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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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  • 0
    I assume it’s the rubbish software used for this forum, both reports have disappeared.


    With hindsight I should have been able to answer my own question as to whether the existing report was made available to the latest inspector, because it’s a question that is asked and should be answered on the new report. Of course existing reports should be made available to inspectors to allow them to work more quickly and also be able to spot additions, alterations and deterioration within the installation.


    However the latest inspector is not very good at answering questions as can be seen on the schedule of inspections with every item being mark non-applicable.


    I would not get hung up on the matter of how accurate the test meter being used is, because it’s a hell of lot more accurate than the person using it.


    If that calibration certificate dated two days after the testing says it’s accurate and did not need any adjustments it is more valid proof of the accuracy of the tester used than the previous calibration certificate.


     Andy B.
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  • 0
    I assume it’s the rubbish software used for this forum, both reports have disappeared.


    With hindsight I should have been able to answer my own question as to whether the existing report was made available to the latest inspector, because it’s a question that is asked and should be answered on the new report. Of course existing reports should be made available to inspectors to allow them to work more quickly and also be able to spot additions, alterations and deterioration within the installation.


    However the latest inspector is not very good at answering questions as can be seen on the schedule of inspections with every item being mark non-applicable.


    I would not get hung up on the matter of how accurate the test meter being used is, because it’s a hell of lot more accurate than the person using it.


    If that calibration certificate dated two days after the testing says it’s accurate and did not need any adjustments it is more valid proof of the accuracy of the tester used than the previous calibration certificate.


     Andy B.
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