BS 3475-604:2010 pdf download – Cables, electrical, aircraft use — Test methods — Part 604: Resistance to dry arc propagation
5.2 Test equipment Construct an apparatus as shown diagrammatically in figures 3a, 3b and 3c which includes the following minimum provisions:
a) A lightweight, freely pivoting test fixture to hold the blade at a 90° angle to the specimen and to exert a controlled force on the specimen. NOTE Generally a mounting on 50 mm centres shall hold the individual cables of the specimen in close proximity.
b) Electrical terminations to provide a ready means of connecting test specimens into the circuit as shown in figure 2.
c) An aluminium blade complying with material specification T6061 -T6 (EN 2702) and figure 3c.
d) A mechanism to provide a minimum oscillating stroke of 1 5 mm excursion at a frequency of (8 ± 2 ) Hz.
e) A blade carrier to give a downward force at the blade of (2,5 ± 0,1 ) N.
f) A mechanical stop to limit the fall of the oscillating blade to within an accuracy of 0,2 mm measured at the point of contact.
g) Means of separating the blade from the specimen, both manually and automatically if used.
h) An electrical connection of the aluminium blade to the neutral of the test power supply (see 5.1 h).
i) A transparent enclosure to protect personnel from ejected molten metal and short wavelength ultra violet light.
5.3 Test protocol
5.3.1 The procedure embraces cables sizes 26 to 1 0, and for each cable size six values of prospective fault current have been defined. Performance of a cable size at a given fault intensity shall be determined by testing three samples. Thus 1 8 samples are required for every cable size.
5.3.2 For the purposes of cable qualification at least sizes 24, 20 and 1 4 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 and the blade form to be employed 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 i). 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 size to be tested (table 2). Fit a blade to the reciprocating head of the test rig of the appropriate type shown in figures 3a) and 3b).
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 With electrical power removed adjust the test apparatus to give the correct conditions of blade stroke, frequency and downwards force. Ensure that the test fixture is correctly positioned and that the method of holding the specimen provides satisfactory restraint. 5.4.4 Modify a verification sample by removing a section of cables A1 and B1 in the test zone. Adjust the blade depth stop such that the blade just contacts the insulation of cables A2, B2 and C1 .
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 .
6.1.2 Apply electrical power to the specimen and gently make contact with the blade. Arm the automatic blade lifting circuit, if used, and start the abrading action. NOTE 1 Only blades in good condition shall be used on new samples. If the abrading edge of a blade becomes significantly degraded after a circuit breaker trip at any stage it shall be replaced. NOTE 2 Before each test series check that thermal breakers are operating within their specified trip limits when subjected to 1 00 % overload. NOTE 3 Shall it be established that the mechanical attack of the blade does not penetrate the insulation within 3 min, then it is permissible for a fine cut to be made on the test specimens at the point on the upper surface of cables A1 and B1 where the blade is to make contact. No material shall be removed and the cut shall not penetrate to the conductor.