Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, concerning radial sockets supplied from power busbars, and what testing is needed, is answered by SELECT:
Answer: Radial sockets should not be supplied direct from power busbars - they should be supplied from an appropriate protective device. Then appropriate testing can be carried out, such as continuity (either R2 or (R1 + R2), insulation resistance and earth loop impedance etc.
It may be permissible to supply, say, a spur point (for example for the likes of main F/A switch) from the busbars, generally providing that the tails are no more than 3m in length. Testing of the tails would then entail isolation of the busbars prior to carrying out the appropriate testing.
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