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What is the purpose of Prospective Earth Fault Current measurement in a 3 phase DB

Apostolos

Good afternoon

On a 3 phase DB what is the purpose of measuring the PEFC?

I know we measure the prospective short circuit current between L1,L2,L3 and N and then double the highest reading. 

This is the Prospective Fault Current which is being recorded.

Why should we waste time with prospective earth fault current?

Are there cases where PEFC is higher than PSSC?

Thanks

Parents

  • There will be cases when the earth path is a lot lower than the neutral loop - indeed there are places where supply neutral does not arrive at all, and any 230V supply is derived from L-L by local transformer.

    And the other way about - if the earth impedance is unusually high compared to the neutral loop, then there may be a need for interlocked earth fault trips.
    In effect PEFC is a Zs test revisited.
    Large TT 3 phase supplies are far from unknown once you get out of sub-urbia.

    Mike.

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  • There will be cases when the earth path is a lot lower than the neutral loop - indeed there are places where supply neutral does not arrive at all, and any 230V supply is derived from L-L by local transformer.

    And the other way about - if the earth impedance is unusually high compared to the neutral loop, then there may be a need for interlocked earth fault trips.
    In effect PEFC is a Zs test revisited.
    Large TT 3 phase supplies are far from unknown once you get out of sub-urbia.

    Mike.

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