10mm sq Phase CPC

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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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 <= 0.30 ohms (Table 41B2) Assuming 10mm² phase and CPC conductors... 10mm² cable is 0.0044 ohms/metre (two core, Table 4D2B) This is using up 0.132 ohms of your allowed 0.30 ohms Zs. You would have to prove the Ze at the start of the run was less than 0.168 ohms to use even 10mm² CPC, which is unlikely. Therefore you are almost certainly going to have to fit a 3-phase RCD to the start of this circuit to meet the required disconnect time on a short to earth, even with 10mm² phase and CPC conductors.
However, with an RCD fitted, you can then reduce the CPC size, as the RCD will be providing the earth fault loop protection rather than the MCB. The RCD can be rated more than 30mA, providing it is not also required to provide protection against electrocution.
A quick check on voltage drop shows it is within allowed range if that is the only significant part of the cable run between the supply and load.

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.
--
Andrew Gabriel

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     snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) writes:

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.
--
Andrew Gabriel

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(Andrew Gabriel) writes:

use 32 will be tight, no chance with 25
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