Changeover switch

[ALAN/ALAN D]

Hello Paul

A normally closed / open contactor will have a much faster transition than the thermostat and excess thermal cut off device in the immersion heater.
They would fail well before the contactor if D.C. voltages were being switched. The Iboost controller should be designed knowing that the immersion heater temperature devices down stream of the Iboost must operate safely. I Do use solid state relays in my projects because they can control pulse width modulation better and they require far less power to operate saving power loss.

[Tinbum]

If you wanted to be extra safe with the contactor because of the dc you could use a 3 phase contactor 4 pole and put it through a couple/ three times.

[Tinbum]

Note you don't have to change the immersion thermosat and that is just an ac switch for the iboost.

Edit, sorry hadnt seen your post Alan.

[Gareth J]

No need to switch Neutral.

Lovely diagram!