New Extension wiring


Postby Nicktoxic » Wed Sep 03, 2008 1:11 pm

I am renovating an old cottage and have built a new extension, it will include upstairs and downstairs sockets and lighting. Do I have to change the CU to comply with any new 17th edition regs or can I still use my split load CU with the rcd protected side for sockets??

Also the extension has beemed ceilings as original house so can not run cables along joists etc, can I run the cabling along the walls instead?

I would be very gratefull for any assistance

Nick
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Postby ericmark » Wed Sep 03, 2008 6:13 pm

Design date is important if designed before 31st June 2008 you can get away with old regulations but even in old regulations any socket likely to be used outside had to be RCD protected and the bit about splitting into circuits was also still part of the regulations although it didn't say it included RCD it is generally though it hasn't really changed only been clarified. There are zones along the top of the walls where you may bury cables if planning permission or any other building controls unless you have already submitted plans showing the routes of cables I would think you will need to comply to 17th Edition and not to will only delay things as next time you want to do some silly job like adding one socket in a kitchen you will have to do it anyway so may as well do it now and get it over and done with.
Eric
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Postby Nicktoxic » Wed Sep 03, 2008 6:25 pm

Many thanks for your advice, Could you please tell me what the 17th edition has changed in regards to consumer units, are all circuits now protected by RCD? or have I missheard something.

Many thanks
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Postby TOPSPARK » Wed Sep 03, 2008 8:01 pm

Any electrical installation work designed or installed on or after July 1st 2008 must be done to 17th edition wiring regulations. so you might as well install a 17th edition consumer unit. just a suggestion you could do the installation work on the extension by burying metal conduit in the walls and running your supply cables that way and it will give you added protection in case of accidently drilling them
regards
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Postby Nicktoxic » Thu Sep 04, 2008 12:58 pm

cheers, What is the difference with a 17th edition CU please, not taken my 17th edition yet!!!

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Postby ericmark » Thu Sep 04, 2008 1:40 pm

All sockets under 20 amp protected by RCD, Everything in bathroom protected by RCD including lights. The division in to circuits it has been made plain should include RCD. And unprotected wires buried under 50mm protected by RCD. The latter will mean by using Ali-tube cable instead of twin and earth some circuits may not need RCD for example cooker, smoke alarms, immersion heater. Also where a socket has a marked designated use for example marked fridge and only used for fridge it can also escape being RCD protected. But would need surface cable or Ali-tube cable. There are other options like conduit and SWA cable.
It is up to you how to configure the consumer unit. Using RCBOs on all circuits requiring RCD protection and MCBs on the rest a single neutral bar is all that is required. But some prefer to put a group of circuits on a RCD and then twin or triple neutral bars will be required. The all RCBO will comply with the regulations but when grouping items together it is no longer cut and dried some favor fixed wiring on one and sockets on another and some will put down stairs sockets with up stairs lights and the interpretation of the regulations is not so cut and dried and really one would need to make a risk assessment of some sort and being remote to the work I would not like to say how it should be split.
Two criteria have to be considered.
1) Likely hood of non fault leakage tripping the RCD mainly considering filters found in computers etc.
2) Likely hood of danger when any safety circuit i.e. lights and smoke alarm are lost.
In time a standard will evolve but at the moment it is a little up in the air. I have put it this way as you are likely to get conflicting advice. So if the RCBO's will physically fit in your existing consumer unit there is no need to change it. And even if not there are ways to avoid it but if it will not take RCBO's then it is likely to cause problems in the future so changing may still be best option.
But on the whole it is unlikely that an existing split board will not accept RCBOs so you should be able to add 4 or 5 at less than cost of new board and a lot less work so I would think you will not need to change the consumer unit.
I hope that makes sence
Eric
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