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Zs and Ipfc

Former Community Member
Former Community Member

Hi guys,

I have got measured Zs and Ipfc at a 3-phase distribution board from the EICR, but have no information of all upstream equipment including cable lengths/ sizes from the 230V source. 

To my understanding, there's no way I can derive the voltage drop up to that DB from Zs/ Ipfc because I'll need the earth-fault current  or phase-phase impedance. Am I correct?


Second question is: In the same case, say a 1-phase load is supplied by this distribution board, and i'd like to know the prospective short circuit current to check against the disconnection time of the circuit breaker. 

The pscc at the load end cannot be calculated as well because i'll need to know the voltage at the load and total loop impedance?

Thanks!

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    If it is impossible to test the voltage/loop etc at the source, then do your requisite checks at the remote DB. This is a common occurence in industrial premises, where you cannot turn off the power to do a dead test. 

    The supply should be 230v +10%/-6%. See what you have at the DB, then use that figure to calculate your final circuits.

     

    For the single phase DB, the same applies, if you cannot dead test it, you can do a Live test, and use those figures. If it is an ‘always live’ circuit, you may need to do a number of tests at different hours to ensure that connected loads are not unduly influencing your test results.

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  • 0

    If it is impossible to test the voltage/loop etc at the source, then do your requisite checks at the remote DB. This is a common occurence in industrial premises, where you cannot turn off the power to do a dead test. 

    The supply should be 230v +10%/-6%. See what you have at the DB, then use that figure to calculate your final circuits.

     

    For the single phase DB, the same applies, if you cannot dead test it, you can do a Live test, and use those figures. If it is an ‘always live’ circuit, you may need to do a number of tests at different hours to ensure that connected loads are not unduly influencing your test results.

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