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Can you replace just the RCD, instead of whole consumer unit?

Former Community Member
Former Community Member
My apartment failed it's EICR due to the electrician not being able to trip the RCD in the required time.  I am told that the RCD cannot be replaced and a new metal consumer unit must be installed at a quote of £1180.  The apartment was built in 2003 and seems overly wasteful to ditch the whole unit, however I am not an electrician so would welcome some guidance please before I commit to this remedial action.


This is the RCD currently fitted:
5760S | MK 63 A RCD Switch, Trip Sensitivity 30mA | RS Components (rs-online.com)


It appears it worked within spec for above 30mA, but failed for below, if that helps with whether the whole consumer unit must be replaced.  See report.
Capture2.JPG
  • Former Community Member
    0 Former Community Member
    Chris Pearson:
    LB2:

    I have spoken with another electrician to get a second opinion, he said that the test results seem strange, as the trip responded in 30ms above 30mA as it should, but marked faulty because it didn't trip below 30mA but electrician 2 seems to think that's by design and shouldn't trip with currents lower than 30mA.

     


    I took this to mean that if the RCD is a 30 mA one (or 10 mA) it is tested at 5 times the value, but if it is > 30 mA (100 mA, 300 mA, etc.) it is tested at 1 times the value.


    It need not trip below 30 mA, but should do so rapidly at 150 mA. On the face of it, it has not tripped at all.


     




    Interesting, many thanks.  Apologies if I'm missing something, but as there is only one RCD, shouldn't only one of those boxes be filled?  ie there's one '30mA or below' RCD so the 'Above 30mA' shouldn't have a value in it?


  • Former Community Member
    0 Former Community Member
    Chris Pearson:
    LB2:

    The RCD is separate to the main switch, I now have photographs.  I was mistaken in the RCD type, it is infact an MK Sentry 5760s


    As far as I can see, the product has been discontinued, but there do seem to be some around.




    When looking for replacements, would it matter if I found one from the same MK series with a higher amperage - 80A or 100A?


  • 0
    To test an RCD fully involves more tests at different fault currents.

    I presume it always fires smartly on the test button like you test it every few months... (yeah right...)

    For that model it should always trip at 30mA or above. and  may trip at faults between 15mA and 30mA

    and should never trip below 15mA.

      It is common to test at 30mA and 150mA, and perhaps 15mA as well.

    That is not an IET  standard form, but is presumably  created by some testing sofware, and has most but not all of the same stuff.




    It does look like a discontinued model, but there seem to be a few places still with stock, so if that is the only issue it may well be worth tracking one down.

    One from the same family but say the 80A one should fit just as well - inside the contacts are a bit boskier.

    Mike.

    EDIT  a quick PS to add some pages from the old MK catalog below so you can see all the compatible part nos.
    MK_RCDs1.PNG
    Mk_rcds2.PNG
  • Former Community Member
    0 Former Community Member
    mapj1:

    To test an RCD fully involves more tests at different fault currents.

    I presume it always fires smartly on the test button like you test it every few months... (yeah right...)

    For that model it should always trip at 30mA or above. and  may trip at faults between 15mA and 30mA

    and should never trip below 15mA.

      It is common to test at 30mA and 150mA, and perhaps 15mA as well.

    That is not an IET  standard form, but is presumably  created by some testing sofware, and has most but not all of the same stuff.




    It does look like a discontinued model, but there seem to be a few places still with stock, so if that is the only issue it may well be worth tracking one down.

    One from the same family but say the 80A one should fit just as well - inside the contacts are a bit boskier.

    Mike.


    I phoned MK who advised that either another 5760s or the more readily available 7860s are identical and interchangeable so I will find a new unit for my electrician.  Many thanks


  • 0
    90 minutes.............................


    Warp Drive By


    You get what you pay for.
  • 0
    LB2:

    My apartment failed it's EICR due to the electrician not being able to trip the RCD in the required time.  


    I would recommend a second opinion - get a retest of the RCD.with a proven, calibrated instrument and get a quote for a replacement R.C.D ...... if needed.

    Jaymack    


  • 0
    There’s something’s seriously wrong with that consumer unit.


    Post a picture of the observations page from the EICR, I would really like to see what the “inspector and tester” had to say about it.


    The report ain’t too good either.
  • 0
    It's not the only one which we have seen recently that has two main switches. I reserve judgment on the last two MCBs and RCD without seeing inside.


    Or is there something which I have missed?
  • 0
    I have some brand new  MK RCDs in my van.
  • 0
    I assume that the socket circuits have been taken off the RCD side of the consumer unit leaving all the circuits without any RCD protection, rather than sorting out the problems within the installation. 


    That was probably a dodgy fix carried out quite some time ago, so the installation probably was substandard at the time the EICR was prepared,  which is why it will be interesting to read what the observation are on the EICR.

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