Re: 240v Temp controller & 120v contactor?
Contactors can have different voltages for the load and for the coil (solenoid). If you going to use 240v heaters, you want a 240v load contactor. You will also want the contactor to safely handle the amperage created by the heaters. The contacts are rated in amps. If you have two 3kw heaters on 240v, that's about 12.5A per coil individually but run in parallel, it's about 26A. (slightly more than double) Your contactor should be rated about 30A or more.
The solenoid coil on the contactor can be anything from 6vac to 440vac. If you want to run the contactor on 120v, get one that has 120v coils but make sure the contacts are 240v/30A+.
As a side note. I strongly suggest you use Solid State Relays (SSR) instead of contactors. Depending on the controller you use, the contactors will wear out in a hurry. SSRs will switch on 3-32vdc and will handle 240vac/30A+. SSRs can be switched directly from the SSR output on a controller. SSRs can also reduce light flicker in the shop since they switch on the zero boundary of an AC cycle. They don't shock the circuit like a contactor.
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