RCD tripping to caravan hookup


Postby MikeP » Thu Jul 26, 2007 12:53 pm

I have recently had installed a new beafed up supply to an outbuilding to supply an electric shower, lighting etc and hookups to caravans.

The main dedicated feed from my main incoming supply is via a 30mA DP 63A RCBO and 10mm SWA cable to a new CU with a 100A DP RCBO. The 4 way hookup box is fed from this CU via a 32A MCB and then via 16A MCB to each individual hookup.

Due to recent power outage (momentary cut) the 63A RCBO in the house has tripped. This was reset without any problems but if we had not been available in the house the caravan occupiers had no access to reset this switch. But they do have access to the CU in the outhouse. How do I get this to trip first rather than the one in the house? At the moment the caravan hookup box does not have an RCBO. Would installing one solve the problem. ie this would then be the first to trip and what should the rating be - 32A ??
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Postby BLAKEY1963 » Sat Jul 28, 2007 12:35 am

[quote="MikeP"]I have recently had installed a new beafed up supply to an outbuilding to supply an electric shower, lighting etc and hookups to caravans.

The main dedicated feed from my main incoming supply is via a 30mA DP 63A RCBO and 10mm SWA cable to a new CU with a 100A DP RCBO. The 4 way hookup box is fed from this CU via a 32A MCB and then via 16A MCB to each individual hookup.

Due to recent power outage (momentary cut) the 63A RCBO in the house has tripped. This was reset without any problems but if we had not been available in the house the caravan occupiers had no access to reset this switch. But they do have access to the CU in the outhouse. How do I get this to trip first rather than the one in the house? At the moment the caravan hookup box does not have an RCBO. Would installing one solve the problem. ie this would then be the first to trip and what should the rating be - 32A ??[/quote]

MIKEP
A 32 AMP RCBO COULD BE USED FOR FEEDING 16A HOOKUPS.

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Postby sparx » Sat Jul 28, 2007 4:14 pm

Hi mikep.
A few issues here, regs say only one van per rcd now, has gone down from 6>4>3>1 over the last few years.
to obtain 'discrimination' you need to look at the entire set-up you have.
First do you need an RCD @ house end of outside supply? If so then it needs to be a time delayed version as if you have a number of RCD's, RCBO's in series the first one [upstream] will almost always trip first as they will all 'see' fault leakage of final circuit, but the next one back up the line will see the extra leakage of the additional circuits it feeds, the first one will see these plus the supply cables small leakage, so will'see' worst situation.
one way of helping your set up would be to disconnect earth from house supply cable at outbuilding & install an earth rod in pit, change RCD for main sw.in CU and fit individual 16A RCBO's for each van that's the legal way, plus of course RCBO's for shower & lights.
regards SPARX
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Postby MikeP » Tue Jul 31, 2007 12:25 pm

Thanks both for your advice, which seems a bit conflicting. Sparx quotes that regs now say one van per rcd and blakey1963 says one 32A RCBO is OK to feed 4 outlets via 16A MCBs. Interesting (seehttp://www.raytechinternational.co.uk/) that commercial caravan multivan hookups seem to contravene the latests regs according to sparx. Sound like the regs are not that simple to interpret. Also the part P regd electricial who put in the complete outside system specified a standard (no time delay) 63A RCBO as the first protection at the house end of the outside supply.

The external CU is earthed locally via a new earth rod but the earth from this CU is wired via the SWA cable to the earth in the house. Again as specified by my electrician. Are you suggesting that this earth back to the house is disconnected and I rely on the earth rod to act as the earth for all equipment in the outhouse, ie electric shower, power sockets and lighting?
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Postby sparx » Tue Jul 31, 2007 9:22 pm

Hi Mike P, sure some confusion over numbers sorry if seems worse than it is, my fault! just done a load of installs/inspects. for local authority who insist on one RCD /one van, regs as in guidance note 7, part 8,6,1 to be precise allows for up to 3 pitches per RCD individual MCB's.
Further it says tn-s or TT supply to local consumer unit NOT PME & 100ma time delayed @ supply end of feeder SWA on its own rod at house end then 30ma 'general purpose rcd' at local board with supply cable earth NOT connected to board IE SWA cut back & insulated use a local rod.
There is a note which says "Whilst the PME earth may be connected to permanent buildings in the park, such as toilet blocks, the installation feeding the caravans mustbe part of a T.T. system having a seperate connection to earth independant of the PME earthing system""
Ref. iee reg 608-13-05! WOW! really straight forward eh?
GN7 ISBN 0-85296-995-3 regards SPARX
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