Wiring to a polytunnel

The polytunnel is about 10m from the house. Because the house wall is 3ft thick, but single storey, I'm going to run the 2.5mm SWA cable, along with the water supply pipe, from the attic down the outside wall and into a tren ch; suitable protection will be used for the vertical drop.

Do I have to take the cable back to the CU or can I use an FCU and run it a s a spur off one of the house ring mains ? Particular reason for this is t hat the house CU is full !!

I'll use a 2W CU in the polytunnel for a light and a 13A socket for the hed ge cutter.

I'm looking at the TLC website and the UK DIY WIKI - am I right in thinking that TLC's 2 Part gland is what I would use for the indoor end and the 3 p art for the polytunnel end ? I've not used SWA before.

The house earthing is TT with an earth spike. The system has RCBO's and an RCD - the other out-buildings are RCD protected and with a second spike. Should I install a third spike near the polytunnel which is on the opposite side of the house from the other out-buildings, but quite close to the mai n spike?

Thanks Rob

Reply to
robgraham
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Get as much separation as you can between the two services so that "any foreseeable operation on one service will not affect the other."

While a separate circuit is preferable, a ring spur is considered OK for simple outside installations like this, with loading up to 16 A at most

- but not for anything larger. You do need to consider the total loading on the circuit though - especially if you're spurring-off in the kitchen.

A simpler solution is to terminate the SWA cable straight on to a 13 A metalclad socket, with an adjacent switched FCU (with 3 A or 5 A fuse) acting as the lightswitch.

Use BW glands for indoor situations and CW if exposed outdoors. As you may need one of each it would be cheaper just to buy a CW gland pack.

That's not essential, provided that the house earth is OK. The SWA armour will a provide perfectly adequate CPC - but a 3rd spike will do no harm. What I've done in situations like this is to drive an earth rod at each location and tie them together electrically (via the armours) to form an earth system; this will lower the overall impedance to earth and provide redundancy - if the links are broken each building still has its own rod. However if the house has any metal service pipes (water and/or gas) which are main-bonded to the main earth terminal I recommend keeping the earthing system for outbuildings separate from the house. (Ditto if the house is TN-S or TN-C-S.)

Reply to
Andy Wade

The cable ought not need much extra protection save clipping to the wall. The pipe will need insulation etc. Ideally they ought not be too close.

You can use a spur from an existing circuit if there is adequate spare capacity on the circuit, and you don't want to draw too much current. A feed for socket and light would be fine in most cases.

Since you are RCD protecting it at the head end, you don't need a full blown CU and the far end. A metal clad socket can terminate a SWA connection for example.

I tend to use external water proof sockets like these:

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To terminate the SWA on the outside, then run T&E through the wall either to the supply or to the outbuilding circuits. Saves using stiff SWA inside, and needing to bend it about too much. Also gives handy extra sockets outside.

If you buy the waterproof one you can use it for both ends, and they normally come in a pack of two.

See:

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If you are likely to do ore SWA in the future, then these are very good and make stripping down the armour easy:

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You can do either really... If all the buildings are all TT you can parallel the lot together. Alternatively you can earth the SWA armour at just one end, and keep them as islands.

Reply to
John Rumm

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Many thanks guys.

While I appreciate the reasoning behind running water and electricity suppl ies separately, that does mean two trenches which is really too much of a p ain. I'll run them either side of a reasonably wide trench under a pathway and there will be tape over the cable.

The reason that I'm coming down over the wall head (~9ft high) is that the walls are 3 ft thick and loose rubble in the middle which is awful to drill through for anything. For protection the supplies will be run down the wa ll in a wooden cover which would allow me to use T&E to an external socket and termination for the SWA.

Thanks again

Rob

Reply to
robgraham

Does not need to be two trenches - just not both down the same channel of ducting...

Yup, that sounds plausible.

Reply to
John Rumm

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