Supply a third fuse board for garden bar

[Electrical123]

Hi guys,

my brother is building a bar in his garden that is timber framed and wants some power to it.
The main board in the house has a pme earth and there a no spare ways in the board. From this board there is a 4mm t+e on a 32amp breaker off the rcd side supplying a board in a little out building about 3 metres away from the house. This out building has a 63amp main switch and a ring circuit but the circuit draws no load as the sockets aren’t used apart from a little pond pump which I’ve checked the rating off and draws about 1amp at most.

he wants power to the bar he’s building which I’m thinking off installing a garage consumer unit in, and running a 6mm swa cable from the outbuilding board(which is about 45 metres away) with a 40amp 63ma rcd main switch at the new board . The bar board will supply a few sockets, heater and lights and maybe a 13amp hot tub in future. I’ve worked out that maxium demand with everything potentially plugged will be about 27amps but it’s very unlikely the load will get this high.
My question is, would a 6mm swa on a 32amp breaker in the outbuilding board be okay to power the bar board even though the outbuilding board is only fed off a 4mm twin cable from the main board on a 32 amp breaker?

thanks

 

[marcuswareham]

Hi guys,

my brother is building a bar in his garden that is timber framed and wants some power to it.
The main board in the house has a pme earth and there a no spare ways in the board. From this board there is a 4mm t+e on a 32amp breaker off the rcd side supplying a board in a little out building about 3 metres away from the house. This out building has a 63amp main switch and a ring circuit but the circuit draws no load as the sockets aren’t used apart from a little pond pump which I’ve checked the rating off and draws about 1amp at most.

he wants power to the bar he’s building which I’m thinking off installing a garage consumer unit in, and running a 6mm swa cable from the outbuilding board(which is about 45 metres away) with a 40amp 63ma rcd main switch at the new board . The bar board will supply a few sockets, heater and lights and maybe a 13amp hot tub in future. I’ve worked out that maxium demand with everything potentially plugged will be about 27amps but it’s very unlikely the load will get this high.
My question is, would a 6mm swa on a 32amp breaker in the outbuilding board be okay to power the bar board even though the outbuilding board is only fed off a 4mm twin cable from the main board on a 32 amp breaker?

thanks

63ma do you mean 30ma

I guess it depends on the installation method of the cable as to how much current can be drawn, The garage C/U is protected by a 32a mcb so the max current which can be drawn for an extended period of time is 32a regardless of what size cable you use to supply the bar.

How long is the cable supplying the garage as you might have already clocked with the additional 45m you need to make sure the Zs is low enough to meet disconnection times and the PSCC high enough for the overload protection so this could warrant using cable with a larger CSA

Also does the construction of the garden bar lend its self to people standing on grass/soil/true earth and at the same time in contact with class 1 electrical appliances, if so some of the risks of using the PME earth down there should be considered

 

[Mike Johnson]

I think you already know the answer, 4mm T&E is rated at 32amps that is one load not two, the original supply is undersize to supply two boards.

 

[timhoward]

Will bar have lights in it? I'm additionally wondering about 3% volt drop, as I suspect the 6mm SWA for 45m won't cut it.
I'm guessing this will end up splitting tails in house, fused isolator, and 10mm SWA to bar, but that is a hunch with no calculations.