Discuss Radial or RFC for Summer house in the Electrical Forum area at ElectriciansForums.net

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Hi. I will soon be wiring up my summer house. My plan is to run 10mm2 SWA from spare 50A breaker on my house consumer unit (approx 20m) to a 40A garage consumer unit with 6A MCB for 1.5mm2 lighting circuit and 32A for 2.5mm2 RFC. I plan to have 5 double sockets which will have heater, TV and console, Bluetooth speaker, phone chargers etc and the occasional lawnmower plugged in.
My question is are my plans ok or would I be better with a radial circuit?
 

pc1966

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Plan sounds fine to me.

If your cable route is more or less a loop round the building then might as well make it RFC and use 2.5mm

If the sockets are all at the far end or no sane means of completing a loop then you might argue for a radial in 4mm (though if thermally insulated 4mm is not up to 32A so you might need to derate to 25A MCB).
 

timhoward

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Nothing wrong with plan.
My personal preference is to split tails in house and use fuse to protect SWA.
Then summer house fault doesn’t trip RCD in house and summer house has local RCD.
But it’s a nice to have not a must have.
 
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littlespark

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If the rcd in the summerhouse is only rated to 40A, then downgrade the house 50A to less than or equal to 40. Or upgrade the rcd to 63A

An 40A RCD doesn’t trip off at 40A, that’s just what it’s been tested to handle.
It’s like a light switch, rated at 10A still has a 6A breaker protecting it.
 

pc1966

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Thanks. Sorry I meant I plan to use twin and earth cable, I didn’t make that clear.
If using T&E then a couple of points you should take care over:
  • It is not suitable for burial. I am sure you already knew that, but I have seen it done :(
  • It is not UV rated, so if routed outdoors it should be in some form of conduit/trunking/etc to keep the sun off it (less of an issue in Scotland and/or north facing admittedly, but still the regs demand it for good reason).
  • If the route has the cable hidden from view and less than 50mm from any surface it has to be 30mA RCD protected as the supply end (in case someone nails it in the future, etc. I guess they assume few folk use screws/nails over 50mm!).
 

nicebutdim

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Just some guesses...

OP states SWA, but doesn't mention of number of cores.

Buzz mentions 3 core, rather than 2 - possibly misread "mm2".

OP's subsequent mention of T&E refers to circuits from sub board.

Hopefully the above are correct as I can't see how sub main could possibly change from SWA to T&E in a few short posts..
 
OP
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Thanks again folks, sorry for not being clear.
Plan is 10mm 3 core SWA from house CU to summer house CU, buried underground where it runs outside. 2.5mm T&E for RFC inside summer house and 1.5 mm T&E for lighting, also inside. 30mA RCD in summer house CU.
 

pc1966

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Plan is 10mm 3 core SWA from house CU to summer house CU, buried underground where it runs outside. 2.5mm T&E for RFC inside summer house and 1.5 mm T&E for lighting, also inside. 30mA RCD in summer house CU.
Sounds fine.

Depending on what you have or need to buy, it might be cheaper just to wire the lights in 2.5mm as well, also note that lights can be in 1mm which is easier to wrangle in to some LED fittings.

Screwfix sell Prysmian cable in smaller quantities, a good brand:
 

pc1966

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One final point of note is to use decent glands for your SWA cable, and to have a flying lead for making sure it is properly bonded to the earth.

If affordable, I would use this sort of thing:

Yes, they are outdoor rated which probably you don't need, but do a really good job at clamping the cable. They also come with the "earthing nuts" that have a grub screw to lock them in place, and a tapped hole & screw for a ring terminal to add the flying earth lead. However, you can use the conventional ones with the "banjo" earth tag, or even just get the earthing nuts / piranha nuts separately.

However, double-check that is the right size for your cable!
 
OP
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One final point of note is to use decent glands for your SWA cable, and to have a flying lead for making sure it is properly bonded to the earth.

If affordable, I would use this sort of thing:

Yes, they are outdoor rated which probably you don't need, but do a really good job at clamping the cable. They also come with the "earthing nuts" that have a grub screw to lock them in place, and a tapped hole & screw for a ring terminal to add the flying earth lead. However, you can use the conventional ones with the "banjo" earth tag, or even just get the earthing nuts / piranha nuts separately.

However, double-check that is the right size for your cable!
Thanks again. Quality glands are one subject I am familiar with as I work in hazardous areas with Compex requirements. Appreciate the recommendation, i have mostly used Hawke but like the look of the earthing nuts you mentioned.
 

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