What size cable do i need?

[Mr Sparkle]

Next week I want to fit some garden lights approx 25m away from my consumer unit

What size SWA cable do I need? Is 1.5mm, 3 core suitable?

In a few years I would like to build a garden shed with power (sockets). Can I use 2.5mm 3 core cable?

 

[ericmark]

Rather a vague question, one should know what load the lights are and what load you will have in the shed, but likely answer is yes they will do the job.

 

[Mr Sparkle]

Rather a vague question, one should know what load the lights are and what load you will have in the shed, but likely answer is yes they will do the job.

Hypothetically speaking I would potentially have the following set up

2-3 outdoor floodlights (max 50w each)

10 downlights in garden shed (5W each)

Garden shed would have a toaster, kettle, microwave, iron, TV and electric heater (2x) .

What SWA cable would you suggest?

 

[ericmark]

Kettle 3kW heaters 2 x 3 kW so looking at 9 kW so around 40 amp, so bang it into my software.

So it would in theory need 10 mm² to ensure the volt drop was within the limits for the lights in the shed. Would I use 10 mm² no I would not, I would use a 32 amp MCB not 40 amp, and I would use 6 mm² cable, as in the main LED lights can stand a bit of volt drop, but rules say lighting allowed 3% volt drop, so "Hypothetically speaking" it needs 10 mm².

In fact since I don't want to pay the LABC their fee, either I would use a scheme member electrician to do it for me, or if in England would use a 13 amp FCU for the supply and cross my fingers it does not rupture the fuse. At 13 amp we get

So 2.5 mm² cable, and use a 13 amp fuse, remember to turn off heater before using kettle, since a caravan seems to work with a 16 amp supply with 2.5 mm² cable at 25 meters long, I would say 2.5² cable is ample, and the heater in the caravan could be set seem to remember starting at 750 watt and highest setting was 3 kW, and the central heating even with snow on the ground was ample on the 750 watt setting.

 

[securespark]

Garden shed would have a toaster, kettle, microwave, iron, TV and electric heater (2x) .

What SWA cable would you suggest?

Woah!

Your average garden shed does not have that kind of stuff!

Thought we were just talking a few LED lights and a socket for a lawnmower!

 

[Mr Sparkle]

Woah!

Your average garden shed does not have that kind of stuff!

Thought we were just talking a few LED lights and a socket for a lawnmower!

I was providing an exaggerated response. Like at the very most these are the sort of items I could have (like a man cave).

I would rather overspec now, knowing the cables can take whatever load I throw at it.

 

[Mr Sparkle]

Kettle 3kW heaters 2 x 3 kW so looking at 9 kW so around 40 amp, so bang it into my software.
View attachment 273197
So it would in theory need 10 mm² to ensure the volt drop was within the limits for the lights in the shed. Would I use 10 mm² no I would not, I would use a 32 amp MCB not 40 amp, and I would use 6 mm² cable, as in the main LED lights can stand a bit of volt drop, but rules say lighting allowed 3% volt drop, so "Hypothetically speaking" it needs 10 mm².

In fact since I don't want to pay the LABC their fee, either I would use a scheme member electrician to do it for me, or if in England would use a 13 amp FCU for the supply and cross my fingers it does not rupture the fuse. At 13 amp we get
View attachment 273202
So 2.5 mm² cable, and use a 13 amp fuse, remember to turn off heater before using kettle, since a caravan seems to work with a 16 amp supply with 2.5 mm² cable at 25 meters long, I would say 2.5² cable is ample, and the heater in the caravan could be set seem to remember starting at 750 watt and highest setting was 3 kW, and the central heating even with snow on the ground was ample on the 750 watt setting.

Brilliant response. Thanks again.

 

[JohnW2]

So it would in theory need 10 mm² to ensure the volt drop was within the limits for the lights in the shed ... but rules say lighting allowed 3% volt drop,...

As you know, there are no 'rules' - the 3% figure is just a guideline, so 'allowed' does not come into it. I'm sure that all incandescent bulbs, and probably most/all LED ones will work fine (with somewhat reduced light output) with voltage drops' considerably greater than 3% (although we know that you, but no-one else I'm aware of, has had problems with fluorescent tubes fed with 'low' voltage). Indeed, when I did the experiment a while ago, all of the types of LED light I had available to test worked fine (with reduced light output) at 110 V - equivalent to a 'voltage drop' in excess of 50%.

In fact since I don't want to pay the LABC their fee, either I would use a scheme member electrician to do it for me, or if in England would use a 13 amp FCU for the supply and cross my fingers it does not rupture the fuse.

I thought that outside wiring was notifiable in Wales, no matter how supplied? In any event, I suspect that the OP is probably thinking of a 'new circuit', which would still be notifiable even in England.

At 13 amp we get .... So 2.5 mm² cable, and use a 13 amp fuse, remember to turn off heater before using kettle ....

I would have thought that a 13A supply would be pushing one's luck given the long list of possible high-powered loads (including two 'heaters') that the OP mentioned. It could also probably be argued that such a setup would be non-compliant with regs, since I don't think that the designed could seriously claim that the 'design current' of the circuit (which, per regs, must be less than the rating of the OPD) was no more than 13A.

A problem with this discussion is that we almost have 'the sublime and the ridiculous'. The OP's current requirement (and, seemingly, his requirement for the next "few years"), for just the lighting, is so minimal that any available size of SWA would be adequate, but his ('future proofing') idea of what the load might be "in a few years' time" is very high for a standard outhouse. Depending on my feeling about how long that 'few years' might be, if it were me I might be inclined to now only make provision for the very modest present need, and then cross the other bridge if/when it actually does arise "in a few years' time" - after all, some of these ideas 'dreams'?) about 'the future' never actually materialise!

Kind Regards, John