RCD tripping

[JohnnyTheFox2010]

I live in a 5 year old house. About a month ago, the Mira Sport 7.5kw electric shower started tripping the RCD after about 5 minutes of use. I spoke with an electrician who said that it was almost certainly the shower unit itself and that this should be replaced.

i bought a new Mira Sport 9kw electric shower (the electrician confirmed that this would be okay on 6mm cable) and this was fitted by a plumber yesterday. Looking forward to being able to use the new shower today, it tripped the RCD again after about 5 minutes of use!

It clearly wasn't the shower unit at fault and now after spending a couple of hundred pounds on a new shower I probably didn't need, I am confused as to what could be causing the RCD to trip. There was no excessive power use today at the time the shower was being used, so I don't think an overload is the problem.

Has anyone any ideas what could be causing this? It is the RCD that trips, not the particular switch relating to the shower itself.

Any help much appreciated.

 

[conny]

When you say ' It is the RCD that trips, not the particular switch relating to the shower itself.' are you refering to the main RCD tripping meaning all your electrics go off?
What size breaker controls the circuit?
Also I think you will find someone on here will tell you that 6mm² cable isn't large enough for a 9kW shower.

 

[JohnnyTheFox2010]

When you say ' It is the RCD that trips, not the particular switch relating to the shower itself.' are you refering to the main RCD tripping meaning all your electrics go off?

Yes, it's the main RCD (RCCB) that trips and everything goes off. It says 63A 30mA 363/S030 if that helps?

Hope 6mm is okay - the electrician I spoke to said it was, and his company wired the house when it was built!

 

[nozspark]

The only other thing you could do is isolate (turn off) the circuit at the CU and have a look behind your shower isolator switch for signs of burning...

Otherwise you need to get a electrician out to actually test the circuit!

Unless you have the necessary test equipment??

 

[JohnnyTheFox2010]

The only other thing you could do is isolate (turn off) the circuit at the CU and have a look behind your shower isolator switch for signs of burning...

Otherwise you need to get a electrician out to actually test the circuit!

Unless you have the necessary test equipment??

I assume CU is consumer unit? Is the shower isolator switch the switch I refer to as the one not being tripped on the CU? If not, is it the pull switch to turn on the shower in the bathroom? Not at all well up on these things??!

I don't have test equipment so will need an electrician to check. A local guy can't come for a week so am frustrated to know what's wrong in the meantime in case there is something of concern

 

[nozspark]

First off, if you are unsure about what you are doing then leave well alone and get a pro in to have a look... SAFETY is very important, we don't want you getting an electric shock or being electrocuted now do we!!

Now to answer your questions..

Yes CU is consumer unit

Isolator switch could either be a pull cord switch (in the bathroom) or a wall mounted switch outside.... a common fault is the neutral burning out,, that's what I was meaning that you should check!

 

[martinxxxxxx]

Do you have a neon isolator switch in the ceiling controlling the shower?

If you do. Does it trip the rcd when you switch this on without using the shower or does it only trip if the shower is actually showering?

Martin

 

[conny]

I'm not an electrician so could be wrong but I was under the impression that your main RCD is usually 100ma and then individual circuits are rated at 30ma to avoid this kind of occurence.

 

[JohnnyTheFox2010]

First off, if you are unsure about what you are doing then leave well alone and get a pro in to have a look... SAFETY is very important, we don't want you getting an electric shock or being electrocuted now do we!!

Now to answer your questions..

Yes CU is consumer unit

Isolator switch could either be a pull cord switch (in the bathroom) or a wall mounted switch outside.... a common fault is the neutral burning out,, that's what I was meaning that you should check!

Thanks for your concern. Don't worry I'm not going to try anything irresponsible. Electrics frightens the willies out of me

I will have a look but won't attempt to do anything with which I am not comfortable.

Is correcting a neutral burn out (and by that I assume this means replacing the isolator switch unit) an expensive business?

 

[JohnnyTheFox2010]

First off, if you are unsure about what you are doing then leave well alone and get a pro in to have a look... SAFETY is very important, we don't want you getting an electric shock or being electrocuted now do we!!

Now to answer your questions..

Yes CU is consumer unit

Isolator switch could either be a pull cord switch (in the bathroom) or a wall mounted switch outside.... a common fault is the neutral burning out,, that's what I was meaning that you should check!

Thanks for your concern. Don't worry I'm not going to try anything irresponsible. Electrics frightens the willies out of me

I will have a look but won't attempt to do anything with which I am not comfortable.

Is correcting a neutral burn out (and by that I assume this means replacing the isolator switch unit) an expensive business?

 

[Taylortwocities]

I'm not an electrician so could be wrong but I was under the impression that your main RCD is usually 100ma and then individual circuits are rated at 30ma to avoid this kind of occurence.

Yes you are not an electrician.The only time there should be a 100mA RCD as the MAIN SWITCH is if this is a TT installation. We don't know that and it adds nothing to the discussion by mentioning it.

I agree. 6mm² is not big enough for a 9kW load. Maybe 8.5kW on a good day (and with a lot of caveats).


Foxxy, you said

Hope 6mm is okay - the electrician I spoke to said it was, and his company wired the house when it was built

Don't forget that the 6mm was there to support a 7.5kW shower and that was fine. (32amps)

But you have changed things. You have put in a 9kW shower (nearly 40amps).

Can you see where things may have started to go wrong??

 

[nozspark]

If a cable / termination has burnt out then you will need to replace the switch and cut back the cable untill you find a bit that hasn't been damaged

 

[JohnnyTheFox2010]

Do you have a neon isolator switch in the ceiling controlling the shower?

If you do. Does it trip the rcd when you switch this on without using the shower or does it only trip if the shower is actually showering?

Martin

Yes, a neon pull cord isolator switch in the ceiling. It trips only when actually showering, after a few minutes use.

 

[JohnnyTheFox2010]

I'm not an electrician so could be wrong but I was under the impression that your main RCD is usually 100ma and then individual circuits are rated at 30ma to avoid this kind of occurence.

Yes you are not an electrician.The only time there should be a 100mA RCD as the MAIN SWITCH is if this is a TT installation. We don't know that and it adds nothing to the discussion by mentioning it.

I agree. 6mm² is not big enough for a 9kW load. Maybe 8.5kW on a good day (and with a lot of caveats).


Foxxy, you said

Hope 6mm is okay - the electrician I spoke to said it was, and his company wired the house when it was built

Don't forget that the 6mm was there to support a 7.5kW shower and that was fine. (32amps)

But you have changed things. You have put in a 9kW shower (nearly 40amps).

Can you see where things may have started to go wrong??

Thanks but please hold back on patronizing me. I didn't fit it. It was fitted by a qualified plumber after I had asked a qualified electrician that wired the house whether 6mm cable would support a new 9kw shower. HE said that it would.

Please don't assume that this was MY doing!!!!!

Can we remember please that after 5 years of use the original 7.5kw shower started tripping the RCD

 

[bhm1712]

An RCD is not looking for circuit overload.

There must be earth leakage somewhere in the circuit. When the shower was replaced did the plumber check to make sure that the pipe fitting at the shower end is not leaking? i had a shower tripping an RCD once that was caused by water spraying up from an old compression fitting onto the live terminals.

with the fault occuring after a few minutes of use, it sounds to me like a water issue, which dries up by the time you begin to use the shower the next time.

its just strange that it occured with both old and new shower. Hence why i ask if the plumber checked the fitting, as most would just reuse the old.