I am a physicist by training but have been tasked with designing a heating controller box for a custom application that will be used in an industrial setting. I would like to make sure that I am following best practices before I follow through on assembling the control panel.
I want to simultaneously drive up to 4x 3 phase - 480v - 3kW heaters (configured as a 3-Wire delta) using an on-off cycle rather than actual PID to save switching lifetime and complexity. Based on my calculations the per phase load of each heater should be about 3.7A. I was planning to use contactors to switch each phase and I wanted to make sure that it would be kosher to drive all 4 contactor relays in parallel from the AC Relay output of my selected temperature controller.
The controller SL4848-RR is rated for 5A AC (240v) output and the contactors WDP25-3L-230 have a typical input power of 10VA@230V and inrush of ~50VA. This would put the peak power draw at <250 VA Peak to run the controller and and contactors off of my control transformer PH350MQMJ which is rated for 350VA at 240V. If I place the coils of the contactors in parallel I expect the total resistance to drop by a factor of 4 and the current to be shared equally across the coils of each contactor at the peak current of 200VA and running current of 40VA. Is this naive to assume? Should I explore a different configuration? I also assumed I don't need a flyback diode because the coils are AC driven, but this may also need to be revised.
For extra context:
I have selected 20A FAZ-B20-3 input breakers for each phase input and I will be placing supplementary breakers FAZ-B6-3 on the high side of each contactor with a per phase rating of 6A (3.7A/80% for thermal overhead and derating for worst case T of 50C). All breakers were selected with B type curves as these loads are 100% resistive. The control transformer will be powered on two of the input lines.
TIA and don't hesitate to ask for more information.