Summer House Wiring

[Markyuk5]

I want to add a couple of sockets in the garden - one in a pergola area and the other in a summerhouse. Both relatively low draw, although I suspect we may use a 1kw heater for short periods of times in the summerhouse.

I was hoping to make use of an external socket / fused spur which is already outside the house, rather than having to pull more wires through the external house wall.

It's an odd (I think wrong) setup at the moment - I think both existing sockets should be off the fused spur.

I was proposing to feed the new sockets from the fused spur - is this ok?

Given the total runs (approx 26m to garden socket and 65m to summer house) I take it 2.5mm SWA won't be sufficient?

Thanks!

 

[flameport]

They can all be connected to the 13A fuse, provided you don't want more than 13A in total for the additional sockets.

2.5mm² will be too small for volt drop over that distance, 4mm² is likely to be acceptable.

Does the existing circuit have an RCD, and if so, what type is it?

 

[JohnW2]

They can all be connected to the 13A fuse, provided you don't want more than 13A in total for the additional sockets. 2.5mm² will be too small for volt drop over that distance, 4mm² is likely to be acceptable.

If if that full 13A were drawn, the VD over 65m of 2.5 mm cable would only be about 15.2V (about 6..6%) which would be most unlikely to upset any load. More to the point, if the OP's stated requirements remain as they are now (about 1kW maximum load), that would only have a VD of just over 5V (about 2.2%).

There's absolutely nothing wrong (within reason!) with 'future proofing', but if the OP wanted to do that, he would obviously be advised to move away from the feed through an FCU.

Kind Regards, John

 

[Markyuk5]

Thanks both for quick responses.

Current RCD is Type A.

It's very unlikely that the separate sockets would be in use at the same time (apart from the CCTV one) so I can't see it going over 13A.

Edit - actually thinking about it I may add a couple of lights in both pergola area and summer house, will need to recalc but still doubt it'd go over 13A.

One other question - can 2 core SWA be used with the shielding as earth or need to go 3 core?

 

[Taylortwocities]

Thanks both for quick responses.

Current RCD is Type A.

It's very unlikely that the separate sockets would be in use at the same time (apart from the CCTV one) so I can't see it going over 13A.

Edit - actually thinking about it I may add a couple of lights in both pergola area and summer house, will need to recalc but still doubt it'd go over 13A.

One other question - can 2 core SWA be used with the shielding as earth or need to go 3 core?

Your lighting will (I assume) be LED so the load will be relatively small. So no worries there.

For SWA, the armour must be earthed. That’s what electrically protects the cable.
If you aren’t familiar with SWA glanding then I would suggest 3-core.

@flameport has an excellent guide to this!

Steel Wire Armoured cable

Steel wire armoured cable including how to strip and prepare the ends and installation of a brass CW gland

flameport.com

 

[ericmark]

At 13 amp for sockets (5% volt drop) 4 mm² is good for around 90 meters, for lights (3% volt drop) 54 meters, as to if the volt drop is that important with LED lighting not so sure, with fluorescent using magnetic ballast and with refrigeration with non inverter controlled motors volt drop was important, but today not so much a problem.

Supplies outside more of a problem protecting against loss of PEN and in the summer house that is not really a problem.

Where I live in Wales the garden is a special location, so work needs notifying to LABC, I think the requirement was dropped in England so you are OK in London, but there was a reason why it was a special location, so care is required.

 

[JohnW2]

For SWA, the armour must be earthed. That’s what electrically protects the cable.

Indeed so.

If you aren’t familiar with SWA glanding then I would suggest 3-core.

I'm not sure I understand that. Are you suggesting that, if the OP is not familiar with 'SWA glanding', then he might terminate the SWA without using glands - but if he did that, how are you suggesting he would/could/should (satisfactorily) earth the armour?

As you are aware, opinions are quite polarised as to whether or not one should rely on SWA armour as the only 'earth'. For what it's worth, II personally tend to favour having an 'earth' core (i.e. using 3-core in the OP case) - but that's for reasons other than familiarity with (or use of) SWA glands.

Kind Regards, John

 

[Taylortwocities]

For what it's worth, II personally tend to favour having an 'earth' core (i.e. using 3-core in the OP case) - but that's for reasons other than familiarity with (or use of) SWA glands.

Was making that point in a clumsier way.
relying on the armour for an earth is fine, providing it is glanded properly, tested to ensure it meets regs.
Given the lengths proposed and (I judge) the OP’s apparent lack of expertise I too would encourage 3 core SWA.

 

[JohnW2]

At 13 amp for sockets (5% volt drop) 4 mm² is good for around 90 meters, for lights (3% volt drop) 54 meters, as to if the volt drop is that important with LED lighting not so sure, with fluorescent using magnetic ballast and with refrigeration with non inverter controlled motors volt drop was important, but today not so much a problem.

Particularly given the OP's modest requirements (which do not include any fluorescent lights or refrigeration), as I always say, I personally don't think one needs to be very concerned about the ("5%" and "3%") guidelines in an Appendix of BS7671. If one is concerned about actual regulations, the only requirement is that the voltage at the terminals of current-using equipment "shall be such as not to impair the safe functioning of that equipment" (and I struggle to think of any equipment whose 'safe functioning' would be impaired by a low supply voltage).

As I always say, let's face it these (5% and 3%) guidelines fade into relative insignificance in comparison with the range of permitted supplyt voltages. An installation normally at the top of that permitted range (253V) has to fall by 10% (of nominal) to even get down to the nominal voltage and by 16% (of nominal) before it got below the minimum permitted supply voltage

Kind Regards, John