On Wednesday, 30 September 2020 00:29:15 UTC+1, Roger Hayter wrote:
On 29 Sep 2020 at 20:58:34 BST, "No Name" wrote:

On 29/09/2020 19:14, Harry Bloomfield wrote:
John Rumm explained :
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.

3kw immersion heater = 12.5amps !

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.


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......

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.

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