Current operated switch

Here is one we prepared earlier for you:

Thanks for the suggestion - seen that - was really looking for an off-the-shelf-solution Surely I'm not the first person on the planet to have this problem?

No status light on the EV charge point you can tap into?

There is, but it gives 'plugged in' status rather than whether its charging or not. The car has a timer which I set to start charge at the start of the economy 7 period.

Modify one of the "slave power" controls used for PCs

A relay/contactor. Rewind the 240v etc coil to give the right number of amp-turns with wire as thick as possible. 5A seems an odd threshold though.

NT

You can get shower priority units eg

EV as 'no 2' and boiler as 'no 1' so the EV gets continuous charging except when the boiler control is calling for heat.

Owain

Thanks for that, almost exactly what I need - with a bit of bodgery I think it will do the job.

Andy

Digging around further, I think I only need one of the componets of this unit, the priority relay. A quick google finds several DIN mounting types - a lot cheaper than buying the whole shower controller. Just put the EV load through the relay, and the clean contacts tell you if it pulling over 13A or not - absolutly ideal. Didn't know these things existed!

Most of the off the shelf solutions will assume the load you want to monitor can be fed from a 13A plug. Less useful for high load fixed radial circuits.

True, but I believe they use the voltage drop across a pair of back-to-back diodes as the sensing circuit, so these could easily be beefed-up. The output would drive a contactor. But it seems that a "priority relay" is the thing - I hadn't heard of them until this thread.

Yup, not looked at them before either...