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Topic Title: sub boards
Topic Summary: sub boards
Created On: 26 September 2017 09:08 PM
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 26 September 2017 09:08 PM
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jay321

Posts: 1
Joined: 26 September 2017

rewiring a big domestic house with an out house and garage. i know the main disboard needs a new one. but what size breaker do you normally put on for two sub boards in garage and out house. i cant work out the load of sub boards as client keeps changing there mind so want to give them more than enough to play around with and can i have two sub boards going off main dis board?
 27 September 2017 05:06 PM
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alanblaby

Posts: 747
Joined: 09 March 2012

You size your breaker by the expected load.
1 socket outlet and a light would be fine on 16 amps.
5 sockets and the use of a welder and other equipment may need 40 amps.
Take as many sub boards as you want off a main board.
SWA cable used for the sub boards? Then consider not putting it on a RCD, and have the RCD at the remote end.
Be aware of the earthing system, and how the out-house needs to be earthed, and whether a TT install at the remote end is required.
 27 September 2017 05:21 PM
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weirdbeard

Posts: 3116
Joined: 26 September 2011

Originally posted by: jay321

rewiring a big domestic house with an out house and garage. i know the main disboard needs a new one. but what size breaker do you normally put on for two sub boards in garage and out house. i cant work out the load of sub boards as client keeps changing there mind so want to give them more than enough to play around with and can i have two sub boards going off main dis board?


Welcome to the forum.

Is it a 100A main fuse? If so run tails from the DNO isolator to henley blocks, then tails to main fuse box and a 100A switch-fuse for each sub which should be enough to play around with.

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:beer)
 27 September 2017 05:29 PM
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dustydazzler

Posts: 1342
Joined: 19 January 2016

I ran a 6mm swa to my garage for future proofing re vehicle charger
my old man has 1.5 micc feeding his garage off a 16a mcb which was previously a 15a 3036 and has been like that since the house was rewired back in the 70s
horses for courses
 28 September 2017 10:39 AM
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AJJewsbury

Posts: 15838
Joined: 13 August 2003

I agree with weirdbeard - don't feed a CU from an MCB/RCBO - MCBs won't discriminate properly regardless of their rating - MCBs are meant to be fed from HBC fuses (or MCCBs), not another MCB. Ideally (for proper discrimination) you'd want a fuse rated at at least 60 or 63A - and hence cable size to suit.
- Andy.
 28 September 2017 10:47 AM
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mapj1

Posts: 9366
Joined: 22 July 2004

In some cases you could decide to have a 32A radial and use a switch fused spur as the light switch, and omit the second CU altogether.

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regards Mike
 28 September 2017 12:21 PM
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dustydazzler

Posts: 1342
Joined: 19 January 2016

Agree with mapj1
If you are certain that the out buildings are 'low load' so say anything less than 30a total.
I would just take a radial straight off of a 32a breaker and wire up my sockets in a radial at the out building and use a swi/spu with a 3a fuse for the lighting.
saves you buying 2 separate garage consumer boards , possibly saving you about £80/£90 just on those 2 parts alone.
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