Tripping RCD

[lofty84]

One of the RCDs keeps tripping in one of the propertys we are working on. The RCD supports the ring in the kitchen, lights and doorbell from what I can remember. when we put the ring on the other rcd in the consumer unit it didnt trip, but we need to investigate this tommorow. Any ideas whats happening. I know the purpose of a rcd is to monitor the circuits it is protecting and turn its self of if it notices a difference in current going out on the line and back on the neautral of 30mA or more.

 

[topquark]

One rather assumes that continuity, insulation resistance and polarity have already been done and sucessful as they are DEAD tests and we're already on to live testing

 

[Deleted member 9648]

One rather assumes that continuity, insulation resistance and polarity have already been done and sucessful as they are DEAD tests and we're already on to live testing

One suspects not mate.

 

[topquark]

Hi Lofty84, can you please summarise for us what testing you have done so far

 

[telectrix]

flash/bang?

 

[topquark]

The thought process was that dead tests were complete and as we all know the IR tests check the final circuits only, they don't check out the CU wiring itself (but do affect the RCD/RCBO behaviour) hence suggesting the main neutrals in the CU be checked.

 

[Nolnoc]

The first thread said doorbell is on the rcd. Maybe I'm reading it wrong but is the rcd feeding a transformer. If so then some transformers are notorious for tripping rcds.Its only a stab at the dark but I would start there.

 

[lofty84]

we changed the rcd for a new one and it was still tripping if that helps

 

[topquark]

The mere presence of a transformer shouldn't have any effect unless it's drawing a load.

 

[telectrix]

my 110v site tranny takes out a 16A type B without being loaded.

 

[lofty84]

im ashamed to say no no dead tests have been done its a case of get it in and move on to the next one. someone is supposed to come out and test but they havent yet. Im picking the tester up tommorow so will be performing the dead tests

 

[Nolnoc]

mine too
Maybe rcd only trips when someone rings doorbell lol

 

[topquark]

my 110v site tranny takes out a 16A type B without being loaded.

That I can understand as it'll be center tapped and will be constant voltage (ie active not passive), maybe the doorbell transformers are too ?

 

[topquark]

mine too
Maybe rcd only trips when someone rings doorbell lol

Only if it's Avon calling, I need beer

 

[lofty84]

Ive got the onsite guide to refer to tommorow and read in a minute, but i dont suppose someone wants to talk me through the tests just to refresh things idealy from start ton finish of exactly how u go about it.

 

[topquark]

Of the top of me bonce, assuming a newly installed circuit.

Visual checks (usually done during construction if working alone).
End to end continuity of conductors, using either R1+R2 method or wandering lead method (favour the first as you'll get polarity as a side effect).
Insulation resistance testing of conductors for final circuits
Polarity checks.

Then on to live testing:
Live Polarity Test.
Ze, current tests, Zs.
Then on to RCD/RCBO tests
and finally functional testing.

In practice for an existing installation you'd normally check Ze, PSSC etc before hand