Elec Shower trips when OFF

[JohnW2]

Sorry but I can't agree with your analysis. ... It would seem pretty odd to me for a MCB to trip seemingly randomly when there is no load and yet hold in when subject to pretty much full load. I guess it's not beyond the realms of possibility that there is a mechanical problem with the latch mechanism in the MCB or something which causes it to drop out randomly regardless of load but it seems unlikely to me.

Definitely odd, and unusual, but it seemed to me a lot more likely than any of the alternatives (such as the one you postulate). I also wonder whether it really is tripping when there is no load - it could possibly be that the OP only becomes aware that it has tripped when he finds that the shower isn't working (he has said that the 'shower CU' is outdoors, so he's probably not looking at it all the time) and that, in fact, it sometimes trips instantly on 'switch-on' of the shower. Also, as has been said, it's possible that loads other than just the shower are fed from that MCB, so there may be some load when it is tripping, even if it is not tripping on 'switch-on' of the shower.

I personally think the most likely explanation is that there is a wiring fault somewhere. E.g. wires that have lost their insulation or a metal object has penatrated them leading to metal which is nearly but not quite touching most of the time. In those circumstances a bit of movement of moisture (dry air has a MUCH higher breakdown voltage than damp air) could easilly be the difference between an effective open circuit and a near dead short.

I have to say that I would regard that as 'pretty odd' as well. It really would have to be something approaching an (intermittent) 'dead short' (i.e. low enough impedance to produce a magnetic trip) since, otherwise, the persistent high current through the fault needed to trip the MCB (if non-faulty) would probably produce smells, smoke or even flames - and I really do very seriously doubt that moisture/whatever could result in such a low impedance intermittent fault, even if all the conductors were bare. Furthermore, the arrangement of T+E cables is such that it would seem very unlikely that the sort of fault you postulate could result in (intermittent) extremely high currents flowing between L and N without enough getting to the CPC to trip the RCD. However, I accept that 'anything is possible'.

If you are lucky the resistance when the fault is "open" may be low enough to show up on an insulation resistance tester but if you are unlucky it may well be the only way to find the fault is an inspection of the entire length of the cicuit. ... I would suggest starting with insulation resistance tests and a through inspection of all accessible parts of the circuit.

We are told that two electricians have already checked the circuit and found no faults, and one would hope that at least one of them will have undertaken IR tests. Given the circumstances, I would certainly expect an electrician to undertake IR tests before changing the MCB (which is one reason I suggested that it was not a DIY job), but I suspect/fear that those tests will not reveal any abnormality - and I wonder whether, in that situation, one really could justify "examining the entire length of the circuit" (which could be very disruptive) in search of a fault which may well not be there.

Whatever, it needs an electrician.

Kind Regards, John

 

[bernardgreen]

Could some one be turning the MCB off by hand ?

 

[JohnW2]

Could some one be turning the MCB off by hand ?

Good point/question!

... and I think that we need Aquaman to clarify the tripping business - is he aware that the MCB has tripped before he tries to use the shower, or does he become aware that it has tripped when he discovers that the shower is not working?

Kind Regards, John

 

[Aquaman]

****EDITED****

I can confirm that the shower is tripping during times when it is off.....sometimes hours after it been used. Not tripping when switched on and not tripping when switched off. Nobody is manually switching it off as it is in a locked cupboard outside which only I have access too. Nothing else is attached to this RCB 100% sure.

Its seems most likely that again it the isolation pull switch, as although I can see no visable damage (wires blackened etc) it has already been replaced twice in 5 years.

Would replacing the switch this time with a 50amp instead of a 45amp help?

 

[JohnW2]

Its seems most likely that again it the isolation pull switch, as although I can see no visable damage (wires blackened etc) it has already been replaced twice in 5 years.

Nothing is impossible, but I would very much doubt that a switch with no visible damage would be causing repeated trips of a 40A MCB. Was there visible damage (to switches or wires) when the previous two were replaced?

Would replacing the switch this time with a 50amp instead of a 45amp help?

It certainly wouldn't do any harm, but it's unlikely that it would make any difference.

Are you able to answer the question I asked in my most recent post?

Kind Regards, John

 

[Aquaman]

Its seems most likely that again it the isolation pull switch, as although I can see no visable damage (wires blackened etc) it has already been replaced twice in 5 years.

Nothing is impossible, but I would very much doubt that a switch with no visible damage would be causing repeated trips of a 40A MCB. Was there visible damage (to switches or wires) when the previous two were replaced?

Would replacing the switch this time with a 50amp instead of a 45amp help?

It certainly wouldn't do any harm, but it's unlikely that it would make any difference.

Are you able to answer the question I asked in my most recent post?

Kind Regards, John

Sorry John must of been editing my post to answer your question when you replied (see edit)

 

[JohnW2]

Are you able to answer the question I asked in my most recent post?

Sorry John must of been editing my post to answer your question when you replied (see edit)

No problem ...

****EDITED**** I can confirm that the shower is tripping during times when it is off.....sometimes hours after it been used. Not tripping when switched on and not tripping when switched off. Nobody is manually switching it off as it is in a locked cupboard outside which only I have access too.

Fair enough. I just want to be sure that I understand how you are becoming aware of these trips - are you saying that you make frequent visits to this 'locked cupboard outside' and sometimes find that, having previously (after last use of shower) not been tripped, the MCB has subsequently tripped before you have attempted to use the shower again?

You previously described this 'locked cupboard outside' as the 'meter cupboard'. Is this a standard outdoor meter enclosure (to which 'half the world' have keys, and which can be opened with simple tools, anyway) or something with more substantial security (such as a padlock)?

Nothing else is attached to this RCB 100% sure.

As bernard observed, there appear to be three cables going into the top of the enclosure, which one might suspect were '1 in and 2 out' - are you really 100% sure?

Kind Regards, John

 

[Aquaman]

Yep John...thats the case. Turn shower off after use all OK...then sometime during the next 24 hours it will trip, and I have to go to cupboard to reset.
For example after two showers Tuesday morning didn't trip at all. Two showers this morning all OK hadn't tripped during the half hour before leaving then go out and come back two hours later and its tripped!

It is just a stardard meter cupboard. I Live in a good area and can't think what joy anyone would get flipping the switch most days?? No children about, no irate neighbors.

The only reason I am 100% that it only serves the shower is because when the switch has tripped everything else electrical in the house works (except the shower) The only other electrical work which was done at the same the shower was the install of downlighters in the bathroom.....but these all definetley work when the switch has tripped

 

[JohnW2]

Yep John...thats the case. Turn shower off after use all OK...then sometime during the next 24 hours it will trip, and I have to go to cupboard to reset.

How do you know that it's tripped and that you need to go to the cupboard to reset it?

For example after two showers Tuesday morning didn't trip at all. Two showers this morning all OK hadn't tripped during the half hour before leaving then go out and come back two hours later and its tripped!

OK, that's more convincing. Do I take it you're saying that you deliberately looked, and found that it had tripped, even though no-one had attempted to use the shower since it was last working?

It is just a stardard meter cupboard. I Live in a good area and can't think what joy anyone would get flipping the switch most days?? No children about, no irate neighbors.

I agree it's improbable, but bernard was right to point out that these things 'do happen', for whatever reason!

The only reason I am 100% that it only serves the shower is because when the switch has tripped everything else electrical in the house works (except the shower) The only other electrical work which was done at the same the shower was the install of downlighters in the bathroom.....but these all definetley work when the switch has tripped

Fair enough - but can you confirm that, as appears to be the case in the photo, three grey cables appear to enter/leave the top of that enclosure?

Kind Regards, John

 

[Aquaman]

Yep John...thats the case. Turn shower off after use all OK...then sometime during the next 24 hours it will trip, and I have to go to cupboard to reset

How do you know that it's tripped and that you need to go to the cupboard to reset it?

Power light on shower unit and neon switch are unlit

 

[JohnW2]

How do you know that it's tripped and that you need to go to the cupboard to reset it?

Power light on shower unit and neon switch are unlit

Fair enough!

Returning to practicalities, my inclination would be to get an electrician to undertake IR tests (probably 'again') and confirm that the MCB is not supplying anything else. If that's all OK, then the choices would be either to replace the MCB and see if that cures the problem (two or three quid for the MCB and probably 5 minutes' work) or, as plugwash suggested, expose the entirety of the cable run in search for a fault/damage which might conceivably be present (even though I personally doubt it).

Although 'tampering' is probably very unlikely, you might also consider doing something (e.g. with bits of cotton or tape?!) to make any opening of the meter cupboard evident!

Kind Regards, John

 

[gman76]

Looking at the picture there seems to be three grey cables going in the top of the unit. Could there be something else that is fed from this MCB ?

but can you confirm that, as appears to be the case in the photo, three grey cables appear to enter/leave the top of that enclosure?

That looks like two tails & one T&E to me!

 

[JohnW2]

That looks like two tails & one T&E to me!

It could be. Mind you, even if there were a second load, that in itself would obviously not explain the MCB trips. I have to say that, provided that tampering can be ruled out, my money would still be on the MCB being duff - albeit I accept that this is pretty odd behaviour for a faulty MCB.

Kind Regards, John

 

[DaveHerns]

If he knows it's tripped because the power light goes out , doesn't that mean he's not turning off at the ceiling pull switch and it's live as far as the shower until the breaker trips? I was thinking it was tripping with the ceiling switch off but maybe I'm being dense

 

[canduit]

After you have turned off shower, do you then pull the isolator switch? Or is this left on all the time?