SWA Cable Sizing query

Aug 23, 2006 2 Replies

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fletch1 19 years ago

Hello guys

I have been asked to install a sub main supply cable 25mm SWA 4 core cable from a 63A isolator to supply a distribution board. I am however a little confused as 25mm is huge in my opinion and after checking the regs BS7671 a 16mm cable can handle 77A. Also 25mm will not fit into the terminals of the isolator, I can only assume that the person is talking about the total diameter of the cable. Any ideas are welcome as I have not installed a 3 phase system in a while of this size and it's not making sense to me.

Many thanks

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Mark Rand 19 years ago

A 4 core 16mm^2 SWA cable is (runs out to check the feed to the workshop) 23mm diameter. I think your assumption is correct.

You might have had a quicker response from uk.rec.models.engineering, but it would have been the same response :-)

regards Mark Rand RTFM

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Andrew Mawson 19 years ago

however

There are two issues to consider when sizing the cable: a/ current carrying capacity, and b/ voltage drop. If it is a long run then maybe the large diameter is needed to stay within the permissable voltage drop at full load (I think max allowed is 4% but please check)

AWEM

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