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Principles blank

lyledunn

I am afraid my electrical engineering princIples are letting me down.

So if I have a standard 400/230v star connected secondary feeding an installation that comprises 3 single phase loads of 10A, 12A and 20A for L1, L2 and L3 respectively,    all in phase, no harmonics. I estimate the neutral current to be 9.16A. If I lose the neutral upstream of the loads what is the voltage to earth? Is it less than 55v? 

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    Lyle

    Yes the neutral current is the square route of the sum of the squares minus the sum of the products which is 9.165A. Using my Xcel calculator with a lost PEN the voltage to earth would be 55V.

    Of course this would be for your phase currents if you were a single user off a transformer. If the output of the transformer supplied multiple users then it would not be a balanced supply on the transformer and the loads on the phases would vary continuously. So you cannot rely on the balanced load option for EV charging as a method of protection set out in 722 when connected to a PME supply.

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  • 0

    Lyle

    Yes the neutral current is the square route of the sum of the squares minus the sum of the products which is 9.165A. Using my Xcel calculator with a lost PEN the voltage to earth would be 55V.

    Of course this would be for your phase currents if you were a single user off a transformer. If the output of the transformer supplied multiple users then it would not be a balanced supply on the transformer and the loads on the phases would vary continuously. So you cannot rely on the balanced load option for EV charging as a method of protection set out in 722 when connected to a PME supply.

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