[Jukes Mum]

Not sure if this is the correct place to ask, but I am seeking some opinions about which electric cable to buy.
It is to run from the house to a small barn at the top of the garden (100m ish).
At the moment, I only need it for a heater in the kennel (a little oil filled tube heater), but in the future I am converting one side of the barn into an office. Then it will need to run lights, a kettle, fan heater etc.
I don't want to buy something now which won't be good enough in for the future usage.
I have been advised that while ideally I should obviously use armoured cable, this is expensive and it would be fine to use a flexible cable in a conduit.
There will be no connection out doors.
The cable will have to run up the fence (as the ground is too stoney to dig the channel I was going to use).
So my questions are
1) while not 'correct', is it OK to use cable in a conduit rather than armoured cable?
2) What thickness of cable do I need?

Sorry if this sounds daft.

[henchard]

mab is the person to speak to as he is an electrician (and wired my shed up). Send him a nice PM!


But it is my understanding that all installations have to be done by an electrician these days and also  comply with building regs. I believe that if you run cable outside it needs to be mechanically protected (hence the need for armoured cable)

The voltage drop over this distance will require a fairly substantial cable. Mine needed 16mm for a 130m run.

[Fleecewife]

From Mr F:
Use armoured cable, 3 core, 4mm core diameter (for 35 amps). There is no point in skimping - to do so would end in tears. Running up a fence I would say is dodgy. In our case I got a contractor with a digger to put in a 100metre trench, 3 ft deep to connect our new studio/workshop to the house. Expensive at £200, but worth every penny.   

The cable is 100m £218.39 from Screwfix

We had Scottish Power engineers mending a power line here a few years ago - they hit an unknown, unmarked buried cable which made the most enormous bang and blacked out the area for hours (Mr F slept through it all  )

I have a very healthy respect for electricity.  We still don't really know how it works, and we don't know how to control it, so don't take chances.

[shygirl]

we have buried armoured cables going to our barn, but also have an ordinary electrical cable (inside a water pipe but under a footpath) going to a outbuilding it been no problem so far. 

[mab]

cheers John  ,


As a sparks I sort of have to say that power to a barn really should be installed by a qualified person with the right test equipment, as there are questions about the suitability of the earthing system of your installation for outdoor/livestock areas; installation and verification of earth rod(s) at the barn and whether or not the cable needs to be RCD protected or not - which cannot be answered without visiting the site and looking and testing.


if the 'barn' is essentially an indoor area with a dry nonconducting floor (e.g. suspended floorboards, not concrete on earth) and there are no 'extraneous conductive parts' like metal pipes or structural steel, and/or there's no livestock then it may not be such an issue.


As for the cable- As John says the cable needs to be mechanically protected - that doesn't have to be armoured cable but the question is how much protection your proposed conduit provides, especially if it's not buried 2 or three feet down out of harms way.


It is allowable to run a cable along a fence as it's visible and can be avoided, but you have to consider the risks of the location (tractors/lorries turning / animals chewing).


I generally find that armoured is as cheap or cheaper than the alternatives anyway (buy online - google it), and if/when the cable is breached, it's certainly safer to have a cable surrounded by an earthed steel screen than just having an extra layer of plastic (the armour of the SWA must always be earthed).


There's a useful calculator here for cable sizes you can play with:


http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html


which will tell you the cable you need to comply with building regs (3% v drop for lights and 5% for other loads IIRC) and will also tell you what the designated cables current carrying capacity is.


But if you plan to use a fan heater (2kw) and a kettle (say 2.4) and you don't want the lights to dim when the kettle / heater are turned on then I think it'll tell you you'll be wanting 16mm 3 core SWA.
If you disregard building regs and don't mind the lights dimming a bit when the kettles on you could get away with 10mm, and if you're willing to unplug the heater when boiling the kettle you might even get away with 4mm, but if someone comes along and plugs in a big compressor or something the lights may dim a lot. NB if you have a 13A socket on the end of the cable then the minimum load you should specify for the calc is 3.1 kw regardless of what you're planning on plugging in - unless you put a fuse/MCB on the upstream end of the cable to limit it to less that this.


If you are going to be naughty and do it yourself (which I don't recommend) then make sure that everything is protected by a 30mA RCD (including the cable) as a minimum precaution.


if you do go for a weedy cable and your office ends up with a fridge and a computer, you may find your computer doesn't like the voltage dips when the fridge turns on - they draw quite a surge on startup.

[Jukes Mum]

Just wrote a reply but it vanished as the picture size was too large, but it said something along the lines of..
Wow, thank you so much for your detailed reply! It has certainly given me something to thing about.
The fence is the border between our garden and the neighbours, so no chance of vehicle etc. The barn has no livestock, it is an old pig barn at the top of the garden. It will have a concrete floor.
The pic is of the fence line and you can see the small barn at the top right.