Connecting an immersion heater

While normally placed on their own circuit, sharing with the heating controls sounds fine as well since they are unlikely to be more than a couple of amp at most.

At about 4amps/Kw that's 12 amps for the immersion heater plus ? for the shower could be getting on for 18-20 amps. It depends how the shower is wired, might just be on it's own 15 amp supply, which wouldn't take the extra load.

Shower is upstairs and not on the circuit under stairs.

Boilers are (typically) powered by a five amp fused spur off an existing ring main. So that wiring is unlikely to be man enough for the job.

As a *really* temporary fix I suppose you could run it off a 13 amp plug and socket. You must use adequate cable, it *should* be heat resistant cable close to the heater but you might get away with it for a month or two, especially if it is in free air (and not, for example, covered with extra thermal insulation).

Even high quality plugs and sockets such as MK don't like being wired up to immersion heaters for too long. I know because a mate of mine had this arrangement in his brewery, at one time.

I think that running it off a proper 13A switched and fused spur is within the regs (but John or Adam will be along in a minute to correct me).

Thanks. I guess the key is whether there are other things on the heating controls circuit. Controls are off anyway. I'm trying to read the scawled legends on the CU - think I'll have to find a magnifying glass....

Agreed but 3 KW is 13 A. The heating circuit *may* have a 6 A MCB, worth a check.

I'd try and avoid the 13 A fuse, passing 13 A for a reasonable amount of time it's going to get warm if not hot... A 20 A DP switched connection unit and 2.5 mm fixed and flexiable wiring through out with a 16 A MCB would be fine and if a radial from the CU how it ought to be installed anyway.

John Rumm explained :

As a very temporary solution, it will be just acceptable to connect it via a 13amp plug, into a socket. Your heating control circuit will likely be only 3 or 5amp amp fused.

As a temp supply I would use your suggestion and just plug it into the nearest socket.

Although the OP might find that the immersion does not work. So he would certainly be better off trying your suggestion to find out if it works before buggering about with 20A DP switches etc..

I did this last year in a hard water area. There was a massive bang and then the sound of lumps of limescale dropping down the inside of the cylinder. Probably a 30 year old element that had never had a volt across it.

Cheers

Good point. I usually fish out the megger before connecting something new......but not always :-)

And I suppose I should also have said make sure the heater has a thermostat in series! With a "not installed" system it is not beyond the bounds of possibility that the thermostat is missing, and that an inexperienced person might just try connecting mains to the heater element.

Good point.

It's now supposed to be two thermostats in series.

But the OP should INHO test the element before buggering about with the stat(s). 230V should do the test:-)

Glad to see you back. How's the er....

shuffles feet....

michael adams

...

you are using 240 V in your I = P/V calculation.

Due to EU hamronisation, system voltage is now closer to 220 V so that makes I = 13.63A......

Had the dry cough and aches, took the day off work.

The aches were probably because I am getting too old to build and climb a tower scaffold and lump up light fittings and then the cough turned into a cold.

So I am not bothering with a test.

It's 230V (give or take +10/-6%) in the UK.

A 13A BS1362 (plug fuse) will not trip at 20A for a long time.

...and supposing it is a 240v element running on a 240v supply?

Good to hear it. Its probably only when you get a high temperature and lose the sense of smell or taste* that it's time to take a test. Unless you're feeling really rough. In which case you probably wouldn't want to get out of bed in the first place.

I take every precaution but I've had a mild cold for weeks, which I'm keeping to myself.

michael adams

Except that it wouldn't as the resistance of the element doesn't change.

220 V and 19.2 ohms I = V/R = 11.45 A and P has also dropped to