RCB keeps tripping

[spike47]

Hi

I seem to be having a strange problem with my 9kw shower , the RCB keeps tripping every time I switch the main double pole ceiling switch off , it is fine when using the shower but we have to reset the RCB every time someone finish's using the shower . I could understand if the problem was when we switched the shower on , but I can't understand how it happens when it is switched off .

ps: this seems to have started to do this about 2 months ago , nothing new fitted .

cheers

spike

 

[PrenticeBoyofDerry]

Might be worth replacing pull cord isolator, sounds like the two poles are disconnecting at marginally differing times, thus the RCD is picking up an imbalance and tripping
I assume this only happens when the pull cord is isolated, not when you stop showering and turn off at shower?

 

[THRIPSTER]

That's interesting Prentice - please explain how that works?


Regards

 

[spike47]

Might be worth replacing pull cord isolator, sounds like the two poles are disconnecting at marginally differing times, thus the RCD is picking up an imbalance and tripping
I assume this only happens when the pull cord is isolated, not when you stop showering and turn off at shower?

Yes it is when the pull cord switch is de-activated , I can see what you mean , but what would happen if my pull switch was only a single pole ! .

spike

 

[spike47]

Hi

I am going to replace the switch , but I don't think that is the problem , there is no switched load on the pull switch , either when it is on or off , that pull switch in only used to supply the shower switch that is used to switch the shower on and of , the pull switch is switched of after the shower is turned of , so there no current between the contacts to arc or whatever ! .

 

[PrenticeBoyofDerry]

i am thinking may be there is a small capacitive load remaining when turned off, and when isolation takes place the RCD trips. I would also check the isolator for loose conductors. Does the isolator have a neon light?

 

[JohnW2]

That's interesting Prentice - please explain how that works?

It's extremely speculative and, I would say, pretty contentious, but if you search this forum, you'll find interesting discussions about this within the last few months (and earlier). As PBoD has said, the speculation relies upon (amongst other things) capacitive leakage.

Kind Regards, John

 

[Taylortwocities]

That's interesting Prentice - please explain how that works?


Regards

That Kirchoff, he keeps changing his mind. How can a bloke improve himself when the laws keep getting changed.

 

[winston1]

Why do you need to turn off the pull switch after a shower? I only turn mine off when I go on holiday or want to do maintenance work on the shower.

 

[Taylortwocities]

Why do you need to turn off the pull switch after a shower? I only turn mine off when I go on holiday or want to do maintenance work on the shower.

The RCD is there to protect the user of the device.
I would want to investigate this problem, especially as the RCD is protecting a device where water, electricity and a wet body come together.

It won't get better by just not switching it off

 

[spike47]

Thanks guys for all your inputs , just to let you know something , if I leave the pull switch permanently on and just use the shower switch for use then it does not trip ! , very strange .
I don't like to leave the power on to the shower all the time , don't know why , I feel better when there is no neon light shown on it , that's just me I suppose .

spike

 

[JohnW2]

The RCD is there to protect the user of the device. I would want to investigate this problem, especially as the RCD is protecting a device where water, electricity and a wet body come together. It won't get better by just not switching it off

I agree; it's never nice to have something unexplained, particularly when it potentially relates to safety issues, even if there is a 'workaround'. However, I also share winston's uncertainty as to why people bother to turn off shower isolators every day.

However, your earlier comment seems to indicate that you are (like most of us!) very sceptical about the (admittedly pretty 'far-fetched') speculative mechanism as to how operating a DP switch, which has no load, can sometimes cause an RCD to operate - so I wonder what other possible causes/mechanisms you might have in mind.

Whatever, since the issue only arises when the isolator is operated, off load, irrational though it might be, replacement of the isolator (and/or temporary conversion to SP switching) would not, IMO, be a bad starting point.

I might add that, perhaps making some postulated mechanisms slightly more credible, there is not literally 'no load' when the RCD trips - the OP has now indicated that there is a neon in in the isolator (and maybe even a 'power on' one in the shower, which we haven't asked about).

Kind Regards, John

 

[Taylortwocities]

There are a number of threads (many without conclusion) on DIYNOT that have/had this issue. The concluded ones seem to blame a device that has surge suppressor/filter components on the mains input. The collapse of stored energy causing an imbalance on switch off.

But clearly not the case here. The only item could be the neon but that would/should be between line and neutral rather than the lives and earth of a typical mains filter.

I'd side with Prentice and change the DP switch, perhaps to a non-neon one. I'd be interested in the outcome.

 

[JohnW2]

There are a number of threads (many without conclusion) on DIYNOT that have/had this issue. The concluded ones seem to blame a device that has surge suppressor/filter components on the mains input. The collapse of stored energy causing an imbalance on switch off.

Indeed so - as I wrote above, this is not the first time we have heard of, and discussed, such a phenomenon.

But clearly not the case here. The only item could be the neon but that would/should be between line and neutral rather than the lives and earth of a typical mains filter.

I think the (admittedly pretty far-fetched) speculative story goes ... if the DP switch opens neutral first, there might be a path for current to flow from L (still connected) through the neon, then through capacitance (either in cable downstream of the DP switch, or whatever is at the end of the cable) to earth. Such a current would not go through the N side of the RCD so, if adequate in magnitude (even if only transiently) might cause the RCD to operate. ... but, as I have said/implied, such a proposed mechanism seriously stretches my view as to what is credible. In particular, I find it almost impossible to believe that anything approaching 30mA would travel through such a path.

I'd side with Prentice and change the DP switch, perhaps to a non-neon one. I'd be interested in the outcome.

I think we're all agreed on that. Unfortunately, if switch replacement (as you say, probably ideally with a non-neon one) does cure the problem, that would still leave us all speculating about the mechanism of what had been happening.

Kind Regards, John

 

[THRIPSTER]

Why cannot this be due to simple mechanical movement of previously separated cables/ terminals, when operating the switch to the off position, moving a line cable/terminal to touch and earthed part? For example, badly sheathed CPC at DP switch.

Regards