My house has an electricity point about halfway down the garden that a previous owner used for his pond equipment which is no longer used but works OK.
The supply is underground, I dont know how deep ,and is in an armoured cable about half an inch thick.
I would like to extend the cable about 50 yards to a proposed summerhouse.
The questions are, does it have to be underground ?. I could run it along an internal fence . If so so how deep ?. What sort of cable should be used.
It will probable be used for an electric kettle and lights.
No. However, if it is, it needs to be deep enough to be unlikely to be disturbed by whatever happens above, such as digging over the vegetable patch. 450mm is often used as a guide. Should have marker tape buried but spaced above it too.
SWA (which is probably what existing is) would be best. In some circumstances you might be able to use a lesser spec'ed cable.
Now the difficult bit - what load, and is the cable beefy enough for the length and load involved, and what sort of protection and earthing, etc.
We'd need to know what size and length the current cable is, how the circuit is currently protected, what extra length needs to be added.
This comes under Part P notification too. Given the nature of your questions, it might simply be worth getting an electrician to quote for doing it. There are particular issues with outdoor electric safety, and circuit protection for long cable runs which could bite you (although I'm sorry to say, they'll confuse some electricians too). You might offer to dig the trench if undergrounding it.
Do you know how many cores? (i.e. anything written on the side of it, or have you opened the box it connects to?)
No, it can be elsewhere. One is not supposed to fix "permanent" cables to temporary stuctures like a fence, however clipped along the gravel boards (if fitted) would probably work out ok in reality.
SWA
formatting link
you know the number of cores, the above will probably let you work out the spec of the cable from the measurements.
There is a fair chance its the smallest size available - i.e. 1.5mm^2 conductors.
We need to know where it is fed from the house end of things... e.g. another circuit, dedicated way at the CU etc.
How long is the existing cable?
Sounds like a total load of 16A would be adequate. Chances are the cable you have is up to it in terms of current carrying capacity, however other issues like excess voltage drop could prove more problematical.
While certainly doable, its worth noting that designing outside supplies etc is a non trivial exercise, and there is a fair amount to consider. Some of the basics are covered here:
The Wiring regs (reg 522, specifically) effectively don't allow the installation of fixed cable to an unsound structure (although they don't say this in so many words). Fencing counts as an unsound structure.
Section 708 which regulates the commercial side of what you're proposing (electrical installations in caravan/camping parks) only allows for overhead or underground cabling, with underground being the preferred option.
Trench in a new SWA cable. Probably 10.0mm SWA @ 100yds @ 13A kettle etc. Due to the distance it would most likely need to be TT supply.
Your problem is really the distance - 50yds is a long way, 100yds is a very long way.
You can shrink the size of SWA required.
17th imposes 3% voltage drop on lighting, 5% on power. An electrician may argue you do not need to comply with the 3% on lighting in what is likely to be occasional leisure usage in a summer house and so merely comply with the 5% requirement for power noting it as a (minor) departure from BS7671. Relaxing the voltage drop requirements means you can use a smaller cable - but 100yds of SWA in any size is not going to be cheap.
You can run SWA on the surface if it is reasonably protected, but not on a fence. The SWA needs to be at a suitable depth for the usage of the ground, which may be 450mm if normal usage or deeper if you are running through cultivated ground, then 150mm coverage of sand and cable marking tape.
So it comes down to SWA cost + trench digging effort.
Per cup of tea or coffee made at the other end it is not going to be cheap :-)
When the quote arrives 99.9% will buy a long extension cable and use that due to the high cost of getting an electrician to do it.
The lights will dim when the kettle goes on but does it actually matter? There will be less heat per meter of cable so it isn't going to overload.
Of course there is the even more dangerous method of getting a kettle there and that is a primus stove.
You can buy lower wattage kettles intended for caravans, etc. which are only about 700-1000 watts which reduce the voltage drop a lot making extending the existing cable OK, probably.
- 100m of 2x 50m 13A extension reels - =A365 delivered.
- 100m of 2.5mm Arctic - =A377 delivered.
- 100m of 2.5mm H07RNF - =A395 delivered.
- 100m of 2.5mm SWA - =A3130 delivered.
- 100m of 10mm SWA - =A3320 delivered. Not happening :-)
Most likely solution is 1x 50m 13A extension reel (=A333) into the halfway socket.
A kettle is a periodic load. Welders often run 50-90m off a BS4343 adapted cooker supply, considering there is on right-angle BS4343 plug that must be one hilarious "wall ornament" they have there in the middle of a domestic kitchen :-)
Whatever solution the OP chooses, make sure there is a working RCD.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.