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Discuss Non-fused spur on A2 Radial Cct ?? in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

M

marshr02

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Can someone help me?

Section 8.2.4 spurs - 17th OSG
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"In ... an A2 radial cct of Table8A a non-fused spur should feed only one single or........."

I was under the impression that spurs only existed on ring ccts i.e they are a 'radial' tap off the ring.

I was intending on installing a 32A, 4.0/2.5 radial circuit. I was expecting to be able to 'branch' the radial cct early on to suit the house layout. Is one branch the radial continued and the other branch deemed a spur and limited to one socket?

I don't see the issue provided the total cable length to each 'leg' of the radial circuit in within spec, hence Zs is within spec. Obviously the 4mm cable is protected by the 32A MCB.

Any help, greatfully appreciated.


- Is the definition of a spur a later addition to an existing circuit?
- Is the definition of a spur a branch off a ring circuit?
 
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W

WarrenG

  • Thread Starter Thread Starter
  • #2
If you have the 17th Edition Regs book - Appendix 15 gives examples of both Ring and Radial Circuit arrangemnets.

However I do believe that there is an update to it so use your logic.
 
M

marshr02

  • Thread Starter Thread Starter
  • #3
Sorry - my boss wont pay for us to get the A4 Red Book - so only have the OSG at the mo. I'll go looking for the chapter you mention - when I get access to a book.

Cheers

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I suspect the answer if because the A1..3 circuits are purposely a general solution for most houses. The limits & contraints on no. of spurs etc are to keep well within all the usual specs; volt drop, Zs, etc, loading, diversity.

If a sparky is happy to ignore 'standard circuits' he is free to design what he wants providing he meets in the design stage all the standard specs?

I'm looking for an experienced sparky to put me out of my misery on this - I've little experience, freshly qualified. Cheers
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Thanks WarrenG - spot on.

Just googled the IET for the errata info for Appendix 15 - they publish this free. It shows exactly what I want.

For those interested in the answer. A 4.0/2.5 32A radial circuit can branch provided cable stays 4.0/2.5. Spurs are 2.5/1.5 - one per.
 
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R

randyrat

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  • #4
Spurs, unfused off a ring to feed only one socket. If fused put as many sockets on the spur as you want. (Obviously the fuse will protect it if you try to overload it)
You can put a spur straight out of the CU on the same terminals as a ring circuit also...this is counted as a spur off the ring, but gives you a lot of freedom compared to running one out of a socket on a ring...maybe this will suit your needs better?
 
M

marshr02

  • Thread Starter Thread Starter
  • #5
Thanks for reply Randyrat. I feel fine in terms of understanding spurs on ring circuits - just a bit confused re radial. WarrenG's post sorted me out.

Cheers Guys
 
M

marshr02

  • Thread Starter Thread Starter
  • #7
Thanks WarrenG - that's the same doc I found a few mins ago. Cheers
 
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