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  1. 03-07-2009 #1
    Dazzol2009
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    Default 17th wiring regs revision Question

    I will be doing my 2382-10 in the coming weeks, got stuck on a question about fault current, not sure if I have been doing too much revision and my brain has gone.
    Anyway question is:
    The fault current due to an earth fault of negligible impedance in a 400v 3 phase, 4 wire circuit, having an earth fault loop impedance of 0.3 ohms.

    The choices are:

    A 1383 A
    B 767 A
    C 124.5 A
    D 72 A

    B is the given answer , do not understand how the answer has been arrived upon, I am obviously missing a formula, can anybody help?


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  2. 03-07-2009 #2
    Mac
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    Default Re: 17th wiring regs revision Question

    You need to find the power factor and power values.I did work it out and it came out with the answer of 767A.
    I=P/(1.732 x E x PF)
    Electrical & Electronics, Ohm's Law, Formulas & Equations

    P= 1333.33
    PF= 0.0025091
    E= 400V
    1.732 x 400 x 0.0025091=1.739. 1333.33 / 1.739 =766.72.Rounded up gives you 767A

    Last edited by Mac; 03-07-2009 at 04:04 PM.
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