Connecting an immersion heater

[John Smith]

Arrgh - the cylinder was installed about 17 years ago and in London it's hard water. Maybe this is not such a good idea...

[Roger Hayter]

You might think that, but usually UK sold immersion heaters are 3kW at 240V. This is a few pence cheaper for the maker, and in practice we stiil have 240V. Although it is harmonised to be a nominal 230 plus or minus a tolerance this is actually so far a paper exercise only.

[tabbypurr]

A lot of people don't seem to realise that while the harmonised spec is nominally 230v, part of the plan was, and still is, to keep France 220v and UK 240v for the benefit of old appliances. 220 & 240 are within the new 230v spec. If you're in the habit of measuring mains voltages it won't take long to realise the current UK target voltage is 240 not 230.

And fwiw there is no such thing as 230v versus 240v immersion heaters. All marked either voltage can run on the other. Some old ones have a list of voltage versus power on them, sometimes covering everything from 200v to 250v.

NT

[tabbypurr]

The circuit might be on a 5A or 6A fuse/mcb, but it's the cable rating that matters, fuses & MCBs can be changed. The wiki gives the ampacity of the usual cables.

If you use a mains plug, beware that some really can not handle 13A continuous for a long time.

NT

[David Wade]

Generally they are rated 3kw @ 240v. Lower voltage and you get less out and they stay under 13amps

Dave

[David Wade]

You could install a new one, but getting the old one out without distorting the tank might be fun. My tank had a blanking plate and I installed a heater.

Dave

[Dave Plowman (News]

Boiler etc controls don't take much current. If they are fed off a ring via an FCU, check the size of the cable used. Most would use lighting cable.

[Vir Campestris]

I caught a mild cough on a 'plane on the way back from California in February. I still have it.

Andy

[John Rumm]

A couple of points to keep in mind. The EU wide voltage spec is 230V

+10%/-6% a loose spec that includes all the common generation voltages used in the EU states.

However our generation voltage has *not actually changed*, and is still

240V. But 240V is within the allowable spec of 216V - 253V

For design purposes however we use 230V

Lastly for a resistive load, lowering the voltage does not result in it drawing more current to compensate for the lower voltage to maintain a given power output. If its actual power output at 240V is 3kW, reducing the voltage to 216V will drop the power output to ~2.4kW, at 253V it would rise to ~3.3kW.

(the heaters documentation will normally specify at what voltage the output was calculated)

[Dave W]

My immersion heater is 3kW and plugged into a 13A socket via a clockwork timer.