Garage circuit


Postby geome » Thu Jan 13, 2011 11:24 pm

I am fitting a circuit into a new garage 7 double sockets + lighting
What is the best circuit to use a 32amp ring main or 20 amp radial.
If I use a 32amp ring main with a new CU in the garage connected to a 32amp Mcb what size circuit breaker should this be connected to in the main house CU
Last edited by geome on Fri Jan 14, 2011 11:24 pm, edited 1 time in total.
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Postby kbrownie » Fri Jan 14, 2011 8:25 pm

What equipment will be used on the socket-outlets?
and where in the UK do you live?
Are you aware of what notifiable work is and part p of building regs and any knowledge regarding BS7671:2008?
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Postby sparx » Sat Jan 15, 2011 6:44 pm

What KB said plus can you produce test certs for the work?
All work outside the main house notifiable to LABC by law.
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Postby geome » Sat Jan 15, 2011 11:06 pm

As I understand it the work will not require notification as it is an attached garage and I have decided to extend part of the original ring circuit into the garage.
THANKS FOR ALL YOUR " HELP? " :evil: :twisted: :lol: :lol:
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Postby ericmark » Sun Jan 16, 2011 9:38 am

Forgetting for moment the law and Part P one needs to consider what you will use in a garage.
If we consider a welding set at 140A output then that will be at approx 32 volt so without considering in rush you will need a 20A supply (Ohms law). So allowing for in rush maybe a little over that.
You are going to fit a consumer unit and you don't want to lose the lights when power trips so the max trip size in the garage consumer unit must be smaller than the one in the house consumer unit.
So if the make of consumer unit will allow you to fit a B25 MCB in garage then using a B32 in house is OK. However if B32 is used in garage then house needs to be B40.

However other than a welding set most other garage items will use less than 13A. In fact I have seen many garages feed with a 13A fuse in a fused connection unit in house and with garage lights feed with a switched fused connection unit with 3A fuse fitted and no garage consumer unit. And all drills, battery charges and other garage type appliances have worked A1.

So the big question is do you want to weld? Personally unless your a welder the problems welding on cars for most DIY people mean it is not worth setting up the garage to be able to weld and in most cases a 13A supply is enough.

However now we return to Part P and the law. The LABC charge over £100 for you to do the work and as a result likely cheaper not to DIY. If not DIY then best option is to ask the guy doing the job what he thinks.
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Postby BLAKEY1963 » Sun Jan 16, 2011 12:11 pm

GEOME

AS kb , sparx and eric have commented about part p , i would check again with your local authority building control , what the situation is
just to be sure.


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Postby kbrownie » Mon Jan 17, 2011 12:55 pm

[quote="geome"]As I understand it the work will not require notification as it is an attached garage and I have decided to extend part of the original ring circuit into the garage.
THANKS FOR ALL YOUR " HELP? " :evil: :twisted: :lol: :lol:[/quote]
You said you were connecting a new CU in garage.
If you are now extending the circuit, you need to be sure you are not going to overload the circuit with industrial like equipment.
You also need to add rcd protection to this circuit, if this is not already supplied at your CU.
This will still need to be inspected and tested, and at least a minor works cert, should be issued.
This will be for every circuit you extend/add to.
So your lights as well.
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Postby jimmy_one_ball » Sun Feb 06, 2011 12:45 am

As a guide to the type of socket outlet circuit you can look at the square metres of floor space of your garage

0 - 50 sq.m = 20A 2.5mm radial circuit

50 - 75 sq.m = 32A 4.0mm radial circuit

75 - 100 sq.m = 32A 2.5mm ring circuit

I'm guessing the first option will be more appropriate in which case 20A for the sockets and 6A for the lights in the garage CU with an RCD type main switch fed by a 4.0mm cable from the CU in the house protected by a 25A MCB

That is making a lot of assumptions regarding the methods of installation and length of run, cable grouping, ambient temperature etc however will more than likely be the case

Just bear in mind you'll have a hell of a job getting someone else to certify it unless you have a periodic inspection done afterwards
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