Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 80 replies
  • Subscribers 32 subscribers
  • Views 6398 views
  • Users 0 members are here
Options
You may also be interested in
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Obvious departures from the regulations at first glance at a new consumer unit.

Jaymack
I was asked to give an EICR on an domestic property which is to be placed on the market (part P applicable). I found that a builder as part of the other renovation work, (new doors, windows and kitchen etc.) has carried out the installation of a new metal consumer unit. On first opening this dual RCD unit, the 2 lighting circuits were on one R.C.D., and the 2 final ring circuits on the other R.C.D,, it was obvious also, that some wires to the new CB's were short and not lengthened, resulting in a bird's nest at the M.C.B.''s.


Plainly, a qualified electrician hadn't carried out the work. What would the readers as registered electricians have done ?. 1. Walk away. 2. Propose to have an E.I.C.R. carried out (UNSATISFACTORY), then carry out the rectification work and issue MWC's.3. Rectify the obvious departures, issue M.W.C.'s and then issue a SATISFACTORY E.I.C.R. 


Jaymack
  • 0

    Au contraire the noo - See 314.1 (i).



    Au contraire contraire - 314.1 is only about the division of the installation into circuits - circuits are define by overcurrent protective devices - so RCDs are irrelevant to that. (If that wasn't the case we wouldn't be allowed one RCCB feeding multiple MCBs).


    314.2 might be of more interest - 'due account shall be taken of the consequences of of the operation of any single protective device' - but that doesn't say though shall or shalt not, just that you should think about it a bit.


      - Andy.
  • 0

    Is there a requirement for MCBs to have reducing ratings working away from the RCD? ie, in reverse order: 40, 32 , 32......16,..6, 6  Or just common practice?



    Just good practice as far as I'm aware - if the larger currents involve only the shorter lengths of bus-bar then the overall heating is minimised. Pretty minimal effect in any event I would have thought.


       - Andy.
  • 0

    Jaymack:

    On first opening this dual RCD unit, the 2 lighting circuits were on one R.C.D., and the 2 final ring circuits on the other R.C.D,, it was obvious also, that some wires to the new CB's were short and not lengthened, resulting in a bird's nest at the M.C.B.''s.




    If you had a CU with two RCDs and four MCBs for upstairs ring main (32A), downstairs ring main (32A), kitchen ring main (32A), and outside socket (16A) then how would you connect them up, and why? If you then had to add circuits for a cooker (32A) and a central heating boiler (16A) which RCDs would you connect them to, and why?


  • 0
    Upstairs lights and downstairs sockets.


    Downstairs lights with upstairs sockets.


    The central heating boiler circuit isn’t really needed it adds to the abundance of circuits which are probably hard to justify. If you were installing arc fault detection devices at  well over a hundred quid a piece it would focus your mind on how many circuits you really need.


    Andy Betteridge
  • 0

    AJJewsbury:




    Is there a requirement for MCBs to have reducing ratings working away from the RCD? ie, in reverse order: 40, 32 , 32......16,..6, 6  Or just common practice?



    Just good practice as far as I'm aware - if the larger currents involve only the shorter lengths of bus-bar then the overall heating is minimised. Pretty minimal effect in any event I would have thought.


       - Andy.

     




    It's really a little more complicated than that. The order does not necessarily have to be "largest to smallest" - it's important to note that, because of the thermal protective element, breakers, mcb's and RCBOs, just like fuses, get hot. If you have two breakers adjacent with high duty cycle, they may overheat. Putting devices with a low duty cycle (lightly or infrequently loaded circuit) between devices with a high duty cycle (heavily loaded and/or frequently loaded circuit) is the guidance given by most manufacturers of DBOs and CUs.

  • 0

    mapj1:




    I think this is the politicians use of the word "minimise" of the inconvenience, meaning 'not make it overly big' rather than the engineering one where we really mean 'make it as small as is possible'




    I prefer to make an installation as safe as is possible, staggering circuits across RCD's is commonsense to achieve this, is paramount IMO. Further, where a vulnerable person is involved, I do suggest a scatter of emergency light fittings, e.g. "now where is that toilet roll?".  I would like to see this provision of emergency lighting for vulnerable persons, made obligatory by local authorities and in the regulations for suchlike.


    Jaymack.
  • 0

    AncientMariner:




    davezawadi:

    ..... A quick swap around of a couple of MCB's would fix it anyway. 



    Is there a requirement for MCBs to have reducing ratings working away from the RCD? ie, in reverse order: 40, 32 , 32......16,..6, 6  Or just common practice?

    Clive

     




    Just sensible common practice I believe, so that heavy currents travel through the shortest most direct bus bar route.


    Z.

  • 0
    Picking up on what Graham said above, I have installed economy seven consumer units with alternate ways left empty to allow the MCBs to run cooler.


    However there’s no specific regulations regarding the ordering of devices in a consumer unit, it’s just convention to put the largest protective device next to the main switch and number them from the main switch, even if the main switch is on the right so the numbering is backwards.


    Electricians are stuck in their ways.


    Andy Betteridge
  • 0

    AncientMariner:


    Is there a requirement for MCBs to have reducing ratings working away from the RCD? ie, in reverse order: 40, 32 , 32......16,..6, 6  Or just common practice?

    There is the argument of having the heaviest currents flowing through the shortest length of the busbar, but this is also dependent upon the amount of current consumed by each circuit which can vary. Current density will always be highest at the supply end of the busbar regardless of the ordering of the MCBs.


    Another argument is having the MCB for the lighting circuit in the room of the CU at the far end so you can easily feel its position when it trips during the hours of darkness.
  • 0

    I prefer to make an installation as safe as is possible, staggering circuits across RCD's is commonsense to achieve this, is paramount IMO.



    In which case twin RCD CUs are out - all RCBOs would be the only option.

       - Andy.

Community Rules & Guidelines