RCD keeps tripping all MCBs are off

grumbler

Section62 said:

grumbler said:

Section62 said:

grumbler said:

RCD can be tripped by a neutral wire touching earth.

But if all MCBs are off it seems to be no current to trip the RCD.

Current flowing on the neutral side to 'earth' would create an inbalance across the RCD and is enough to make it trip (in the right circumstances).

Yes, this is obvious.

The question was in the last sentence of my post that you excluded from the quote - what can cause this current when all live wires are disconnected by MCBs.

This is an example of where the terminology relating to the word 'live' is really important.  The 'neutral' conductor (whilst connected to the supply) is a 'live' conductor - and capable of delivering voltage and current in exactly the same way the (brown) 'live' can.  Thinking that blue=neutral=zero volts is an error... and a cause of confusion in situations like this one.

Capable - yes.

Exactly the same way - no - in practice. The last time I checked this voltage was about 0.01V (with all my MCBs switched on). I'm sure it would be much lower if I switch everything off.

I agree, that it's safer not to assume that it's very low as there can be some fault in the supply.

This is incorrect.  The RCD might be faulty, but this test isn't going to give you that answer.  The neutral conductor is 'live' (see above), hence a current can flow through the RCD and cause it to (quite correctly) trip.

Well, I have to admit (reluctantly) that even 1V voltage between N and E in the supply cable can trip RCD if the contact between faulty wires is good.

bris

How old is the wiring? Could be an insulation problem. Regardless you can't fix this yourself.

Bite the bullet and get someone out to do an EICR, they will find and fix the problem.

Risteard

grumbler said:

Risteard said:

grumbler said:

I do know about LINE and NEUTRAL, but don't like this terminology. By "all" I meant all live wires connected to the appliances/sockets MCB.

I edited my above post - added some suggestion.

It's the correct terminology.

Did I say "incorrect"?

OK, I don't like the 'correct' terminology. And when I say 'live' and 'neutral' instead, everybody understands what I mean and there is no place for any ambiguity.

There absolutely is place for ambiguity, just as if I referred to those two conductors as phase and live.

grumbler

Risteard said:

grumbler said:

Risteard said:

grumbler said:

I do know about LINE and NEUTRAL, but don't like this terminology. By "all" I meant all live wires connected to the appliances/sockets MCB.

I edited my above post - added some suggestion.

It's the correct terminology.

Did I say "incorrect"?

OK, I don't like the 'correct' terminology. And when I say 'live' and 'neutral' instead, everybody understands what I mean and there is no place for any ambiguity.

There absolutely is place for ambiguity, just as if I referred to those two conductors as phase and live.

I don't understand your point.

'live' and 'neutral' vs. phase and live.

Can 'neutral' be mistaken for 'live'?  'Live' for phase?

Risteard

grumbler said:

Risteard said:

grumbler said:

Risteard said:

grumbler said:

I do know about LINE and NEUTRAL, but don't like this terminology. By "all" I meant all live wires connected to the appliances/sockets MCB.

I edited my above post - added some suggestion.

It's the correct terminology.

Did I say "incorrect"?

OK, I don't like the 'correct' terminology. And when I say 'live' and 'neutral' instead, everybody understands what I mean and there is no place for any ambiguity.

There absolutely is place for ambiguity, just as if I referred to those two conductors as phase and live.

I don't understand your point.

'live' and 'neutral' vs. phase and live.

Can 'neutral' be mistaken for 'live'?  'Live' for phase?

My point is that neutral is every bit as much a live conductor as line/phase is. So if you believe that "live and neutral" doesn't have the potential for confusion, then referring to the same conductors as "phase and live" equally must cause no confusion.

Neutral cannot be "mistaken for live" as neutral IS live.