Rcd for shower not tripping

ceekay74

On holding the test button on the showers rcd, nothing happens.

Is this likely to be a problem with the wiring of the shower or do I need to replace the rcd in the fuse box?

I assume this is something I shouldn't just ignore.

Sleeper12

You need to get a registered electrical contractor in to fit a rcbo and test the rcbo, cables and shower. You won't have the equipment to do all of this yourself

Risteard81

ceekay74 wrote: »

On holding the test button on the showers rcd, nothing happens.

Is this likely to be a problem with the wiring of the shower or do I need to replace the rcd in the fuse box?

I assume this is something I shouldn't just ignore.

You need a Registered Electrical Contractor to look at this without delay. If the test button isn't working then the device has failed. Even if it works with metered tests it is required to work on the test button. It could also be a result of a wiring fault.

Risteard81

Sleeper12 wrote: »

You need to get a registered electrical contractor in to fit a rcbo and test the rcbo, cables and shower. You won't have the equipment to do all of this yourself

Not only the equipment but also the legal authority to do it.

ceekay74

Thanks guys. Is this likely to be expensive to sort out?

And should I not use the shower at all?

2011

+1 to the above advice.

ceekay74 wrote: »

Thanks guys. Is this likely to be expensive to sort out?

Assuming that everything else is ok the cost will be made up of the following:

1) Materials. I would expect to pay around €35 for an RCBO (this is a guess, I haven't bought one for a while).
2) Call out fee.
3) An electricians time, should be less than 2 hours.

And should I not use the shower at all?

Don't use it until this is resolved.

Bruthal

Risteard81 wrote: »

It could also be a result of a wiring fault.

If this was the cause of the test button not to work, then the RCD should be tripping during use, especially when the Load it controls is on.

Risteard81

Bruthal wrote: »

If this was the cause of the test button not to work, then the RCD should be tripping during use, especially when the Load it controls is on.

It depends. A neutral/Earth fault can also cause an RCD to be desensitised.

Bruthal

Risteard81 wrote: »

It depends. A neutral/Earth fault can also cause an RCD to be desensitised.

Desensitised to a person receiving a shock if the path involves the shock circuit CPC and neutral fault.

But it would be a strange neutral-earth fault that doesnt trip a 40 amp shower RCD during operation, but desensitises the test button.

Risteard81

Bruthal wrote: »

Desensitised to a person receiving a shock if the path involves the shock circuit CPC and neutral fault.

But it would be a strange neutral-earth fault that doesnt trip a 40 amp shower RCD during operation, but desensitises the test button.

Not really. Depends on impedances and currents involved. If this is a shared RCD as opposed to a dedicated RCD (which of course it shouldn't be for a shower, but that doesn't mean that sometimes it isn't) then this can happen.


A neutral/Earth fault can either cause the RCD to operate immediately or can prevent it from operating correctly. I'm surprised if you haven't come across this.

Bruthal

Risteard81 wrote: »

Not really. Depends on impedances and currents involved. If this is a shared RCD as opposed to a dedicated RCD (which of course it shouldn't be for a shower, but that doesn't mean that sometimes it isn't) then this can happen.


A neutral/Earth fault can either cause the RCD to operate immediately or can prevent it from operating correctly. I'm surprised if you haven't come across this.

Forget impedances and currents as a vague explanation. Just a clear explanation of the mechanism by which a neutral to earth fault on a shower circuit will not trip with 40 amps in on the phase, and dividing at the neutral fault so that less than 40 returns (faulty RCD aside). Genuine question now.

Bruthal

Here's 1 example anyway. 39.971 amps returns on neutral. 0.029 returns on earth via fault. 0.07 of a %.

Risteard81

Bruthal wrote: »

Forget impedances and currents as a vague explanation. Just a clear explanation of the mechanism by which a neutral to earth fault on a shower circuit will not trip with 40 amps in on the phase, and dividing at the neutral fault so that less than 40 returns (faulty RCD aside). Genuine question now.

https://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=42395

Also https://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=107267&enterthread=y

There is one link explaining it, incidentally with an explanation from the erstwhile ETCI. As I say, I'm surprised you haven't come across this phenomenon.

Neutral/Earth faults can be a very serious issue.

I've also seen an installation nearly burn down due to one on a lighting circuit where the neutral tail had become disconnected and so the entire installation load was returning through the neutral/Earth fault on 1.5mm^2 cable (with 1mm^2 cpc) back to the ESB meter.

Bruthal

Risteard81 wrote: »

There is one link explaining it, incidentally with an explanation from the erstwhile ETCI.

Explaining what, desensitized RCD? Nothing to explain. Its very basic why that is, in terms of a person receiving a shock. And, there was no doubt about that point.

As I say, I'm surprised you haven't come across this phenomenon.

The phenomenon of a neutral-earth fault downstream of an RCD not tripping a shower on that circuit? I have. With faulty RCDs. Never seen a Neutral-Earth short not trip on a running shower and functioning RCD, that I can remember anyway. The memory is not great these days though.

You yourself said to me before, that a N-E fault on one circuit will trip RCD with a load on another, when sharing the RCD. This seems to contradict that. My actual response to that was that it depends on the load on the other circuit, which it does. I have performed a few experiments on that in the last 3 decades. I was a bit mad for the experiments...

You also said that N-E short upstream of an RCD can cause them to trip. Again, I`m still waiting on that mechanism of operation to be explained.

As I said, i was asking for an explanation of how an imbalance of 30ma fails to trip a functioning RCD. And if this "phenomenon" causes imbalance of less than 30ma in a 40 amp load circuit with a neutral to earth short, or fault, explain that part.

Neutral/Earth faults can be a very serious issue.

Yes they can

I've also seen an installation nearly burn down due to one on a lighting circuit where the neutral tail had become disconnected and so the entire installation load was returning through the neutral/Earth fault on 1.5mm^2 cable (with 1mm^2 cpc) back to the ESB meter.

And yet a neutral-earth fault on a shower circuit might not cause any imbalance over 0.07 of 1 percent?

Im just curious really. I agree a test button can fail to work due to a N-E fault. But i dont see the shower also running without tripping it, unless the RCD is faulty.

As a sort of fault finding analogy..
A car battery with loose connections. Starter motor wont turn engine over. Owner replaces battery. Now it works fine. Was the original battery faulty, or did replacing the battery simply fix the loose terminations?

Bruthal

Risteard81 wrote: »

I've also seen an installation nearly burn down due to one on a lighting circuit where the neutral tail had become disconnected and so the entire installation load was returning through the neutral/Earth fault on 1.5mm^2 cable (with 1mm^2 cpc) back to the ESB meter.

On this one again, safe to assume it was a neutralized installation?

Bruthal

Risteard81 wrote: »

https://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=42395

Also https://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=107267&enterthread=y

There is one link explaining it, incidentally with an explanation from the erstwhile ETCI. As I say, I'm surprised you haven't come across this phenomenon.

Neutral/Earth faults can be a very serious issue.

I've also seen an installation nearly burn down due to one on a lighting circuit where the neutral tail had become disconnected and so the entire installation load was returning through the neutral/Earth fault on 1.5mm^2 cable (with 1mm^2 cpc) back to the ESB meter.

Ok you added links to forums. I dont have much notion to read other forums.

But It looks like you are linking about RCD tests not tripping RCDs at expected levels due to N-E shorts.

That was never in question, as clearly stated in post #9. Desensitizing happens because earth fault current, or current due to shock in a person, needs to all flow back on the earth to ensure proper operation of the RCD at 30ma levels. That couldnt be simpler.

But it looks like you are applying that logic to a shower circuit having a N-E fault, not tripping the RCD because of desensitizing. That is not the same thing. How can you desensitize something that should NOT trip during normal operation?

Also, desensitizing happens by diverting shock/RCD test (proper test) current back onto the neutral via N-E fault, so reducing the RCD imbalance to less than the total current flow. Where as the shower circuit with N-E fault has some of its N return current missing, and so will trip the shower.


So, as asked already, instead of linking other forums, just explain how 40 amps would flow in on a Phase, through the shower, comes to a N-E short which divides the current, and so less is seen through the RCD neutral, but the RCD does not trip.

Bruthal

Desensitizing an RCD happens when the intended mode of safety operation involves one of its current coils being intentionally bypassed (person receiving a shock, RCD tests, RCD test button), but it is not fully bypassed due to a N-E fault.

Where as a load through an RCD intends to equally use both current coils, but one is partly bypassed due to a N-E fault.

The first scenario reduces the effectiveness of an RCD (desensitizes)

The second causes UNWANTED trips.