Cables operating at or above 1 kV a.c. should be subjected to a high voltage dielectric test after terminations have been completed. These tests should be made prior to connection to the apparatus unless links are provided to allow isolation of the cable from the apparatus. The test voltage should be d.c. at 4 times the rated voltage for a duration of 15 minutes.
Where it is not possible to separate the cable(s) from the equipment for the test, a test voltage and duration, appropriate to the type of equipment to which the cables are connected, should be applied.
High voltages tests can weaken the dielectric materials and should, therefore, only be carried out at the time of initial installation. Any subsequent tests following additions, modifications or repairs should be applied with caution and then only at reduced voltages as recommended by the relevant British Standard.
The above tests should always be preceded and followed by an insulation resistance test.
4 Earth continuity
(1) Tests should be made to verify that all earth continuity conductors and earthing leads are connected to the frame of apparatus and to the hull of metal ships or the main earth conductor bar of ships with non-metallic hulls and that socket-outlet earthing terminals are connected to earth. This should also apply where apparatus is bonded directly to the hull.
The earthing arrangements of some control, instrumentation and/or intrinsically safe systems may differ from the normal power earth arrangements and should be given special consideration, e.g. low voltage/low current test equipment.
(2) Where metal-sheathed cables are used, whether armoured or not, tests should be made to verify that all metallic envelopes are electrically continuous throughout their length and are earthed as required, or as may be required for particular arrangements such as when they form part of a control, instrument or intrinsically safe system.
(3) Where earthed systems are used, it should be verified that：
(i) Single-pole control devices and fuses are connected in the live conductor only. (It should be noted that double-pole isolation is required for installations in hazardous areas.)
(ii) Wiring has been connected correctly to plugs and sockets.
(iii) The outer contacts of Edison screw-type lampholders are connected to the earthed conductor.
5 Earth fault loop impedance
Where protective measures are used which require a knowledge of earth fault loop impedance, the relevant impedances should be measured, or determined by an equally effective method.
Tests should be made at the completion and be re-assessed at periodic intervals, but care should be taken on installations in hazardous areas, as mentioned in 6.
6 Tests on installations in hazardous areas
(1) Where tests involve equipment that is situated in or circuits that pass through a hazardous area, care should be taken that the tests required by 2 to 5 do not cause incendive arcs, sparks or hot surfaces.
(2) The testing of the installation prior to the introduction of the potentially hazardous materials may be carried out using normal methods but subsequent testing may require alternative techniques. (Refer to relevant IEC Standard).
(3) Care should also be exercised with the use of intrinsically safe test instruments as, under certain conditions, they could result in the production of incendive sparks.
(4) Care should be taken when testing to ensure that intrinsically safe systems and their earthing arrangements are not violated.
7 Performance Tests
(1) All switchgear should be loaded as nearly as practicable to its working load in order to demonstrate that no overheating takes place due to faulty connections or incorrect rating.
