Hi Guys, Need advice on power supply to outbuilding which I'm planning to build shortly before building an extension and loft conversion on main house (inc full re-wire.) How do I go about calculating what I will need in terms of cable size and presumably a small secondary consumer unit? what about earth? The building will be around 30m from house, 40m from consumer unit. We would like to 'camp' in the outbuilding so we are out of the house and still onsite for the build which will mean a toilet and maybe some kind of water heating (presuming any domestic electric shower is a no go - maybe a 2kw water heater - not expecting anything other than a trickle for a shower) plus 1 or 2 electric heaters. And of course lighting and sockets. Outbuilding will be timber frame, fully insulated (50mm celotex floor, 50mm celotex +100mm rockwool walls & ceiling) and just under 30sqm footprint. I'll be digging a trench to connect to mains drainage and will dig a smaller trench within this to 750mm+ for a water pipe below frost level. somewhere above this in the trench will go a power cable and outdoor cat6 (recommended distances?) From a quick search cable cost for 40m is; 10mm - £3pm = £120 16mm - £5pm = £200 25mm - £7pm = £280 So in my eyes, thats no big deal just get what I need. As I said, temporary living accommodation, anti-frost heating, a small water heater if possible and then in the future, maybe a carpentry workshop or maybe a man cave with guest accommodation. We have planning approved, building control appointed and an electrician lined up but I'm a belt and braces kind of guy and would like to cover this myself. Any advice welcome! Let me know if you need a list of appliances that might be used?
Can you not liaise with the electrician Part? He will do all appropriate calculations and then come up with a cable csa. Under the sparks supervion you will be able to dig the trench etc etc, and then put cable in said, and then after the sparks approves you will be able to back fill etc..also you can drill holes through wall and stuff.
Attached is the planned trench, but my questions are more around whats needed on the electrical side. how is it calculated as for load / losses for distance etc and has anyone had experience with heating and water heating for outbuildings. cheers
The load/cable calcs should be done by your electrician. As said above, he/she will have to CERTIFY that he/she has done the DESIGN, TESTING and INSTALLATION of the electrics.
I have multiple outbuildings at my house and the supply was installed to a small outbuilding before the house was built. My solution was to run a ring in 16mm SWA with isolators on each leg to CCU's at strategic points. It works very well, little VD and very reliable. 16mm SWA to your temporary home should be large enough, fit a small electric shower and some heating, a 60A breaker on the 16mm supply will protect the cable adequately.
You can get an idea on cable size using this tool https://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html but your Spark will need to confirm. Best engage a spark at the outset and work with him.
Have a look at SIPs. You can but them online and they seem a great way of building an insulated timber frame building. I'm plotting and scheming one at the moment. https://www.sipsdirect.co.uk/
Yep I've got a sparks, he's starting on the house in a couple of weeks after a holiday. just wanted to get an idea myself of what would be needed. Don't want to bother a 2nd sparky for a quote as I know who I will be using. I'll get him to do all the calcs. Just wondered if there some general rule of thumb for consumption, distance and what I need to consider when listing my requirements. As you all says its all under planning and B/C so will be done properly. Just trying to get ahead of the game and price it all up.