall be 120 C ± 3 C The indentation shall not exceed 50% 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 On completion of the test no cracks shall be apparent in the sheathing, when using normal or corrected vision Resistance to Ultra Violet. Samples of each colour of material shall be subjected to the test in Defence Standard (Part 0) clause 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±3 o C Humidity period : 40±3 o C 9

16 On completion the minimum tensile strength shall be not less than 50 % and the elongation at break 50% of the original unexposed material. 10

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18 Crown Copyright 2006 Copying Only as Agreed with DStan Defence Standards are Published by and Obtainable from: Defence Procurement Agency An Executive Agency of The Ministry of Defence UK Defence Standardization Kentigern House 65 Brown Street GLASGOW G2 8EX DStan Helpdesk Tel /2 Fax Internet 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 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.