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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
    In the FF1 for example, the 'Zs at this board' is recorded as 0.08 Ohm.

    Circuit 1/L1 records 'Continuity R2' as being 0.1 Ohm.

    'Maximum measured Zs' for this circuit is recorded as 0.04 Ohm - less than the R2 for the circuit itself. Can this happen? 


    Circuit 3/L3 has a 'Continuity R2' recorded of 0(?), or 'R1 + R2' of 0.01, and yet a 'Maximum measured Zs' of 0.4 Ohm. I would have expected the measured Zs to be very close to 'Zs this board' + R2. (neglecting the fact that he has managed to find an impedance-less conductor linking two Distribution Boards.
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  • Former Community Member
    0 Former Community Member
    In the FF1 for example, the 'Zs at this board' is recorded as 0.08 Ohm.

    Circuit 1/L1 records 'Continuity R2' as being 0.1 Ohm.

    'Maximum measured Zs' for this circuit is recorded as 0.04 Ohm - less than the R2 for the circuit itself. Can this happen? 


    Circuit 3/L3 has a 'Continuity R2' recorded of 0(?), or 'R1 + R2' of 0.01, and yet a 'Maximum measured Zs' of 0.4 Ohm. I would have expected the measured Zs to be very close to 'Zs this board' + R2. (neglecting the fact that he has managed to find an impedance-less conductor linking two Distribution Boards.
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