Consumer unit replacement (RCD or Not)


Postby Overthehill » Wed Jul 25, 2007 3:55 pm

Deciding to replace my consumer unit, the board I am replacing is not a split board and the incomer has a 80A 30mA RCD.
In the past suffered nuisance tripping, do I go for a 80A 100mA RCD, or perhaps a split board. Alternatively what if I use an 80A isolator(no RCD). with MCB’s on lights etc and individual RCBO’s to protect my 2 ring mains and the shower unit. All advice gratefully received.
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Postby sparx » Thu Jul 26, 2007 7:44 pm

Hi, O-t-H,
first thing is what method of main earthing cos if it's TT (rod) you must have rcd @ at least 100mA on incoming sw. in which case split bd with 100/30mA rcd's the only way.
If TN then it's a ? of priorities as I see it, I like RCBO's on power circuits, showers etc. but have had difficulty in finding them rated over 32A for most makes of CU.
'Nuisance tripping', can happen sometimes when lamps blow due to inductive surge i'm told altho' quite how that works I have yet to find out!
but good enough reason for not having lights on RCD circuit, this could be interesting next year as draft 17th regs say ALL circuits for bathrooms must be on RCD, even lights!
If tripping caused by other reasons then indicates fault which needs investigating anyway,
So really no straight answer i'm afraid, but i tend to go with your 2nd choice if poss, regards
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Postby Overthehill » Thu Jul 26, 2007 8:28 pm

SPARX To give you additional information the main incoming United Utilities main fuse has a label on its earth terminal block which reads "PME EARTHING SYSTEM TERMINAL". would this affect your choice. Thanks O-T-H.
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Postby sparx » Fri Jul 27, 2007 7:47 am

Hi agn. PME = tn-c-s to is type of tn system so all I said valid,
Have to point out b4 someone else does 'this is Part P notifiable work' so either pay fee, get local authority bldg. control approval b4 starting or get registered leckie to do work,
regards SPARX
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Postby Overthehill » Fri Jul 27, 2007 12:03 pm

Thanks SPARX, intended to use a registered electrician to carry out the work, just wanted to bring myself up to speed and hopefully ensure I replace the existing CU with the best possible option. I have sourced both 32A and 45A MK RCBO’s. So at the risk of being a pain, which would you go for.
Split board with 80A 30mA RCD,
Split board with 80A 100mA RCD
None split board 80A isolator and with RCBO’s on all potentially hazardous circuits.
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Postby sparx » Sat Jul 28, 2007 4:22 pm

Hi agn I like last option, main sw. non-split bd. + RCBO's for skts, showers, outside circuits etc
regards SPARX
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Postby Overthehill » Mon Jul 30, 2007 7:26 am

[quote="sparx"]Hi agn I like last option, main sw. non-split bd. + RCBO's for skts, showers, outside circuits etc
regards SPARX[/quote] Thanks Sparx for your help O-T-H
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