2391 Question !!

[newfoundspark]

Doing the 2391 soon, and have a question about the test !

There is a submain board, which is fed by a 100A 30ma RCD (i believe), and understand that, i will do a Zs on this - as it is a circuit fed by the 3 phase board.

I will then make sure the main switch, in this case the 100A 30mA RCD is turned off, remove the earthing conductor, connect one lead to this, and then the other to the incoming side of the main's live terminal, in order to perform the test for Ze ?

How would i perform the RCD test on this, would i connect one lead to the Earth Terminal, and then the other 2 leads to the outgoing side of the RCD, how will i connect to the live ???

Could someone try to help clear this up please ! Thanks

 

[Chri5]

RCD's are tested live, so at any point at or beyond the RCD, at an MCB, circuit end. socket, ceiling rose etc it should trip with the tester set according to the RCD test rate.

I still test each circuit on an RCD, although recently I've seen EIC's that test the RCD for each group of circuits on that RCD rather than at each circuit.
My logic being that is right to record a result for each circuit on the RCD.

 

[Spark123]

Once you have reconnected the main earth and done the rest of the tests you can finally do the RCD as a functional test.
Most testers only require 2 leads (phase and earth) to do RCD however if yours doesn't you need to connect the red lead to outgoing phase, black to outgoing neutral and clip the green to earth, do the RCD test as per normal just using one of the phases.

 

[securespark]

Ask a manufacturer the correct way to test an RCD and they will say in isolation.

I don't feel the need to check that the RCD works from all given points in a circuit - provided they are wired as they should be, there will not be a problem.

 

[oharaf]

From what you describe this sounds correct.

I also used to test the RCD on each circuit, but I now resorted to testing the circuit with the highest R1+R2 reading for each group of circuits

 

[riveralt]

I did my 2391 last June (and passed). The set up on my board was slightly different in that the sub main was fed from the three phase distribution board via a 60amp mcb. The RCD was part of a socket on one of the submain circuits. So testing the RCD both mechanically and electrically was relatively easy, especially if you have the right test equipment. A different set up but the principle is the same.

Don't forget that you must test for Zs on the submain circuit before testing the RCD (411.4.5) or its a fail. I asked if I could just use the Ze + (R1 +R2) - nope!

Also GN3 implies that the purpose of the RCD test is to test the RCD not the circuit (as securespark rightly states). So test the easiest circuit and ensure that you or your test machine does the six RCD tests. Remember that time is always ticking on this test.

I'm not sure why you are thinking of connecting the leads as you say. Most modern testers and certainly those at any test centre should have a specific plug adapter that fits into your tester. You use it to plug into any socket on the circuit to test for Zs and the RCD

Good luck in your exam