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Parallel TX Tails - Neutral Arrangement

MW (aka Inrush - for those who remember me!)
So this is the new look forum... Impressive!


I have a question regarding AWA transformer tails. I'm looking at a situation where I need three parallel cables per phase.


My question is related to the neutral conductor arrangement. The neutrals need to be installed between the inter-group trefoils in order to maintain equal current sharing. Therefore, I can either have two neutral conductors of slightly larger CSA to give approx. the same CSA as the overall parallel phase conductors. Or, alternatively, three neutrals of the same CSA as the phase conductors split (oddly) between the two groups.


What convention is normally adopted in this situation?


Many thanks in advance.
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    That black book reference, page 16, is as close to maker's instructions as you will get. It seems ERA labs did some tests for Ellis to generate some rating advice.

    A report produced by ERA on behalf of Ellis delivered the following guidelines:Current ratings, given in BS7671, for cables in touching trefoil formation are (also) appropriate for cables in quad bundles. Derating factors, given in BS7671,for cables in touching trefoil formation are (also) appropriate for cables in quad bundles. Voltage drops for circuits in quad-formation should be calculated using the values tabulated in BS7671 for cables in flat touching formation When considering multiple cables per phase, the advice given in Guidance Note No.6 for trefoil groups is applicable to quad bundles. The induced voltage in the neutral conductor of a quad group is minimal and can be ignored.





    So basically by selecting the relevant bits from the tables that are there for trefoil and flat touching , you can create a new column, for quads, and the makers of the cable clamps back you up on it.


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  • 0
    That black book reference, page 16, is as close to maker's instructions as you will get. It seems ERA labs did some tests for Ellis to generate some rating advice.

    A report produced by ERA on behalf of Ellis delivered the following guidelines:Current ratings, given in BS7671, for cables in touching trefoil formation are (also) appropriate for cables in quad bundles. Derating factors, given in BS7671,for cables in touching trefoil formation are (also) appropriate for cables in quad bundles. Voltage drops for circuits in quad-formation should be calculated using the values tabulated in BS7671 for cables in flat touching formation When considering multiple cables per phase, the advice given in Guidance Note No.6 for trefoil groups is applicable to quad bundles. The induced voltage in the neutral conductor of a quad group is minimal and can be ignored.





    So basically by selecting the relevant bits from the tables that are there for trefoil and flat touching , you can create a new column, for quads, and the makers of the cable clamps back you up on it.


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