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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...
  • 0
    I have lost the will and don't feel inclined to go through it all, though a couple of points catch the eye.


    Plasticiser leaching from cable installed in the year 2000?


    As for observation seven ? not just what it says, but the choice of Wiring Regulation that is supposedly contravened.


    Forget trying to calculate the resistance of cables in micro-ohms and condemning cables because they are a milli-ohm adrift, electricians testers are not that accurate.


    You need a new report.


  • 0
    would an 80A MCB be cheaper than a new cable. Less time certainly.

    Really this is not an EICR thing - this is a design review of the kind there may have been  before it was built. It may be that if  full load of 100 amps on all 4 phases really is met, then  the boiler room light dims a bit more than you may expect. I do not see it as serious, as presumably it actually works just fine and has done for years

    I detect a desperate scrabbling about to make work that is not needed. Advising improved surge protection, or better earth bondin and more RCDs are improvements I'd sort of expect in an old building when met with new regs, but not worrying about voltage drops, not unless it is so bad it causes a problem in practice and has been reported as such by users..
  • 0
    I forgot some forum members don’t have a regs book.


    Observation seven condemns a 2.5 mm socket radial circuit that has twenty one outlets, because you can only have one per radial circuit and quotes 422.3.4 Locations with risks of fire due to the nature of processed or stored materials, in particular fire resistant cables, or cables embedded in plaster or concrete, or in conduit.
  • 0
    Its time to move on, I am not sure this forum should be used for this purpose anyway. It was never going to end well-------


    1= The mains-243 volts, should be around 400.

    2= No confirmation of supply polarity,  You ALWAYS start with polarity/phase sequence.

    3= No main bonds on ANY service. Really?

    4= 4 poles, should be triple pole and neutral.


    Get someone else, check them out, make sure they have years of experience. 


    Then get the DNO in to do a mains check.


    Regards, UKPN




  • 0
    mapj1:

    Advising improved surge protection, or better earth bonding and more RCDs are improvements I'd sort of expect in an old building when met with new regs, 




    Surge protection and bonding the lighting protection system to the church electrical installation requires particular attention to detail and specific knowledge, GK told me not to do it without getting a specification from the lighting protection engineer.


    So I expect there should be an observation saying consult the lighting protection engineer about installing surge protection and bonding the LPS- code FI.


    I should add I went on an unexpected 125 mile round trip this afternoon, which gave me three hours to ponder life, work and the universe and I went by a church for which I quoted a rewire and these matters came under discussion, which set me thinking.


  • Former Community Member
    0 Former Community Member
    Sparkingchip:

    I forgot some forum members don’t have a regs book.


    Observation seven condemns a 2.5 mm socket radial circuit that has twenty one outlets, because you can only have one per radial circuit and quotes 422.3.4 Locations with risks of fire due to the nature of processed or stored materials, in particular fire resistant cables, or cables embedded in plaster or concrete, or in conduit.


    And see if you can find that circuit (with 21 outlets noted) anywhere in the report...


  • Former Community Member
    0 Former Community Member
    mapj1:

    would an 80A MCB be cheaper than a new cable. Less time certainly.

    Really this is not an EICR thing - this is a design review of the kind there may have been  before it was built. It may be that if  full load of 100 amps on all 4 phases really is met, then  the boiler room light dims a bit more than you may expect. I do not see it as serious, as presumably it actually works just fine and has done for years

    I detect a desperate scrabbling about to make work that is not needed. Advising improved surge protection, or better earth bondin and more RCDs are improvements I'd sort of expect in an old building when met with new regs, but not worrying about voltage drops, not unless it is so bad it causes a problem in practice and has been reported as such by users..


    And does the cable calc he has made match what the report says is installed in any case?


  • 0
    UKPN:


    Get someone else, check them out, make sure they have years of experience. 





     


    There's a challenge


  • 0
    I am trying to motivate the topic sparkingchip, but I fear its a lost cause

    Regards, UKPN
  • Former Community Member
    0 Former Community Member
    UKPN:

    I am trying to motivate the topic sparkingchip, but I fear its a lost cause

    Regards, UKPN


    Do not fear, the point is taken that we need to get a new report made, and this in hand, but some folks seemed to be enjoying spotting the various errors in the report, observations and recommended works, so I was just providing some pointers to potential new howlers. I am grateful to all that have contributed and confirmed my suspicions. I have been quote astonished at the level of interest it has garnered in fact :-)

     


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