Electric to outbuildings

[Alan lewis]

I need to supply electricity to our cattery refuse. We have five cabins each of which I will install electric oil filled radiators which I understand are the safest to use. They demand 500 watts to 1500 watts supply each. The run of cable to a central point of supply is 50 metres. Would it be safe to take the supply from one 13 amp socket on a 2.5mm cable run and then split it to the five cabins. We are a charity and our funds are very limited. Please advise me


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moderators note

appears to be in France
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[mattylad]

Can you be a bit more specific on exactly how much they use?
I.e. Have you 5 heaters that can take 1500w?
That's 7500w in total, way more than 13amp (13a=3000w).

An electrician will be along shortly to advise, and I hope that he notices that your not in the UK?

 

[FrodoOne]

If it is in France, the socket outlet connection used is probably a CEE 7/5 or a (Schuko) CEE 7/3, both of which are rated at 16 A.

At 230 V, a 16 A socket outlet could supply up to 3680 W.

However, what are the 5 separate cabins. Presumably these are 5 separate feline "living spaces" within a building.
Hopefully, the 50 metre, 2.5 mm cable will be within a building and not run outside any structure.

Such a cable will have a resistance of about 0.4 Ohms and, at 16 A, the voltage drop will be 6.4 Volts.

 

[EFLImpudence]

Shouldn't the resistance be double that (0.732Ω)?

Actually 0.9Ω (0.878) for VD calculation.

 

[FrodoOne]

Shouldn't the resistance be double that (0.732Ω)?

Actually 0.9Ω (0.878) for VD calculation.

Yes. I was wrong in my calculation.

I made a mistake in deriving the resistance per metre of 2.5 mm copper.
My source was the table in https://en.wikipedia.org/wiki/American_wire_gauge where I interpolated the 2.5 mm CSA between the AWG sizes (#14 and #13) - but I got it wrong the first time.
Recalculating, I believe that a 2.5 mm CSA copper conductor has a resistance of (approximately) 0.0069 ohms/metre
(Since
#13 is 2.62 mm, with a resistance of 0.006571 ohms/metre and
#14 is 2.08 mm, with a resistance of 0.008286 ohms/metre)

Hence two 50 metre conductors would have a resistance of 2 x 50 x 0.0069 ohms = 0.69 ohms, giving a voltage drop of 11.04 Volts.

 

[EFLImpudence]

Recalculating, I believe that a 2.5 mm CSA copper conductor has a resistance of (approximately) 0.0069 ohms/metre

It is 0.00732Ω/m at the usual 30°C given in the regulations.

 

[satprof]

Do you know what the power of the circuit-breaker (mcb) supplying that socket allows, and are there other devices plugged into that circuit? That may be important as the total load on the circuit may come to more than is currently provided for. (If the existing mcb is less than 16 amps, it can readily be upgraded, but not to more than 16 A without changing the wiring.) If there's nothing that produces much heat already using that circuit, you should be OK to put in a combination of heaters that doesn't exceed 3500 watts, which would be within the allowance for a 16 amp socket & associated circuit. (I know that French electricity can be quite cheap, especially off-peak, but that's going to cost quite a lot to run.)

As for effectiveness, you'll need to consider the size of the cabins, what are they made of & if they're insulated at all? Investing in a lot of insulation might well be a good idea, as 500 watts of heat doesn't go far on a cold night.