DIY Doctor

Wiring in an RCBO

Postby Andy W » Thu Jan 24, 2008 6:26 pm

Real numpty question this one, could any of you wise fellows tell me if it's OK to trim either of the RCBO fly leads ( neutral or earh) to length ( Wondered if they had to be equal length for some bizarre reason
Andy W
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Postby ericmark » Thu Jan 24, 2008 11:06 pm

I can't see any reason why they shouldn't be trimmed but wait in case someone else knows something different.

Postby sparx » Thu Jan 24, 2008 11:22 pm

Hi, no technical reason not to unless ends have nice 'bootlace' ferrules fitted to make good connections,
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Postby Andy W » Fri Jan 25, 2008 12:57 pm

Thanks for your help Ericmark and Sparx.
Could I be cheeky and ask you guys one more question about your latest views on consumer units on a TT-earthed house (pardon the grammer)
could you recommend the best / cheapest / current 17th edition compliant arrangement for RCDs. From what I can gather, a split load board with main incomer replaced with time delayed 100ma RCD , with a 30mA RCD for sockets might do the business. But I wonder if the 17th edition might change this , or whether we'll be forced to incorporate (expensive ) RCBOs.

Thanks again
Andy W
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Postby ericmark » Fri Jan 25, 2008 4:48 pm

Sorry as yet I have not got a copy and I need to order direct from IET to get my 20% discount. The 100ma RCD's were expensive anyway due to not coming with the consumer unit. And I do know there are some changes as to how the cables are protected so in a house with thin partition walls you may need to have lights on 30ma RCD. But saying that well before any regulations said you needed RCD's I had added circuits to my house from a second consumer unit. Both being feed from two 4 way wide RCD's both 30ma and they have been fitted for 25 years. The only time they seem to trip when they shouldn't is with computers with switch mode power supplies which of course did not exist when first fitted. I have at work used UPS's which stopped them tripping the trips. Any other trip has been for good cause. Bath overflowing and water running through light fitting etc. So I am not convinced there is any need for split board. And yes if a 6 way consumer unit costs 4 times the price with RCBO's I can see a problem. As to time delay I have never found regulation allowing this although I have used them many times with up to 1 second delay and 1 amp tripping currents but these tend to be the type where the CT is not built into the Mounded breaker but is wired in together with control box and really are more to do with supply and motor protection and even with 5 earth leakage trips from 5 amp to 30ma and 1 second to 40 mili-second when a nail goes through the cable it takes them all out not just 30ma so having so many was really pointless.

Postby 333rocky333 » Fri Jan 25, 2008 7:46 pm

Think you will find a new style board may be adopted , a board with 2 main rcd's
with an isolator in the meter tails

It will have 100 ma for half house lighting etc and a 30ma for other half sockets etc

Crabtree ones are out so look there

With your adapted split load board, your way your 30 ma rcd would be fed via the 100ma rcd
With the new boards they would be independant
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