10mm sq Phase CPC

Aug 14, 2006 3 Replies
S

Hi there all, Just a little question:



I'm in the UK. 3Ph 415V. I'm installing a compressor in my Garage. The MCB I want to use is 40A, Type D.



The compressor is 415V, 3Ph, 40A. My cable run is 30m in Trunking and Conduit into the Isolator.



I've worked out, via the 16th edition handbook that I need 10mm sq Singles to run from my Distribution board to the 40A Isolator.



Therefore I'll have 5 wires (L1,L2,L3,N and CPC).


1.What size of Earth/CPC should I run to the Machine...10mm sq?
2.Do you think 1x25mm Conduit drop will be OK for the cables... eg.. will they fit?

Thanks loads for your help, Shay



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A

Well, this is my take on it...

On a phase to earth short, the MCB must trip within 5 seconds. For a D40 MCB, this means Zs 2.Do you think 1x25mm Conduit drop will be OK for the cables... eg..

According to the On-site Guide, 4 x 10mm² singles will pull into in a 10m straight run, or a 6m run with one bend, or a 3m run with 2 bends, or a 1.5m run with 3 bends. Personally, I suspect it will be quite tight though.

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A

Oh, I missed that you have a neutral too, i.e. 5 wires. That changes it to a max 3m straight run, or 1.5m run with one bend. To pull any more, you'll need 32mm conduit.

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S

use 32 will be tight, no chance with 25

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