DIY Doctor

Wiring to three sheds

Postby big.dave » Tue Aug 24, 2010 9:40 am

Hi there all im looking to see if my proposed plan is going to be ok or if I need to change anything before I go out and buy anything

I want to run armored cable (I have some heavy industrial stuff) from a socket in my house to a RCD then outside to a junction box under my decking (so i can add deck lights at a later date) then to my main shed aprrox 10 metres away to a 4 way consumer unit then from 16amp MCB to a switch then to a flourescent strip light. or maybe two. then from another 16amp MCB to an outside switch then off to an outside light. then from a 32amp MCB to say 3/4 double sockets inside the shed. then 32amp MCB to another shed and into a double socket. then another 32amp MCB to another shed into a double socket. all wiring outside will be using the 6mm armoured cable and the inside wiring with 2.5mm for the sockets and 1.5mm for the lights. is all this the correct way of doing it or do I need to change anything?
sorry this is long winded, I have explained it the best I can. p.s the socket in my house I will be running cable from is off my kitchen ringmain wich has its own 30amp MCB and RCD unit
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Simply Build It

Postby sparx » Tue Aug 24, 2010 6:18 pm

don't want to p..rain on your parade but you do realise this is all reportable work under LABuilding Regs.
Apart from that what you are considering is a total no-go!
Spuring from a ring can only supply one additional outlet IE one single or double socket.
It is permitted to supply more if fed via a Fused connection unit (Fused spur) which will limit total load to 13A.
As the kitchen ring has rcd protection already fitting a second one in line would be pointless.
ALL work outdoors is a 'controlled service' and can only be done by a registered electrician since even paying LABC's inspection fees up front
£150+ won't give any certificates and no DIYer could afford or know how to use the test instruments required to fill in the IET certs. required by law since 1995.
This really is taking a long time to get through to people, but we are duty bound to point it out.
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Postby ericmark » Wed Aug 25, 2010 2:05 am

If supplied from a 13A RCD FCU then no point in any MCB over 13A so hole system seems flawed.

Even if supplied from the consumer unit then what ever size of MCB supplies the first cable will dictate the size of the rest and they will be smaller of course.

The same applies to RCD's and each RCD will be approx one 1/3 of the size of presiding one as to milliamp rating plus of course the time delay will also reduce if possible.

As a ball park the test equipment will cost around £750 to buy and around £60 to hire. There are some cheap units Socket&see do some plug in units but to have a value rather than pass / fail you are looking at £180 with the simple pass / fail type at around £45 there is one without RCD testing at £35 but that is about the cheapest test device and likely will not be accepted by the LABC.

So to be realistic you need to add around £200+ to the bill for any DIY work that requires Part P notification which means in the main it costs more to DIY than to get an electrician to do the work for you assuming you dig trenches etc.

When supplying out building you do need to consider volt drop, Earth loop impedance, and the method used for earthing. Issue 16 of the IET Wiring matters Autumn 2005 does explain what is required although now a little outdated but it is a good start. Not sure if link will be permitted but if is Google ""

Junction boxes outside are always a problem although I have used them and filled them with re-enterable compound in the main epoxy resin is used so putting a junction for future use does not really make sense.

Although an IP65 box should not allow water in bitter experience tells me it is very hard to maintain the water proof features and water always seems to find a way in.

I think you need to rethink your ideas. It's not as simple as you seem to think it is.
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