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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...
  • Former Community Member
    0 Former Community Member
    Incidentally, if anyone who has kindly responded on this topic is interested to quote to carry out the re-inspection, then you are of course most welcome to drop me a private message to that effect.

    The property is in Chelmsford, Essex.

    You are mostly all quite familiar with the installation now, so probably an easy quote for you :-) 


    Oh - by the way - only competent, experienced electricians who are members of a recognised professional body need apply ....

  • 0
    Peter S3:

    The property is in Chelmsford, Essex.


    I had just worked that out! A clue is "supply to baptist heater panel" in DB MP1.


    Your redaction is still not perfect. I suppose a 36 mile journey from Sidcup was perfectly reasonable in 2015.


    Incidentally, should the circuit be RCD protected? Is the baptism pool a bath, or a swimming pool or other basin?


  • Former Community Member
    0 Former Community Member
    Chris Pearson:


    Incidentally, should the circuit be RCD protected? Is the baptism pool a bath, or a swimming pool or other basin?



    That's the supply to the heater control panel only I think.  The heater circuit itself may be internally protected by the control circuit, or be SELV/PELV I suppose?


  • 0
    Peter S3:
    Chris Pearson:


    Incidentally, should the circuit be RCD protected? Is the baptism pool a bath, or a swimming pool or other basin?



    That's the supply to the heater control panel only I think.  The heater circuit itself may be internally protected by the control circuit, or be SELV/PELV I suppose?




    I think that if I were reporting, I would want to know more about the heater by having a good shufti. 


    Any other views on this particular question?


  • 0
    "Incidentally, should the circuit be RCD protected? Is the baptism pool a bath, or a swimming pool or other basin? "


    Could it be already protected under an Act of God?
  • Former Community Member
    0 Former Community Member
    Peter S3:

    Incidentally, if anyone who has kindly responded on this topic is interested to quote to carry out the re-inspection, then you are of course most welcome to drop me a private message to that effect.

    The property is in Chelmsford, Essex.

    You are mostly all quite familiar with the installation now, so probably an easy quote for you :-) 


    Oh - by the way - only competent, experienced electricians who are members of a recognised professional body need apply ....

     


    Hi Peter, did you find out why the previous company did not do the new EICR?


    Perhaps the trustees should consider Budgeting a rolling yearly check and test of 1/4 of the installation done yearly?


    Best of luck :)


  • Former Community Member
    0 Former Community Member
    weirdbeard:
    Hi Peter, did you find out why the previous company did not do the new EICR?



    No comment - I wasn't involved at that stage.  I have now made good contact with the actual inspector that carried out the 2015 inspection, and hopefully will be receiving a quotation from him (as well as 2 others) to carry out a new EICR.


    I hadn't realised that a rolling 'partial' inspection was a thing - I will certainly explore that with whomever we select to carry out the new EICR.


    Regards,

    Peter.


     


  • 0
    Sparkingchip:

    For an installation that appears to have been installed around the 1960's the EICR from five years ago was remarkably free of observations, whilst the latest EICR has some unconvincing observations. 


    Quite so!


    Observation 4: "37 power circuits have an absence of RCD (411.4.9; 411.5.2; 531.2)". That may be so, but 411.4.9 disappeared with 18th Edn; 411.5.2 concerns TT installations; and Chapter 53 is very different. However, there are plenty of socket circuits without RCD protection.


    Observation 10: "FF3/C17 untraceable (Left isolated for further investigation)." Yes but what about the other unidentified circuits?


    More to the point, why did the 2015 sparks not comment on these issues?


  • 0
    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 


  • 0
    To my mind, the software is a poor reflection of the BS 7671 model forms. How old is it?

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