Electronic – arduino – Connecting DIODE in relay circuit

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.

This sounds like a good application for regular old mechanical relays. They won't care about the direction of current, won't have a offset voltage, and their off leakage is zero in a practical sense.

Relays that can switch house power are common and available in a variety of coil voltages. Since you say you want to switch "lights", it seems like the current will be low. Relays that can do this will be small and available in coils meant to be driven from 5 V. This means you can run them from the same power supply as the processor doing the controlling, but not that the relays can be run directly from a digital output. You will need a transistor controlled by the digital output that in turn controls the larger relay coil current. Don't forget the reverse diode accross the relay coil, else you'll end up with fried transistors.