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Recommended checks before CU change

Former Community Member
Former Community Member
As most of you know I’ve only been qualified for just over a year and I’ve got a quote to do for a cu upgrade.


I know I’m nowhere experienced enough to do EICR’s yet, but what would you guys recommend I check/test before doing the cu upgrade and should I do these checks/tests at the quote stage?
  • Fitzy, this is what you have ostensibly, an old Wylex metalcald consumer unit.

    https://www.youtube.com/watch?v=0L0p5Rk7hZU


    Please pull the main fuse before staring work and get it resealed after you have finished. You do not want to be dismantling a live Henley block, it is very dangerous.


    Also renew the main earth conductor with a length of 16.0mm2 green and yellow. It is easy to do.


    Z.


  • Former Community Member
    0 Former Community Member
    Z, on my visit I did notice that the seal fairy had already visited the property in the past.  ? ? ?
  • Former Community Member
    0 Former Community Member
    When these boards were installed, would the neutrals be in the same numerical order as the fuses are laid out, or was it just hit & miss in those days?

  • Fitzy71:

    When these boards were installed, would the neutrals be in the same numerical order as the fuses are laid out, or was it just hit & miss in those days?




    The neutrals should be in the correct order relating to the lives, BUT very often are not. If the whole T&E cable can be seen than identification is easy, but if just singles appear that can create i/d problems. The different cable sizes can also help to identify likely suspects. I have been known to turn off and double check disconnection, lock off and temporarily connect a 9 Volt smoke alarm battery to a circuit and test at the consumer unit with a Volt meter to identify cables. All loads must be disconnected of course or they will just short out the battery.


    Z.


  • Fitzy71:

    Z, on my visit I did notice that the seal fairy had already visited the property in the past.  ? ? ?




    That would be after the photos you posted on page 1 were taken that clearly show the DNO seals correctly in place on the cutout, and details of the meter then . . . 


    Regards,


    Alan. 

  • Former Community Member
    0 Former Community Member

    Zoomup:




    Fitzy71:

    When these boards were installed, would the neutrals be in the same numerical order as the fuses are laid out, or was it just hit & miss in those days?




    The neutrals should be in the correct order relating to the lives, BUT very often are not. If the whole T&E cable can be seen than identification is easy, but if just singles appear that can create i/d problems. The different cable sizes can also help to identify likely suspects. I have been known to turn off and double check disconnection, lock off and temporarily connect a 9 Volt smoke alarm battery to a circuit and test at the consumer unit with a Volt meter to identify cables. All loads must be disconnected of course or they will just short out the battery.


    Z.


     




    Am I right in my thinking that the ring final/radial circuits might be in imperial sizes and the cpc could be 1mm2 instead of 1.5mm2?


  • Fitzy71:




    Zoomup:




    Fitzy71:

    When these boards were installed, would the neutrals be in the same numerical order as the fuses are laid out, or was it just hit & miss in those days?




    The neutrals should be in the correct order relating to the lives, BUT very often are not. If the whole T&E cable can be seen than identification is easy, but if just singles appear that can create i/d problems. The different cable sizes can also help to identify likely suspects. I have been known to turn off and double check disconnection, lock off and temporarily connect a 9 Volt smoke alarm battery to a circuit and test at the consumer unit with a Volt meter to identify cables. All loads must be disconnected of course or they will just short out the battery.


    Z.


     




    Am I right in my thinking that the ring final/radial circuits might be in imperial sizes and the cpc could be 1mm2 instead of 1.5mm2?


     




    If ring finals are in imperial sizes they are likely to be stranded copper or even tinned copper. Seven strands for imperial ring circuit live and neutral cables and three strands for the associated C.P.C.s. That would be 7/.029 inch size I believe for the live conductors.


    Original 2.5mm2 twin and earth cable with one solid live conductor and one solid neutral conductor  had 1.0mm2 C.P.C.s. and they were easily broken or damaged.


    Here are some date "milestones" relating to old cables etc.

    http://wiki.diyfaq.org.uk/index.php/Dating_Old_Electrics

    Z.

  • Here is a list of old imperial cables sizes and how they relate to modern metric sizes.

    https://www.daenotes.com/electronics/industrial-electronics/comparison-of-imperial-and-metric-conductor-sizes


    Z.

  • Fitzy71:

    Z, on my visit I did notice that the seal fairy had already visited the property in the past.  ? ? ?




    Apparently these guys fit an isolator for about £60 http://www.hasteltd.co.uk/ Not used them but will think about it for the next job.

  • Former Community Member
    0 Former Community Member
    Hi Fitzy71 , remove the fuseboard cover and make an assessment of the wiring .


    Make sure you have enough neutral and earths to match the line cables.


    Take a sample of accessories off and check wiring looks ok especially obvious additions.


    Run a wander lead from earth bar around all metal accessories and earth contacts at sockets etc.


    Do ring circuit continuity at a convenient socket.


    If all looks good then carry out an insulation resistance test between line/neutral to earth at fuseboard with as much stuff disconnected as possible.


    Chances are you will get low IR , spend abit of time trying to locate reason why ie disconnect neutrals at board.


    If IR is so low that it will cause Rcds to trip then either up yor quote or let Dave down the pub change the board.


    If all reasonable then I also find that a ma clamp meter now comes in handy.


    Clamp the tails and turn everything on , again if high ma reading then you can probably find out which appliance is causing it.


    Make sure you turn on the heating/immersions and timers ,  if pir lighting then if possible tweak it so that you can do a walk test.


    If all ok then change board.


    One point , make  sure the incoming gas and water are not over the other side of the property.


    You dont want to go running new bonding cables around a newly decorated kitchen.


    You can probably do all this for your £90 pre inspection.


    Obviously check Ze.


    Regards