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MV cable in LV conditions


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#1 johnbthompson

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Posted 08 April 2005 - 09:46 AM

HI,

I have used a 500sqmm MV (11kV) cable (x15) inplace of a 500sqmm LV (600/1000V) (x15) cable for running from a transformer secondary (3.15MVA) to an MCC.

The cable sizing was originally done with the LV cable and LV cable current carrying capacity tables. The current carry capacity of the equivalent MV cable is lower in the MV tables. Therefore I potentially need to use more MV cables to do the job. Questions:

1. Can I use the LV current carry capacity tables for the MV cable - as it is under under LV conditions (460V).

2. If not, why not - why are the current carrying capacities lower for an equivalently sized MV and LV cable.

Thanks,

John.

#2 johnbose

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Posted 13 December 2005 - 10:55 AM

Because derating factors come into play as voltage go up




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