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18th Edition Consumer Units / Distribution Boards

John Ford

I am extending an existing electrcial circuit in my house to a shed and garden. A registered electrician will be completing the work but I am tasked with buying the materials. The circuit will be fed from the existing house distribution board to an additional distribution board to feed the shed and garden sockets. The additional distribution board will be outside as a temporary measure until I build a brick garage at which point a permanent installation will be made and the distribution board moved inside. I believe the minimum I need for a board located outside is IP44, I am unable to find a metal unit with an IP44 or higher rating, they are all plastic. The oustide distribution board will have an isolator switch and an MCB to protect the shed/garden circuits. My question is do the current regs require all distribution boards to be metal or do they allow plastic when it is a downstream of the main house board or outside? Any other thoughts / input gratefully received?

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    The CU/DB (consumer Unit / Distribution Board) should use Main Switch & RCBO and not MCB.  Consider the cable from the house to the shed.  SWA (Steel Wire Armoured) is normally used, worth considering using something like Docaster EV ultra it can deliver power a data via cat 6 in one neat bundle to the shed.  Use it for WiFi.

    Depth of cable if buried at least 500mm below glound will add 1 meter of length to your cable.  Then do cable calculation with volt drop to confirm.  To be honest this is the role of the designer which will probably be your electrician. 

  • 0 in reply to Sergio Fernandez

    "The CU/DB (consumer Unit / Distribution Board) should use Main Switch & RCBO and not MCB. "

    It certainly could - I think to say should which implies must is a bit strong, certainly there should be RCD/RCBO protection somewhere, but that could be at the house supply end.
    It rather depends what is going in the garage eventually, if for example it really needs separated power and lights circuits, or if it needs data cable as you suggest for that matter - it is nearly twice the price of the normal SWA of the same capacity.

    What you describe may be a bit more gold plate than is needed.

    Also if there is any chance in the future that there may be an EV charger or a service that needs bonding (like a water pipe) then the decision to export the house earth or to make a TT island needs to be made, as indeed the total load and the distance will determine the cable size in the normal way.

    Mike.

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  • 0 in reply to Sergio Fernandez

    "The CU/DB (consumer Unit / Distribution Board) should use Main Switch & RCBO and not MCB. "

    It certainly could - I think to say should which implies must is a bit strong, certainly there should be RCD/RCBO protection somewhere, but that could be at the house supply end.
    It rather depends what is going in the garage eventually, if for example it really needs separated power and lights circuits, or if it needs data cable as you suggest for that matter - it is nearly twice the price of the normal SWA of the same capacity.

    What you describe may be a bit more gold plate than is needed.

    Also if there is any chance in the future that there may be an EV charger or a service that needs bonding (like a water pipe) then the decision to export the house earth or to make a TT island needs to be made, as indeed the total load and the distance will determine the cable size in the normal way.

    Mike.

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