Size of cable for 12KW electric boiler

[Ant1]

In a few years' time I am thinking about upgrading an old back boiler to an electric boiler (due to flue restriction as this is the listed building, therefore I won't be able to use gas anymore).

I would like to know the size of the cable I require for a 12KW boiler (Gold Potterton - https://www.mrcentralheating.co.uk/...uct/Potterton-Gold-Electric-Install-Guide.pdf).

Is 6mm2 or 10mm2 suitable? I used some calculators that advised more than 10mm2, but I never came across such big cables (at Screwfix / Toolstation), they do not seem that common in domestic dwellings.

Since the floorboards are remove due to a refurbishment, I wanted to take the opportunity to install a spare cable before installing the laminate.

PS: the length of the cable will be less than 10 metres, around 9 metres.

Thanks!

 

[flameport]

Very likely 16mm².
There is also the very important question of whether the electrical supply is adequate for such a ridiculously large load. Plenty will not be.

Electric boilers are the worst possible choice for heating anything, and also the most expensive to run by far.
Pretty much any other type of heating would be preferable.

 

[Ant1]

Electric boilers are the worst possible choice for heating anything, and also the most expensive to run by far.
Pretty much any other type of heating would be preferable.

I agree John, this is something I have trying to avoid for a long time. One day my back boiler will break down, and since they do not make them anymore I am stuck; I cannot install a conventional combi boiler as I am not allowed to drill through external walls (the flat is in a listed building)

 

[EFLImpudence]

Very likely 16mm².

May we ask why?

 

[JohnW2]

May we ask why?

I suspect it's probably because he doesn't seem to think that Method C is often used.

Kind Regards, John

 

[flameport]

Method C is all you have got for 10mm². Possibly B but that involves running the cable pretty much at it's maximum permitted operating temperature.

16mm² reduces cable heating losses by 31 watts compared to 10mm², which is not trivial for an item which will be on for hours everyday.
It also reduces the cable operating temperature significantly.

I cannot install a conventional combi boiler

Hot water cylinder with electric immersion heater and individual electric panel heaters in each room would be far better.

 

[Notch7]

I would just use 2.5mm as you are never going to be able to afford to switch it on.

 

[JohnW2]

Regarding my original question, would 10mm² be safe?

As has been said, the current-carrying-capacity of 10mm² cable would be adequate if it were installed (for its entire length) by 'Method c' (clipped on surface of walls, buried directly in plaster etc.

However, as flameport has said, that would mean running the cable at close to its maximum operating temperature, and would result in more 'energy loss' in the wiring (than with 16 mm² cable). That may well not be an issue in Winter, since the heat generated in the cable would heat the house, rather than being 'wasted', but would constitute 'wasted energy' at times when heating was not required. Beyond that, no matter what the cost of electricity, the cost of that 'wasted energy' would fade into total insignificance in comparison with the cost of running the boiler. I've not checked flameport's figures, but if he's right that the difference between 10 mm² and 16 mm² would amount to about 31W, at a price of 30p per kWh that would cost just under 1p per hour, as compared with about £3.60 per hour for the boiler itself.

Is 6mm2 or 10mm2 suitable? I used some calculators that advised more than 10mm2, but I never came across such big cables (at Screwfix / Toolstation), they do not seem that common in domestic dwellings.

The largest size of T+E cable available is 16mm, but that is readily available from any electrical wholesaler. It's more difficult to work with than 10 mm², but, again, the price difference between 10 metres of 10mm² and 16mm² cable is really totally irrelevant in the context of what you will be paying to run the boiler!

Kind Regards, John

 

[Ant1]

Thanks John.