RCD trips continuously with water heater

[Tricky Albert]

I have connected up a new 5 KW instant water heater and have used 4mm cable of about 4 metres long to connect to the modern Wylex consumer unit with 2 RCDs using a 32 amp circuit breaker.
The manual for the water heater suggests that it draws 22 amps or so, but the 32 amp breaker was to hand.
As soon as I switch the water heater on, the RCD trips and cannot be reset unless the heater is switched off.
The wiring is correctly installed.
The resistance of the heater element shows as 12 ohms, so I assumed that was OK.
I then disconnected the live and neutral from the element but the RCD immediately tripped out again when the heater was switched on.
I then tried separately disconnecting the live and then the neutral feed to see what happened.
Disconnecting the live feed made no difference, the RCD tripped, but disconnecting the neutral feed allowed the heater to be switched on without tripping the RCD.
I've past my limit of knowledge here and have no idea how to proceed.
Any help gratefully received.

 

[EFLImpudence]

Neutral in wrong neutral bar in CU.

 

[PrenticeBoyofDerry]

As above you have very likely used different splits of the live and neutral bar.

 

[Tricky Albert]

Thanks.
I'll check that out.

 

[PrenticeBoyofDerry]

You are aware that new circuits, need testing, certification and notification?

 

[securespark]

The wiring is correctly installed.

Can you be sure?

EDITED:
Must learn not to post comment before reading to end of thread.
Must learn not to post comment before reading to end of thread.
Must learn not to post comment before reading to end of thread.
Must learn not to post comment before reading to end of thread.
Must learn not to post comment before reading to end of thread.
Must learn not to post comment before reading to end of thread.
Must learn not to post comment before reading to end of thread.
Must learn not to post comment before reading to end of thread.
Must learn not to post comment before reading to end of thread.
Must learn not to post comment before reading to end of thread.
Must learn not to post comment before reading to end of thread.
Must learn not to post comment before reading to end of thread.
Must learn not to post comment before reading to end of thread.
Must learn not to post comment before reading to end of thread.
Must learn not to post comment before reading to end of thread.

 

[ban-all-sheds]

I've past my limit of knowledge here and have no idea how to proceed.

I suspect that that applied before you started the job, and that it's a pity you didn't realise it.

You are aware that new circuits, need testing, certification and notification?

​

If you live in England or Wales you were legally obliged to get Building Regulations approval before you did this work. And the way you did it would not have led to you getting a completion certificate from Building Control.

 

[Tricky Albert]

Thanks for the positive contributions. That sorted the problem.
Shame about the trolls though.

 

[phatboy]

Thanks for the positive contributions. That sorted the problem.
Shame about the trolls though.

I'll translate what you wrote, no thanks required.

I tried what was suggested, and it worked! I am not sure why, but electrical knowledge is not important as it works, what could go wrong?! Also I hate people telling me I should have complied with Building Regulations because I know enough to be dangerous. It is of no concern to me that I have invalidated my home insurance, I saved a few quid bodging and muddling through this myself and that's all that matters! I'll be back next time my lack of knowledge creates a dangerous situation and I don't know why.

 

[ban-all-sheds]

Shame about the trolls though.

I can't see where anybody has tried to create discord here by starting arguments or upsetting people, or has tried to disrupt normal, on-topic discussion, by the posting inflammatory, extraneous, or off-topic messages.

If you brand criticism of your decision that ignorance and incompetence were not good reasons to not fiddle with things you didn't understand as trolling then you make yourself look an even bigger idiot than you already did.

 

[PrenticeBoyofDerry]

Thanks for the positive contributions. That sorted the problem.
Shame about the trolls though.

All contributions on this topic/post made thus far have been valid, to call anyone of the above contributors a troll, is unfair and damn right wrong. It is paramount that the people and pets that reside and visit your property, plus your neighbours are not placed in an unsafe/hazardous environment and we cannot advocate unlawfully activity.

If you are ignorant to what the requirements are, to perform your task legally and safely, we should be thanked/praised for pointing this out to you. Not unfairly branded.
If you require any further help on the topic of legally and safely installing electrical circuits and appliances, do not hesitate to ask. We are here to help not hinder, but occasionally it is evident that the work is beyond the scoop of the person asking the questions. So do not feel harshly treated, if we show concerns regarding this, as it was evident by your original post, that the task had not been performed by someone that has the skill/knowledge to do so. Therefore quite possibly also been performed illegally.