Rcd do not trip at x1

Joe100w · Posted: Mon Apr 06, 2009 2:22 pm Post Subject: Rcd do not trip at x1

hi,

I am testing a circuit that goes to the garden with armoured cable. The RCD will not trip at x 1 (gets over 400ms) but trips fine on x5. The other circuits seems to be fine with the RCD test (30 mA). Using megger mft 1552. Any reason?

When I move that circuit to the other RCD (30 mA) it trips fine within the time.

My puzzle why will the garden circuit not trip at x 1. What could have been wrong.

Thanks.

ColJack · Posted: Mon Apr 06, 2009 2:31 pm Post Subject:

distance of run? dodgy earth? dodgy neutral?

what are the Zs readings for the garden circuit?

securespark · Posted: Mon Apr 06, 2009 4:06 pm Post Subject:

It is incorrect to test an RCD from a final circuit.

Test it in isolation.

What was the Zs at that point before you started work?

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Joe100w · Posted: Mon Apr 06, 2009 4:27 pm Post Subject:

Zs is 1.32, Protected by type B MCB rated at 16A. Wiring all 3 is 2.5 mm and the armoured also is connected to Earth.

Insulation resistance >299 on all three.

Could not get a trip on 1 RCD with several attemps, but same circuit was fine when swapped over to the other RCD

securespark · Posted: Mon Apr 06, 2009 4:32 pm Post Subject:

Test the RCD in isolation. If it fails, swap it out.

__________________
As George Michael once said, "..if you're gonna do it, do it right, right?"

Joe100w · Posted: Mon Apr 06, 2009 5:15 pm Post Subject:

Securespart

Might sound silly, how do I test Rcd in isolation.

ColJack · Posted: Mon Apr 06, 2009 5:26 pm Post Subject:

take the cables out of it and put the test leads on the load side of it...

securespark · Posted: Mon Apr 06, 2009 10:43 pm Post Subject:

Or if it is difficult to take the cables out of the outgoing terminals, switch off all the MCB's attached to that RCD to isolate the live terminal, then either disconnect all the neutrals from the busbar attached to that RCD or pull out (if it is flexible) the neutral feed to that busbar.

__________________
As George Michael once said, "..if you're gonna do it, do it right, right?"