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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)...

248ee514524cf5398885518b2007a96a-huge-image.png


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05733e3016557d58306811936bac5e50-huge-image.png


Many thanks if anyone is able to confirm my concerns or otherwise put me straight...
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  • 0
    So the the murk vanishes with the new pictures.


    Look like someone has gone all over "initial verification" style on an EICR.........................................................................good luck ?


    So a single phase sub DB.


    I asked "steeple" due to being a Church type building. There is something pointy at the top of it?   All my questions were due to "other earthy bits" that may or may not influence things. You still have a mix and match disconnection time thing on some circuits that is odd or just clerical.


    If your Inspector is part of a scheme that verified competency for EICR purposes, particularly commercial, you should follow that enquiry/ complaints procedure if the Report is not presented in a clear manner and they do not clearly substantiate their Observations. It does need to be fit for purpose otherwise there is just conjecture.


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  • 0
    So the the murk vanishes with the new pictures.


    Look like someone has gone all over "initial verification" style on an EICR.........................................................................good luck ?


    So a single phase sub DB.


    I asked "steeple" due to being a Church type building. There is something pointy at the top of it?   All my questions were due to "other earthy bits" that may or may not influence things. You still have a mix and match disconnection time thing on some circuits that is odd or just clerical.


    If your Inspector is part of a scheme that verified competency for EICR purposes, particularly commercial, you should follow that enquiry/ complaints procedure if the Report is not presented in a clear manner and they do not clearly substantiate their Observations. It does need to be fit for purpose otherwise there is just conjecture.


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