I am having a problem with a 36kw Industrial Hot water tank. It is a 3 phase supply with neutral and earth. A thermostat controls a contactor which brings in the element. The contactor has a 220V coil so the circuit is separated into control and main circuits. The main circuit just has 3 circuit breakers which connects to the top of the contactor. The element is connected to the bottom of the contactor with the neutral connected to a neutral bar.The control circuit is just a single pole circuit breaker connected (at L1) to a thermostat and then connected to A1 of the contactor coil. The A2 is then connected to the neutral bar.
Heres my problem:
As soon as the thermostat is switched on the contactor should pull in and start the element. Problem is it DOESN'T! When I check the voltage on the coil I get 0V but check between L1 and N I get 0V and L2 and N I get 400V and L3 and N I get 400V? Even if I bypass the thermostat and connect L1 directly to the A1 and neutral to A2 it still doesn't bring in the contactor. The are no phases missing and the neutral is definitely there. I have proved this by switching off the control circuit and then testing between the phases and then line to neutral and everything is correct. It just when I turn on the voltage goes bye bye on L1
Funny thing is that when I manually push in the contactor is stays in and then when the tank reaches temperature the thermostat kicks out the contactor as it should. Very weird for me as this has never happened to me before.