# Chalet power supply from main house

Hi Guys, I live on a farm that my grandparents used to live on, they had a summer house/chalet that they used to live in in the summer whilst they letted out the main house. They used to power the chalet with a diesel generator but now I want to know how difficult it would be to put mains in from the main house. I measured the distance a potential cable would have to go, and its about 100 metres. Ideally it would come off the consumer unit of the main house but I'm not sure if this is possible which is why I'm looking for some advice! The cable would go in the ground in some ducting, would be single phase, and would be standard uk 240v (or whatever it is +-5v????). Ive read a bit about voltage drop but I'm not sure what this means, also I've read somewhere that I'd have to calculate the potential load. It has two small bedrooms, a bathroom and a kitchen/diner/living room. Do I just list every appliance in there and add them all up to determine the cable size? Any info would be very much appreciated!!! Many thanks
Masterofnone
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At 32A using 16mm SWA the volt drop for 95 meters is 8 volts. You are permitted maximum for lights 6.9 volts and sockets 11.5 volts so although not really within the limits it would likely be good enough.

So your looking at £500 for cable.

If you can run on less than 32A for example 16A as used in a caravan the you could install thinner cable. If you use all HF fluorescents or LED lighting although not complying it will likely work many LED's will work 150 ~ 250 volt AC.

Fridge/freezer can be a problem but again using inverter types these will work with more of a volt drop.

But at £500 for inverter fridge/freezer may be better buying the cable. My quick calculator was only designed for up to 16mm go to 25mm and then looking at £800 for the cable.

In the grand scheme of things a £1000 may work out cheaper than buying replacement generators every few years by time trench dug etc of course the price can go well above that and could end up more expensive than having a dedicated supply.
ericmark
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Thanks for the reply!! I decided to buy a 25mm cable to be on the safe size. done some calcs online and at approx 100m 25mm2 is good for 60amps which i know will be plenty for me! Next question ha! Should i use a circuit breaker at the house end and if so i assume a 60amp one would be ok for this? Also what is the difference between a circuit breaker and an rcbo or are they the same?thanks again
Masterofnone
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To keep within the volt drop limits for lights maximum current is around 45 amp for power around 73 amps to keep within the 3% (6.9 volt) and 5% (11.5 volt) however in the main the house is supplied well within the -6 ~ +10% of 230 volt and 0 ~ +10% is common so you can normally afford to have a larger than permitted volt drop. Using LED lighting then even with a 20% volt drop there is likely no problem.

So names
An automatic miniature circuit breaker (MCB) which typically will range from 4 amp to 70 amp and then a moulded breaker which are much larger and go from 30 to 500 amp. In both cases you can get units which add to them and make them into a RCBO which is a MCB and RCB combined. With a moulded breaker the current transformer and the control panel are separate and feed into the moulded breaker also they are user settable so not permitted for use by ordinary persons.

You also have an isolator which is a switch.

And of course a fuse.

So the first point is to find out size of MCB which will fit in your board. Many boards are limited to 45A and you have to decide if that is the case do you want to limit to 45A. With a standard house you can have 60, 80 or 100A DNO fuse but with a farm you may have split phase or three phase and it could have a larger than 100A supply. But a standard consumer unit is limited to 100A so using 45A to supply the second building would seem sensible.

This is not a DIY job giving you info to help to decide what is feasible is one thing but using Henley blocks to split the supply means drawing the DNO fuse and it would be illegal to DIY this work.

If it were my job I would likely use a 160 amp three phase switched fuse box to split the supply and 60A fuse for house and 60A fuse for out building. Also I would have to give a lot of consideration to earth system used possible it would be TT. However until I visited the site I would not know which way to go. It needs an electrician it’s not a DIY job.
ericmark
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Joined: Fri Oct 02, 2009 8:49 pm
Location: Mold, North Wales.

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