Electronic – Generic 3 phase relay switch

You should be able to test this yourself at home using household AC mains live as one of the phases L1, and something like a lamp as the load on T1. Keep the lamp neutral going to the wall. Leave L2, L3, T2 and T3 disconnected. This should be easier to troubleshoot.

Crucially check the Arduino control output is holding a voltage over 4V when you are sinking the 50mA 'holding current' in the contractor. You can measure this by turning on the output and checking the voltage at +terminal of the contractor control pins. The device has the 'indicator LED', zero-crossing logic and three opto-isolators sat on your supply. You may find a small logic level MOSFET is needed to drive it, rather than an Arduino pin.

If your drive is inadequate you may be in the position where some, but not all phases fire, (given the zero crossing detect will stagger the start-up) which is not great for the pump as it will stall but still be dissipating power. So until you fix this, don't leave it running for long periods.

I think you are pushing the 4066 far beyond its limits by powering a relay coil from it. The chip heats up to a point that the other switches fail too ("current apparently bleeds over to SW2"). If the chip still functions after you manually 'reset' it by removing power to it, I think you are just plain lucky.

The solution will be that you power your relay with a separate transistor (and flyback diode). A bit like this answer