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Topic Title: radial from a ring
Topic Summary: ??
Created On: 24 January 2013 03:24 PM
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 24 January 2013 03:24 PM
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shrek

Posts: 130
Joined: 09 February 2008

is there a problem with using a 4mm cable off a ring circuit to supply 4 double sockets?
 24 January 2013 03:33 PM
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AJJewsbury

Posts: 11497
Joined: 13 August 2003

If the load justifies the use of 4mm2 then they problem you've got is that it's applied to a single point on the ring (rather than being distributed around it) - so there's an increased risk of overloading the shorter leg of the ring - unless the point of connection is close to the centre of the ring.

Say it's a 30A load, connected 1/4 of the way around the ring, then you'd expect the long leg to carry 10A and the short leg 20A. Any further loads on the short leg and it would be overloaded.

Supplying the 4 sockets via a 13A fuses spur makes sure that can't happen (but of course is only acceptable if the anticipated load is < 3kW).

- Andy.
 24 January 2013 03:42 PM
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shrek

Posts: 130
Joined: 09 February 2008

thanks for reply its only for bedside sockets so no great load only using 4mm as 32amp mcb.
 24 January 2013 03:56 PM
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AJJewsbury

Posts: 11497
Joined: 13 August 2003

Obvious answer is to make it a 13A fused spur then - and save yourself the cost of 4mm2 cable

- Andy.
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