Shed Electrics

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On Mon, 19 Jan 2004 15:08:13 -0000, "Christian McArdle"

As per the regs then?

From the fixed wiring in the shed.

Kind of true, actually entirely true, however the regs don't allow you to do this.

That is assuming there is a suppliers earth and it is all correctly connected to the installation.

I personally favour an RCD at the house to cover the cable also in the event of a spde related incident or similar!

As you say, a prebuilt 'garage unit' with 30mA RCD, 16A and 6A MCB in one pvc enclosure would be the cheapest solution.

SJW A.C.S. Ltd.
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Regarding the earth.
So, you take the cable from the house csu to the shed and do you connect the earth to the shed csu or direct to the earthing rod.
The which? book doesn't make this clear and actualy says not to connect the house>shed cable earth wire to the shed csu, connect the shed csu to an earth rod, but what would you do with the house>shed earth?
It's probably obvious to you all but not to me.

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The cable you use as the supply should be connected at both ends regardless. The only thing you need then is to connect the earth bar in the consumer unit to an earth rod in the ground local to the shed. The requirement is not to rely on the length of cable your using as the supply as the main earthing point of the shed, because if this breaks down in any way it is not supplying a proper earth point to the shed.

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How deep should I go, I heard 2m but that seems a lot for 2 or 3 double sockets and 1 or 2 lights.
Also what, in your opinion, supply cable mm2 size should I use 4 or 6mm2? Should a 4mm2 use 30/32A and 6mm2 use 40A. Plus what earth cable to rod should i use?
Many thnx

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On Mon, 19 Jan 2004 15:28:34 +0000, Matt Pearson wrote:

What value do you put on your life ?
Dave
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If you go with a 6mm csa' SWA cable with a 40amps breaker in the house, then you can literally fit and forget it, because it is heavy enough to take any sort of load you put on, within reason of course, and the difference in the price between 2core X 4mm and 2core X 6mm isn't that much for a more safety conscious supply that is going to last for many, many years.
The earthing cable between the CU and the rod should be taken in 16mm which is the heaviest needed by any installation and introduces the least impedance (resistance) to any fault current. This 16mm cable combined with a 2mtr length of copper pipe hammered into the ground, and a proper earthing strap wrapped around it, is going to give you a very safe supply which will keep its integrity through many a large fault condition if it needs to. What you want from a local earthing point is that the impedance is as low as possible between the consumer unit and the ground. So taking 2mtrs of copper into the ground is about the right amount to keep good contact between rod and ground in almost all conditions.
The consumer unit should also have an RCD main switch fitted which will drop the supply at the slightest hint of a local fault in the outbuilding without causing nuisance tripping back at the house.

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many thnx for your advice, it's all clearer now

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Matt Pearson wrote:

2m is likely to be excessive. The recommendations say at least 450mm but more if it is likely to be heavily dug over - say 800mm.
Normal practice is to bury the cable - back fill 150mm or so, and then lay a warning tape, then backfill the rest. That way if someone does get carried away recreating their very own air raid shelter in the future they should reach the tape before they get chance to damage the cable.
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John.

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in sand
- back fill 150mm or so, and then

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