RCD Testing

26 Apr 2007
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United Kingdom

I’ll soon be installing a new radial circuit to my utility room and need some advice from the experts regarding final testing, please.

The circuit will consist of 6mm T&E in surface trunking from the RCD (30mA 80A) side of my Wylex split-load CU, to feed 4 double sockets in the utility room, then terminating at a fifth double socket (MK Masterseal) on the outside of the house. Total length of the circuit will be about 14 m, and will be protected by a 32A MCB.

On completion I plan to test continuity and insulation resistance, but i'm not sure how to test the RCD. I've come across some RCD testers that measure trip times etc, but they are expensive kit, starting at about £200 I think. Are there any other ways to measure RCD performance?

Cheers for any help.
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RobFurn said:
Just a quick question have your heard of part P ?

Also, good luck trying to terminate 2 x 6mm² cables in each socket!

You need an RCD tester to correctly test an RCD ;)
Do you also have an earth fault loop impedance tester? It is important that the earth fault loop is checked before the RCD is tested.
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If the circuit your planning is only in a utility room and is part of the house(no need to run cables outside) why not run the radials in either ...
A) 2.5mm T&E protected by a 20Amp mcb
B) 4mm T&E protected by a 32Amp mcb
The 14 meter run your planning is fine for volt drop in both these cables.

What are you actually going to run in this utility room?
sussexrich said:
Are there any other ways to measure RCD performance?

Not really.

You need to test the RCD in isolation from any circuitry.
Doesn't look like it does 5 x I/\n which is the important one for testing RCDs which are installed to provide additional protection against electric shock. Also doesn't do + and - cycles which are part of an electricians RCD tester. As far as it goes, it is no where near a replacement for a proper tester.
Can you check the loop impedance, it is important to do this before attempting to conduct tests on an RCD, if your earth is not present and RCD tester may cause exposed parts to become live.
Are you aware of Part P and its requirements?
^just checking! as for an alternative RCD tester i have thought of using my hand-held storage oscilloscope (+appropriate resisters) to test one, although i never have needed to test one.

best bet would be using the proper equipment, there was a thread about hiring a while back, but i never saw the outcome if there was anywhere that rented them out or not.

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