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Distribution circuit protection ..


Danny

Question

Does a distribution circuit need RCD protection .. ?

I've got a client who is happy to shell out a few bob on power for garage and summerhouse so i've suggested the following ..

New 20A MCB D/Circuit on main switch side of existing split load board to garage CU .. main switch, 16A RCBO sockets, 6A RCBO lights, 20A MCB onward D/Circuit to summerhouse .. main switch, 16A RCBO sockets, 6A RCBO lights ...

You'll see that the emphasis is on convenience in the case of tripping .. but as the D/Circuit is effectively supplying fixed equipment does it need RCD protection and if so that's the convenience aspect effectively out of the window ..

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7 answers to this question

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Evans Electric

I would not think so , as long as its fixed surface .

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hi there,

Cable in wall/depth reg still applies, unless its protected.....

The only difference for a distribution circuit is 5 second disconnection time.

O.

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I assume you are putting RCD's in the garage and summer house? If so then you do not want standard 30mA RCD's at the supply end of the Distribution Circuit as it will not have discrimination against the ones at the other end. Same goes for MCB sizes as a 20A may still trip when a 16A does (or ass close to it) so you may want to upgrade those MCB's and cable sizes.

Ian.

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PC Electrics

Does a distribution circuit need RCD protection .. ?

Not per se, no. The usual requirements for cable protection apply though, so if it were t&e buried in plaster then an RCD would be required. Since you want the RCDs at the usage end, use swa for the d/c or route on the surface.

New 20A MCB D/Circuit on main switch side of existing split load board to garage CU .. main switch, 16A RCBO sockets, 6A RCBO lights, 20A MCB onward D/Circuit to summerhouse .. main switch, 16A RCBO sockets, 6A RCBO lights ...

The 20A MCB in the garage for the d/c to the summerhouse does not provide discrimination with the 20A MCB at the house and is thus redundant. You could either:

1) simply "loop" the feed through the input side of the garage main switch so that the entire d/c cable run is protected by the MCB at the house, saving you one MCB at the garage. Or,

2) use a 16A MCB or RCBO in the garage for the d/c to the summerhouse, then simply connect this direct into the sockets in the summerhouse and use an FCU (RCD-FCU if needed) for the summerhouse lights. You could use RCD sockets if only one or two, or run through an RCD in a small 2 way enclosure if more. Depends whether you need RCD protection for the summerhouse lights and whether you're bothered about keeping them separate in that building. This method can save you a mini CU and 2 RCBOs. Or,

3) Up the MCB at the house to 32A to provide discrimination.

You don't state the power requirements for each building, but assuming the consumption is likely to be light I suggest that 2) above is likely to be the most cost effective.

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