new electric shower problem

[daipwyso]

Hi there. I've just fitted a 10.5kw shower. There was nothing there before. So fitted a Crabtree Starbreaker 63a 30mA RCCB with a 50A MCB, a 16metre run of 10mm T&E feeding the shower via a 20A DP switch. I've plumbed the shower in Speedfit plastic pipe. The only earth connection is via the terminal block in the shower. The problem is that with the DP switch ON everything's ok, but the RCCB trips the instant the shower start button is pressed.
Any help would be greatly appreciated.

 

[vsynth]

Could be a faulty shower unit, or some water could have got into the unit.

That 20A DP switch is rather under-rated , 10.5kW/230V=45.65A

 

[daipwyso]

Hi. Thanks for your reply. Sorry my mistake it's a 45A DP switch. The shower is brand new straight out of the box, what is the likelyhood of it being faulty?
Thanks

 

[plugwash]

How exactly have you wired this new shower CU. Please specify exactly what wires you have connected to where.

 

[daipwyso]

Hi there. The house is 30 years old and everything is original, it has a Wylex rewirable fuseboard. It is my intention - when we're settled in - to get Swalec in to uprate the supply to 100amps and get their advice on upgrading/testing the electrics.
For the meantime I've put a 45A cartridge fuse in the board in place of the redundant cooker fuse. Taken a 10mm live from that to the live terminal of the RCCB. Also taken a 10mm nuetral and earth from the board to the respective terminals in the shower CU. I've taken the live from the shower CU MCB together with a nuetral and earth from the terminals in the shower CU to the feed side of the 45A DP switch. Then taken live nuetral and earth from the load side of the DP switch to the respective terminals in the shower. I hope that's clear enough, thanks in anticipation.

 

[plugwash]

I've put a 45A cartridge fuse in the board in place of the redundant cooker fuse. Taken a 10mm live from that to the live terminal of the RCCB.

bear in mind that the older/smaller wylex boards are not intended to take any fuse/breaker above 30A, that is not the source of your current problem though.

Also taken a 10mm nuetral and earth from the board to the respective terminals in the shower CU.

You don't make it entirely clear from your post what you did with the incoming neutral. It needs to go the neutral side of the input of the RCD, NOT directly to the neutral bar.

 

[Space cat]

I've taken the live from the shower CU MCB together with a nuetral and earth from the terminals in the shower CU to the feed side of the 45A DP switch.

This might be a stupid question, in which case I apologize in advance. Does the neutral return from the DP switch go back through the RCCB?

Edit: Drat and double drat! Pipped by plugwash.

 

[daipwyso]

Hi again. I've connected the incoming nuetral from the fuseboard to the shower CU nuetral bar, also the nuetral TO the DP switch connects to the same nuetral bar! I assume that's incorrect? If I connect the incoming nuetral from the fusebaord to the nuetral terminal of the RCCB; and leave the nuetral to the DP switch connected to the bar, might this solve my immediate problem?
Many thanks for your input so far.

 

[daipwyso]

Hi again, when I've got this sorted out I'm going to work on my spelling (neutral)

 

[Adam_151]

Too much fluffy description going on in here.... we need a photograph!

 

[plugwash]

Hi again. I've connected the incoming nuetral from the fuseboard to the shower CU nuetral bar, also the nuetral TO the DP switch connects to the same nuetral bar! I assume that's incorrect?

indeed

If I connect the incoming nuetral from the fusebaord to the nuetral terminal of the RCCB; and leave the nuetral to the DP switch connected to the bar, might this solve my immediate problem?

it almost certainly will, (it if doesn't it means there is another completely seperate fault to find)

 

[ban-all-sheds]

daipwyso - did you not at any time pause to wonder why you thought it was OK for you to do all this work when you must have realised that you know nothing?

 

[securespark]

[Manuel of Fawlty Towers]

I know nothing!

 

[daipwyso]

Thanks plugwash. I'll make the changes later today and keep you informed.

 

[stargazer]

And how refreshing to get through a whole post about notifiable work where nobody has mentioned Part P