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Can Zs at DB ever be less than the Zs of the feeding circuit?

Former Community Member
Former Community Member
I am reviewing an EICR recently issued for a building with several Distribution Boards feeding sub-Distribution Boards.

I have noted that in some instances, the figure recorded for 'Zs at this board' is significantly less than the Maximum Measured Zs for the circuit recorded on the feeding DB.

e.g. DB FF4 is recorded as being fed from DB FF1.  The feeding circuit to DB FF4 is recorded as having a Maximum measured Zs of 0.4 Ohm, but the 'Zs at this board' for FF4 is recorded as 0.05 Ohm - which is less than the 'Zs at this board' recorded for FF1 (0.08 Ohm) - and which, is in fact, in turn itself less than the 'Maximum measured Zs' for the circuit feeding it.  Can this be true or are there errors in the report?  I thought that cascaded Zs can only get larger due to the added impedance of the feeding circuits? This is not my primary area of expertise, but I am concerned that the EICR is being used to justify the upgrade of several circuits which have passed previous inspections with no problem (hope the resolution of the extracts from the EICR below are sufficient resolution to read)...

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Many thanks if anyone is able to confirm my concerns or otherwise put me straight...
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  • Former Community Member
    0 Former Community Member
    Sparkingchip: I don't know if the 2015 EICR was made available to the new inspector before their inspection.  I presume not, as if it had, they probably would have been able to locate their 'untraceable' circuits - and maybe to query themselves a bit more closely whether a previous NICEIC-approved inspector would really have missed such a major claimed error as a 63A 3ph DB being fed from a 32A 1Ph MCB...

    I am not sure if it is normal practice to provide the previous EICR to a new inspector, or to ensure/require the new inspector to carry out their inspection 'unbiased'? regards, Peter.

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  • Former Community Member
    0 Former Community Member
    Sparkingchip: I don't know if the 2015 EICR was made available to the new inspector before their inspection.  I presume not, as if it had, they probably would have been able to locate their 'untraceable' circuits - and maybe to query themselves a bit more closely whether a previous NICEIC-approved inspector would really have missed such a major claimed error as a 63A 3ph DB being fed from a 32A 1Ph MCB...

    I am not sure if it is normal practice to provide the previous EICR to a new inspector, or to ensure/require the new inspector to carry out their inspection 'unbiased'? regards, Peter.

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