water heater circuit

[stet19]

Hi

I'm installing a new radiator in the bathroom connected to the central heating system. I intend to have an electric element for occasional use in summer.

I want to use the separate supply to the immersion heater in the hot water tank to supply the element. I have never used the immersion heater - the water is normally heated from a gas-fired boiler - but I want to keep the capability.

I know it would be wrong to extend the heater circuit. My question is: is there a household changeover switch so that they can't both be on at the same time and is that legitimate

 

[Diyisfun]

Its usual to have the immersion on a manual switch, to do what you want I don't think would be simple.
But why would you want it?, you will use the gas always unless you have a failure, then you would manually change to electric.
Thats how I and I am certain most people would use & do use it.

 

[Scoby_Beasley]

I've said this before, but if you live in a hard water area your immersion can fail due to lack of use/coating up. use it occasionally (monthly ???) to keep it "clean".

 

[mapj1]

It is OK, but non-standard, to use a suitable double pole double throw switch as a change-over so both cannot be on at once.
Similar things can be done with houses with 2 showers or 2 cookers.

However, like new exam questions confuse both students and examiners, and are not popular with either, so do departures from standard circuits, so these need to be clearly labelled and there needs to be a better reason than ' it was easier than running a new wire to the board' before you do it.

Note whne considering loading that a 16A MCB will blow before a 13A fuse, at all currents.

 

[kevplumb]

think he means an electric element in the rad/towel rail guys

 

[mapj1]

yes, thats how I read it too - but to heat his towel rail from the feed that would have done the immersion, but to wire it as either/or
and I stand by 'its non-standard and I dont recommend it' !

 

[plugwash]

Hi

I'm installing a new radiator in the bathroom connected to the central heating system. I intend to have an electric element for occasional use in summer.

I want to use the separate supply to the immersion heater in the hot water tank to supply the element. I have never used the immersion heater - the water is normally heated from a gas-fired boiler - but I want to keep the capability.

I know it would be wrong to extend the heater circuit. My question is: is there a household changeover switch so that they can't both be on at the same time and is that legitimate

you could use a switch like http://www.tlc-direct.co.uk/Products/KMT338212I.html

then you have one position for the immersion heater one for the heated towel rail and one for off

its unusual but i can't see anything wrong with doing it especially if the immersion is very rarely used.

 

[stet19]

Thanks guys. Sorry I wasn't here to clarify but yes it is a heating element for a towel rail that I'm installing.

Scoby thanks for the advice on preserving the immersion heater. I'd never thought about it before.

I'm surprised that my proposal is so unusual, it seemed the most convenient solution. However, and much as I like the idea of fitting that impressive changeover switch (thanks Plugwash), it may be better to take a spur off the ring main as its only a 200W element I'm fitting (assuming that's ok ).

 

[ban-all-sheds]

I can't see anything wrong with using the immersion circuit. Without a changeover switch. An extra 200W won't overload it, so provided you use an FCU with a 3A fuse and document what the circuit is for you won't be doing anything dangerous.

 

[stet19]

Thanks sheds. That'll do for for me. I just assumed that such a spur (although not necessarily dangerous) would be illegal.

 

[ban-all-sheds]

It's not illegal, and it is not dangerous.

The worst it could be is contrary to the IEE Wiring Regulations, which does not make it illegal, but should give you pause to check that you have covered all the bases:

What's the capacity of the cable given how it's installed.
Is the maximum load less than the rating of the MCB which in turn is less than the capacity of the cable.
Is the circuit appropriately labelled at the CU so that it is obvious how to isolate the towel rail.

 

[stet19]

Thanks again. The 3kw immersion has its own labelled 16A MCB in the CU, so there is no problem with the additional 200w towel rail heater - 3A fused switch appropriately labelled of course

Just a thought - 1mm cable is more than adequate for the load, but would this be unacceptable for other reasons.

 

[Adam_151]

You should connect the supply side of the fcu to your existing 16A radial circuit using 2.5mm cable, but if fuseing at 3A, you can connect the 200w load to the load side of the fcu with 1mm if you wish (though you might want to use 2.5mm cable to avoid purchasing a different size of cable, nothing wrong with using thicker cable than necessary, as long as you can connect the ends ok), also don't connect the twin+e direct to the heater, use a flex outlet plate, but make sure this goes in the appropiate part of the bathroom though (zone 3, or out of zones, IIRC)

EDIT:

or if you are putting the fcu near the load, (remember the zoneing) , get one with a built in flex outlet, 2.5mm twin+e earth from the 16A radial circuit to the supply terminals, flex from the load terminals, out through the flex outlet hole, and to the heater and stick a 3A fuse in it.

 

[stet19]

Understood. Thanks for all the advice guys.

 

[ban-all-sheds]

And if it's going on a tiled wall, a bead of silicone sealant run around the edge of the faceplate just before you fully tighten the screws is a good idea.