Electric rodi solenoid

It does happen and can be deadly. Why do you think Vortechs place the motor outside and others are going to DC controllable powerheads? Float switches in an ATO arc every time the switch on and off so it is especially important in that case.

Having worked in the water/wastewater industry for over 37 years now i can tell you, we use low voltage DC whenever possible for control and places where power is switched on and off often. It is so much safer and makes contacts last many many times longer. If you have ever seen a contact weld together and melt down you would understand completely. We also use relays and fused or circuit breaker protected circuits for the same reason.