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Topic:
RCBO for Electric Shower
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Replies:
24
Pages:
2
Last Post:
Jul 4, 2005 9:33 AM
by:
Stu H
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Replies:
24
Pages:
2
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Stu H
Posts:
52
Registered:
Jun 20, 2005
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RCBO for Electric Shower
Posted:
Jun 20, 2005 4:42 PM
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I have fitted a 10.5kw electric shower to a bath room, This is wired using 10mm2 cable going through an isolation switch and to the consumer unit. Within the consumer unit there was no space on the RCD side so I have used a 45 amp/30ma RCBO though the mains switch,(the RCBO has a functional earth which is wired to the earth point within the consumer unit) but as soon as the electricity is switched on it's trips out, what could be causing this ??
N.B. The Neutral has not been wired into the RCD side of the consumer unit.
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Re: RCBO for Electric Shower
Posted:
Jun 20, 2005 5:14 PM
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So you've got the RCBO fed from the non-RCD side for both L&N, and the shower cable fed by the RCBO. Does it trip with the shower cable not connected?
Have you checked that the cable is OK, and doesn't have a fault somewhere?
You could try, temporarily, moving the shower cable to one of the RCD MCBs (have the shower isolator on but FGS don't turn the shower on) and seeing if it trips the CU RCD. If it does, my vote goes for a dodgy cable. If not, a dodgy RCBO.
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Re: RCBO for Electric Shower
Posted:
Jun 20, 2005 5:33 PM
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All that BAS suggests and when you connected the earth and the neutral conductors from the RCBO did you shorthen them (they are supplied long)? If so some RCBO's have balanced conductors and these should be left at the supplied length (usually they are coiled)
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Stu H
Posts:
52
Registered:
Jun 20, 2005
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Re: RCBO for Electric Shower
Posted:
Jun 20, 2005 5:35 PM
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Yeah, the RCBO is fed from the non-RCD side for both L&N then the RCBO feeds the shower. It didn't trip when I removed the Neutral core from the RCBO.
I haven't physically checked the wiring, but before I could get the RCBO (had to order it) I had wired the shower through a 45a MCB on the mains side of the CU and it's working fine, still is !! It only trips when I connect it through the RCBO.
I haven't tried your suggestion of of moving the shower cable to the RCD side temporarily so i'll give that a go.
The guy in the shop where I ordered the RCBO said that I couldn't return it once I'd wired it in/used it.
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Stu H
Posts:
52
Registered:
Jun 20, 2005
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Re: RCBO for Electric Shower
Posted:
Jun 20, 2005 5:40 PM
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No, i haven't shortened the cables on the RCBO at all, left them as they were in case I have to try and take it back to the shop !! The cables weren't coiled either.
Would the cross bonding of the copper water pipe make any difference. It's in a cupboard outside of the bathroom that then goes into plastic pipe where it meets the shower ??
Thanks for your advice lads.
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Re: RCBO for Electric Shower
Posted:
Jun 20, 2005 6:13 PM
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Ah - if you've got a 45A MCB, you could install it on the RCD side (temporarily moving something to the non-RCD side) and actually run the shower. If that works fine, i.e. does not trip the CU RCD I would start to suspect the RCBO. You could try connecting another circuit to it, e.g. a ring final, to see if that trips the RCBO.
It didn't trip when I removed the Neutral core from the RCBO. Well, it wouldn't, with no current flowing through it...
Would the cross bonding of the copper water pipe make any difference. I sincerely hope not, because if it did that would mean you had an earth leak...
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Re: RCBO for Electric Shower
Posted:
Jun 21, 2005 12:24 AM
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the rcbo wasn't a chint perhaps?
i wired one for a hut supply, didn't work when rcd tester made a fault.
pressed test button on rcd in and it blew up internally
polarity voltage etc was correct . even got a decent earth loop.
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Stu H
Posts:
52
Registered:
Jun 20, 2005
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Re: RCBO for Electric Shower
Posted:
Jun 21, 2005 9:25 AM
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Hi baldelectrician,
What d'you mean by 'chint' ??
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Re: RCBO for Electric Shower
Posted:
Jun 21, 2005 12:17 PM
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Chint. Cheapo brand made in China. Finds favour with sparkies who regard Volex as too up-market for them.
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Stu H
Posts:
52
Registered:
Jun 20, 2005
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Re: RCBO for Electric Shower
Posted:
Jun 21, 2005 2:03 PM
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It's a 'HAGER' RCBO
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Stu H
Posts:
52
Registered:
Jun 20, 2005
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Re: RCBO for Electric Shower
Posted:
Jun 21, 2005 8:31 PM
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Ok, i've wired the shower into a 50amp MCB on the RCD side of the consumer unit, as a tempory measure, and it all works fine - doesn't trip out. I left the RCBO wired in on the mains side of the CU, with nothing connected up to it and it tripped out !!!
I'm now sure it's got to be a faulty RCBO cos it trips with nothing connected to it, would you agree ?
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Re: RCBO for Electric Shower
Posted:
Jun 21, 2005 8:46 PM
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Seems likely.
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Re: RCBO for Electric Shower
Posted:
Jun 23, 2005 8:56 PM
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I've been wondering. What does the functional earth do with an RCBO?
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Re: RCBO for Electric Shower
Posted:
Jun 23, 2005 9:00 PM
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> I've been wondering. What does the functional earth
> do with an RCBO?
Its main purpose is to poke you in the eye whilst installing the RCBO 
Site Admin, UK Electricians Forum
http://supplychain.org.uk/phpBB2/index.php
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Cronos
Posts:
466
Registered:
Nov 2, 2004
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Re: RCBO for Electric Shower
Posted:
Jun 23, 2005 9:17 PM
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AFAIK the load for the test button goes phase/earth instead of phase/neutral as with RCDs.
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