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BS EN 3475-605:2018

BS EN 3475-605:2018

$86.31

Aerospace series. Cables, electrical, aircraft use. Test methods – Wet short circuit test

Published By Publication Date Number of Pages
BSI 2018 14
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This European Standard specifies a method for appraising the behaviour of cable insulation subjected to an electric arc initiated and maintained by a contaminating fluid. This European Standard shall be used together with EN 3475-100. The primary aim of this test is: – to produce, in a controlled fashion, continuous failure effects which are representative of those which may occur in service when a typical cable bundle is damaged and subjected to aqueous fluid contamination such that electrical arcing occurs between cables; – to examine the aptitude of the insulation to track to propagate electric arc to the electrical origin. Originally defined for 115 Vac network, this test also proposes conditions for 230 Vac network. Unless otherwise specified in product standard, only 115 Vac conditions shall be satisfied. Six (6) levels of prospective fault current have been specified for concerned cable sizes (see Clause 7). It is generally agreed that larger sizes need not be assessed since the short-circuit phenomenon becomes dominant at low line impedances. Unless otherwise specified in the technical/product standard sizes 002, 006 and 020 cable shall be assessed.

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PDF Pages PDF Title
2 undefined
6 1 Scope
2 Normative references
3 Specimen requirements
4 Preparation of specimen
4.1 Cut seven (7) separate lengths of approximately 0,5 m consecutively from one (1) length of cable, and strip one of the ends of insulation to permit electrical connection. Clean each length of cable with a clean cloth moistened with propan-2-ol (isopropyl alcohol) fluid.
7 4.2 Lay up the seven (7) cables as follows:
8 5 Apparatus
5.1 Electrical equipment
9 5.2 Test equipment
10 5.3 Test protocol
5.3.1 The procedure embraces copper cable sizes 001 to 051 (26 to 10) or copper clad aluminium cable sizes 002 to 090 (24 to 8), and for each cable size six (6) values of prospective fault current have been defined. Performance of a cable size at a given fault intensity shall be determined by testing three (3) samples. Thus 18 samples are required for every cable size.
5.3.2 For the purposes of cable qualification at least sizes 002, 006 and 020 shall be tested. Additional testing of other sizes may be deemed necessary in particular cases and values of prospective fault currents, the ratings of thermal breaker protection which are typical of aircraft use have been included in this specification.
5.3.3 It is emphasised that electrical arcing tests are essentially destructive and can be hazardous to personnel. Therefore tests shall be undertaken with all observers shielded from direct physical and visual exposure as noted in 5.2 b). The use of video recording for all tests is required.
5.4 Test rig set-up
5.4.1 Install the rating of circuit breaker appropriate to the cable type and size to be tested (Table 3).
5.4.2 Heavy duty electrical shorting connections shall be fitted in substitution of a test sample to enable prospective fault currents to be set by adjustment of resistances Rf. Because these currents would trip the thermal breakers very rapidly these shall be shunted to permit the pulsing of current until the desired value is obtained. Re-instate the thermal protection.
5.4.3 Prepare an electrolyte solution made by dissolving 3 % ± 0,5 % by weight of sodium chloride in distilled water.
5.4.4 Support the specimen in free air inclined at an angle of 10° to the horizontal with the electrical input connections at the higher end.
5.4.5 Position the delivery system so that the electrolyte contacts the loom from a height of (10 ( 2) mm above the uppermost cables in the loom at a point which shall position the droplets into the upper cut or no more than 2 mm towards the higher end of the specimen. Ensure that the drops strike the cables at the top centre of the circumference such that they fall into the crevice between cables A1 and B1.
6 Method
6.1 Test procedure
6.1.1 Install a test specimen with electrical connections as shown in Figure 1 and with Rf set, as in 5.4.2 above, to give the required current from Table 1 or Table 2.
6.1.2 Apply electrical power to the specimen and start the flow of electrolyte at a rate of (100 ( 10) mg/min. Particular care shall be taken to ensure that the electrolyte flows between the damage sites as evidenced by steaming of the electrolyte and the development of scintillation. Shall this not occur, and failure of the cable to wet be determined, then the alternative surfactant described in 5.4.3 may be used.
6.1.3 Run the test continuously for a period of 2 h.
11 6.1.4 Following CB(s) tripping adopt the following procedure:
6.1.5 Repeat the test to obtain three (3) samples and then reset the circuit for the next highest current overload until all 18 samples have been tested.
6.2 Examination
6.3 Test report
7 Requirements

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BS EN 3475-605:2018
$86.31