18th Edition Consumer Units / Distribution Boards

Question

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?

mapj1 · Accepted Answer

Get your tame electrician to agree this, but the prohibition on plastic consumer units is to prevent fires inside domestic property. You may sensibly argue that if it is an a location which even if it burst into flames, the house would not be affected, that a plastic unit is perfectly safe. Personally I have a couple in damp garden-shed like places where a steel unit would be asking for trouble in terms of corrosion. - there are times when one has to be a bit pragmatic, and these are very reasons the plastic ones are still made and sold. 
 It is also possible to supply an outbuilding without a local dis board at all, as one circuit if the power demand is low, and a socket radial can have a fused spur as the light switch. 
 Also consider where RCD protection is, and how easy to reset if it pops off leaving you in the dark in the garage. 
 Mike.

18th Edition Consumer Units / Distribution Boards

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