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Outbuildings - multiple consumer units

Former Community Member
Former Community Member
Evening all,


In a situation where I'm shortly going to be rewiring a new house I'm moving into and am hoping someone can provide me with some clarity on the best way to provide power to multiple outbuildings. 

Essentially I had planned to install a main consumer unit indoors and then feed the outbuilding via an RCBO on this consumer unit, i.e. consumer unit to, twin and earth, to junction box internal, to SWA across the garden, to secondary consumer unit in outbuilding - repeat this 2 or 3 times to the various outbuildings I need power in. However when doing a bit of research on the subject there seems to be differing opinions on whether to do this or to install a Henley block at the main incoming supply and then come out of that with one feed to my 'main consumer unit' and another feed out to the 'secondary outbuilding consumer unit' or multiple consumer units. It never occurred to me that this was an option and frankly I'm in a muddle as to what the consensus is on best practice, some mentioning a Switched fuse also.


If anyone could give me their opinion on what the safest and best practice is i'd be extremely grateful! TIA
  • 0
    whjohnson:

    Chris,

    If you are defining the house CU as 'the primary distribution board, how can you provide adequate discrimination via mcbs only?

    Rather, I suspect you are saying exactly what I said!


    There shouldn't really be any faults in the fixed wiring if it is done correctly and not abused.


    Tripping off all of one of a series of outbuildings isn't the end of the world. A fault in any one distribution circuit would trip its MCB as intended, but the other ones would not be affected so there is some merit in having one distribution circuit per building as suggested by the OP although I see that the proposal has changed.


  • 0
    I would only add that if you are thinking of 10mm I'd put in 16mm. You'd be amazed at how unforeseen demand creeps up and it won't cost much more. Same with your other outbuildings, go one size up at least.
  • Former Community Member
    0 Former Community Member
    Thanks for your responses all, seems like I've got a good way forward with a slightly modified plan to the one in my last posts i.e. Henley block - Fused isolator (60a) - 16mm SWA - Split consumer unit (non RCD protected MCB feeding 2nd outbuilding consumer unit and RCD section with MCBs feeding 1st outbuilding circuits) - 10mm SWA - 2nd outbuilding split consumer unit (non RCD protected MCB feeding 3rd outbuilding consumer unit and RCD section with MCBs feeding 2nd outbuilding circuits) - 10mm SWA - 3rd outbuilding regular RCD protected consumer unit 

    All outbuilding consumer units being split boards with feed to next not on RCD and circuits from that unit covered on the RCD section. 


    Not entirely sure whether I'll do all the outbuildings as TT or not, possibly TT shared across the last two and its own dedicated TT for the primary. Each SWA's armour being bonded at the previous ground, i.e. 1st bonded with the house, 2nd bonded at the 1st, 3rd bonded at the 2nd.
  • 0
    We know nothing about the various buildings, but it seems far too over-complicated. What you need is an electrician who knows about design.
  • Former Community Member
    0 Former Community Member
    Hi Chris


    What exactly do you think is complicated? It’s essentially what you suggest in the first instance of feeding a board from another board but the original supply from a Henley and fused isolator? Plus seems sensible in my mind if I can to use RCDs in each board configured to prevent the previous outbuilding tripping?
  • 0
    gbruell:

    What exactly do you think is complicated? It’s essentially what you suggest in the first instance of feeding a board from another board but the original supply from a Henley and fused isolator? Plus seems sensible in my mind if I can to use RCDs in each board configured to prevent the previous outbuilding tripping?


    The cascade of MCBs is all very well, but you probably will not get discrimination so if the last shed trips, all three MCBs will trip. At least the lights will stay on in shed 1.


    RCDs don't help in the event of a short circuit.


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