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Primus1
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17-06-2020, 11:50 AM
1

Another question for judd

Having had my main fuse in the house upgraded, my garage is now on its own separate fuse, I’m thinking of upgrading my garage electrics, it’s been wired in swa cable to the garage terminating in a 13a fcu, I’m thinking of rewiring and fitting a garage consumer unit, ( blanking off the fcu and extending the cable to feed the consumer unit), I will be using either a two or three way unit, however, looking at the rcd on the consumer unit, it 63a, as I’m thinking of a radial circuit using 2.5 cable, for the sockets, surely this is too big?, should it not be 16/20a., ?or is this the rated breaker for the radial supply, and not the rcd..,.
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17-06-2020, 02:18 PM
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Re: Another question for judd

Is that RCD protecting the whole consumer unit and used as the main switch or just the circuit to the garage? If it's the former, it should be okay because each circuit will (Should have), its own MCB. If it's the latter, (I'm assuming that it's an RCCBO type (combined MCB and RCD)) it is far too large for a 2.5mm cable as the short-circuit current required to trip an MCB of that size would be 315Amps and would damage the cable.
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17-06-2020, 03:19 PM
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Re: Another question for judd

I'd agree with Judd on this, the absolute maximum a 2.5mm cable can carry is 27Amps, so in general depending on the governing factors, such as length of run, loop impedance etc the maximum breaker you want to be using is a 20 Amp type. I too have the feeling that the RCD is probably protecting the whole board rather than individual circuits, although to be honest, if the board was replaced under the 18th edition regs then it should be a split load board, in other words 2 RCD devices. unless you can get a feed from the house consumer unit that is not RCD protected you need to be mindful that even if you fit a consumer unit in the garage with it's own RCD you may find the one in the house will trip in the eent of a fault as you will have two, 30 milliamp RCD's on the same circuit and as such won't get discrimination for fault protection.
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17-06-2020, 06:21 PM
4

Re: Another question for judd

Yes it’s a split load board with 2 rcds, so do you reckon it’s not worth fitting a consumer unit in the garage, and just leave as is, ?
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17-06-2020, 06:46 PM
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Re: Another question for judd

Is the armoured cable at both ends made off into the proper SWA glands? What size is the cable? Personally, I'd get rid of the FCU in the garage and replace it with a galvanised steel conduit through-box and extend the wiring from there to a new `garage` style consumer unit. No need for an RCD in the garage unit as it is protected at the mains end by an RCD. I would feed the SWA cable with a 20amp MCB (depending on size of cable) and put 10A & 6A MCBs in the garage unit to split the load.
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17-06-2020, 09:57 PM
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Re: Another question for judd

Well, the swa to the garage starts as I think 4mm from the fuse box to a metal box in the attic, swa then runs from that to the garage, it was like that when we moved in some 30 years ago,
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18-06-2020, 11:56 AM
7

Re: Another question for judd

Originally Posted by Judd ->
Is the armoured cable at both ends made off into the proper SWA glands? What size is the cable? Personally, I'd get rid of the FCU in the garage and replace it with a galvanised steel conduit through-box and extend the wiring from there to a new `garage` style consumer unit. No need for an RCD in the garage unit as it is protected at the mains end by an RCD. I would feed the SWA cable with a 20amp MCB (depending on size of cable) and put 10A & 6A MCBs in the garage unit to split the load.
I agree with you on this, the fcu definately needs to go, the only thing I would do different is use a galv adaptable box to extend the cables with rather than a through box, it may be ok for me and you doing it that way being sparks, but you know how much of a cow it can be getting a decent joing in such a small space, for a diy'er a box would make it a lot easier.
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18-06-2020, 05:35 PM
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Re: Another question for judd

Originally Posted by Primus1 ->
Well, the swa to the garage starts as I think 4mm from the fuse box to a metal box in the attic, swa then runs from that to the garage, it was like that when we moved in some 30 years ago,
Can you get to the metal box in the attic to check on the SWA to see if it's terminated properly, whether it's a 3-core cable supplying the garage and if there's a proper earth connection? Determining the SWA cable size would be handy too to see how much load it can take and to calculate the volt drop.
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18-06-2020, 07:12 PM
9

Re: Another question for judd

Originally Posted by Judd ->
Can you get to the metal box in the attic to check on the SWA to see if it's terminated properly, whether it's a 3-core cable supplying the garage and if there's a proper earth connection? Determining the SWA cable size would be handy too to see how much load it can take and to calculate the volt drop.
Will have a try judd, especially as the electrician tested the garage circuit and said the readings were a little high, ( but within tolerances)
 

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