Power in Garage and Fault Tripping ELCB


Postby Stewart7 » Wed Mar 28, 2018 9:22 pm

At present my garage is powered via its own mcb in my consumer unit. The whole house is protected by an ELCB.
At present if there is a fault in the garage, the whole house is cut off. I am currently looking for the fault in a garage circuit that occasionally trips the ELCB. I'm looking for damp or dead spider etc.
As a temporary measure while I am fault finding, could I disconnect the earth between the house and garage and rely on the garage being earthed to the lead pipe of the rising water main and hopefully stop the house going dark because of a fault in the garage?
Or, If I put another ELCB in the garage, will this trip first by being nearer to the fault, or will they both trip.
Thanks for any suggestions
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Postby Mr White » Thu Mar 29, 2018 5:46 pm

Please tell me you have NOT got an ELCB (What does it say on said device?)

No, you can not disconnect the earth, the earth wire on the lead pipe is not to get an earth but to bond the pipe to earth.

I would be inclined to have a "garage consumer unit" fitted in the garage.
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Postby Stewart7 » Thu Mar 29, 2018 7:06 pm

Hi Mr White
Maybe I'm using out of date terminology. What I mean by ELCB is the main switch in my consumer unit that cuts off the mains if there is a leakage to earth from either the live or neutral. Are they now called RCDs?
Mine was fitted in 1988 and has this wording.
MK LN5780, Residual Current Operated Circuit Breaker 30ma trip current.

I am intending to fit a garage consumer unit, but wondered if the tripping device in it would trip before the one in the house, or would they both trip?

Thanks for your help
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Postby Mr White » Fri Mar 30, 2018 1:23 pm

In theory the closet device to the fault should trip, but there is no guarantee this will happen. In an ideal world your garage should be on its own supply so it could not effect the RCD in the house.
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Postby Stewart7 » Tue Apr 03, 2018 5:46 pm

Hi Mr White
Thank you for your help and advice.
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Postby ericmark » Wed Apr 04, 2018 9:48 pm

Your terminology was not wrong, we have ELCB-v and ELCB-c the ELCB-v has been banned, but you clearly have an ELCB-c also called ECCB and RCD. It works by measuring line and neutral and if the same it will not trip, but if they vary between 15 and 30 mA then it will trip.

So connecting a different earth will not make a scrap of difference. If your consumer unit will allow it, fitting RCBO to garage would help, not really a DIY job, but likely if there are for example 4 MCB's on one RCD, you could swap all 4 MCB's for RCBO's and replace the RCD with an isolator, so every circuit has it's own RCD built into the MCB.

However RCBO's are in general longer than MCB's so not all consumer units can be modified.

The main thing is something can be done, but that is not disconnecting earths, that would be at best pointless and at worst dangerous, and since it requires working inside the consumer unit which has live parts which can't be isolated, and it needs testing after with an expensive meter, it is not a DIY job, sorry.
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Postby Stewart7 » Mon Apr 30, 2018 7:07 pm

ericmark wrote:Your terminology was not wrong, we have ELCB-v and ELCB-c the ELCB-v has been banned, but you clearly have an ELCB-c also called ECCB and RCD. It works by measuring line and neutral and if the same it will not trip, but if they vary between 15 and 30 mA then it will trip.

So connecting a different earth will not make a scrap of difference. If your consumer unit will allow it, fitting RCBO to garage would help, not really a DIY job, but likely if there are for example 4 MCB's on one RCD, you could swap all 4 MCB's for RCBO's and replace the RCD with an isolator, so every circuit has it's own RCD built into the MCB.

However RCBO's are in general longer than MCB's so not all consumer units can be modified.

The main thing is something can be done, but that is not disconnecting earths, that would be at best pointless and at worst dangerous, and since it requires working inside the consumer unit which has live parts which can't be isolated, and it needs testing after with an expensive meter, it is not a DIY job, sorry.

Thank you Eric. Much appreciated. Sorry for the long time to reply.
Best wishes
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