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

Former Community Member over 4 years ago

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)...

Many thanks if anyone is able to confirm my concerns or otherwise put me straight...

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0 Sparkingchip over 4 years ago

I am intrigued by the software being used to produce the certificates and in particular the schedule of inspections where everything is marked non-applicable.

Currently I am paying to use the Napit Desktop certificate software, when I work down the schedule of inspections and code something it brings up a dialogue box and I can select text for the observation, this then may bring up a second dialogue box to make the observation more specific, so when I go to the observations they are already filled in with specific comments and BS7671 references, I can then edit them and make very specific to the installation that is being inspected and tested. These codes and observations are based on the Codebreakers book, so that can also be used as a reference whilst compiling the report.

It actually becomes difficult to write stupid observations, because you would have to rewrite the observation that has already been inserted to say the wrong thing.

So didn’t the software that was used offer the same features or did the person compiling the report not realise that there is help built into the software or did they just choose not to use the software as designed?

Andy Betteridge
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0 Sparkingchip over 4 years ago

I am intrigued by the software being used to produce the certificates and in particular the schedule of inspections where everything is marked non-applicable.

Currently I am paying to use the Napit Desktop certificate software, when I work down the schedule of inspections and code something it brings up a dialogue box and I can select text for the observation, this then may bring up a second dialogue box to make the observation more specific, so when I go to the observations they are already filled in with specific comments and BS7671 references, I can then edit them and make very specific to the installation that is being inspected and tested. These codes and observations are based on the Codebreakers book, so that can also be used as a reference whilst compiling the report.

It actually becomes difficult to write stupid observations, because you would have to rewrite the observation that has already been inserted to say the wrong thing.

So didn’t the software that was used offer the same features or did the person compiling the report not realise that there is help built into the software or did they just choose not to use the software as designed?

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

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