boiler tripping out rcd

[deadshort]

The boiler maybe providing an earth path for an existing wiring fault on the installation which has nothing to do with the boiler other than providing a better earth than your MET.

Regards,

DS

 

[JohnW2]

It depends upon the extent (impedance) of the fault, doesn't it?

Not if it is a circuit N-E fault and a non-faulty boiler trips it then, surely, a kettle would.

Sure, if an N-E fault somewhere were of sufficiently low impedance that a non-faulty boiler tripped the RCD, then a kettle certainly would as well. However, as I went on to say, I was talking about a 'faulty' boiler (or, at least, one which resulted in a small leak to earth). In that situation, if the circuit fault of was of sufficiently high impedance that a kettle didn't result in a trip, a 'leaky' boiler might be the 'final straw' which resulted in a trip.

You seem to be thinking of a low (maybe even negligible) impedance N-E fault - in which case, as you imply, connecting almost any significant load (not just the boiler) ought to result in a trip. However, if it were a very high impedance N-E fault (only detectable by IR testing), it might never, in itself, be enough to result in an RCD trip, even if large (but 'non-leaky') loads were connected - but the RCD could trip if another load with a small leak ('the last straw') was connected.

Yes, that makes sense and may, indeed, be the solution - but that would also be the case with just accumulated leakage without a circuit fault.

Yes - but, if it's really true that there were absolutely no connected loads (connected to the RCD, not just the final circuit in question), the only place for there to be any leakage to 'accumulate' with that from the boiler would be in the circuit itself, wouldn't it?

Surely "a very high impedance N-E fault" that resulted in a boiler tripping the RCD could not sustain a kettle.

No - as above, if the impedance of the circuit fault was high enough that a (non-leaky) kettle did not result in a trip, it's still possible that a leaky boiler would result in enough accumulated leak (circuit+bolier) to result in a trip, isn't it?

Have we definitely determined that the boiler trips this one circuit with nothing else plugged in to it?

As I'm about to ask the OP again, he has to ensure that nothing protected by the same RCD is 'plugged in'/connected - not just things plugged in to the final circuit in question.

Kind Regards, John

 

[JohnW2]

Have we definitely determined that the boiler trips this one circuit with nothing else plugged in to it?

Yes I have tested the boiler with everything unplugged on this circuit. It trips.

As I said before, you don't have to only unplug/disconnect/isolate everything on the same circuit - you have to do that for anything/everything on circuits that are served by the same RCD - depending upon the arrangement of your CU, that might involving switching off all lights and isolating things like cookers, immersion heaters etc. (and anything plugged into any other sockets circuit served by the same RCD).

Kind Regards, John

 

[huwy123]

To update you all it was solved this morning. The sparky found a wiring fault on a socket (fortunately the first one he looked at). Boiler now plugged in and working.

Thanks for all the advice. Its great having a forum like this to help with these problems.

 

[PrenticeBoyofDerry]

Was this the socket the boiler was plugged into?
or possibly the one that the boiler socket was spurred from?
As it is strange that the fault was not detected unless the boiler was plugged in, unless deadshort's suggestion of a better path to earth being provided by the boiler has some substance.

 

[huwy123]

No it was another socket (upstairs).

Deadshorts suggestion sounds right (in my unqualified opinion!)

 

[PrenticeBoyofDerry]

Deadshorts suggestion sounds right (in my unqualified opinion!)[/quote]

Shsss..Don't tell him that!

 

[JohnW2]

Deadshorts suggestion sounds right (in my unqualified opinion!)

The only thing I wondered about that suggestion is that it requires at least two faults, doesn't it? ... firstly a fault (or, at least, problem in the installation) that means that the boiler provided a better path to earth than did the CPC/MET and, secondly, some fault which resulted in current through the earth path?

Kind Regards, John

 

[EFLImpudence]

I agree.

Doesn't that mean the proper earth path is not good enough or missing?

 

[JohnW2]

I agree. Doesn't that mean the proper earth path is not good enough or missing?

That seemed to be what deadshort was implying - I can't think of any other way in which a boiler would provide a better path to earth than the MET - which is what he said.

A fault in the circuit's CPC could, of course, be that 'first fault' (effectively breaking the connection to the MET. However, in the absence of a second fault, that in itself should not cause an RCD to trip when a decent path to earth was provided by plugging in the boiler. An installation without faults should not behave any differently with and without a proper path from its CPCs to earth.

Kind Regards, John

 

[EFLImpudence]

But electrician found a fault in a socket.

It could have been socket screw contacting neutral with cpc (still?) not earthed but connected to boiler.

 

[JohnW2]

But electrician found a fault in a socket. ... It could have been socket screw contacting neutral with cpc (still?) not earthed but connected to boiler.

Sure - but I'd still count that as 'two faults' - (1) N-CPC fault and (2) CPC not connected to earth (until boiler plugged in). Wouldn't you?

Kind Regards, John

 

[EFLImpudence]

Oh, yes, not questioning that.

However, have they both been rectified?

 

[JohnW2]

Oh, yes, not questioning that. However, have they both been rectified?

Who knows?! The worry obviously is that if both those faults were present, but only the N-CPC fault has been rectified, 'all might seem well' (in the absence of proper tests) even if a serious deficiency in the earthing remains.

Kind Regards, John