3-phase electric heater control by SSR insted of contactor.

Hello Everyone,

Does anybody tried to connect heater pipe(400VAC, 3 phases) to the SSR instead of contactor? I know that this kind of solution is now more and more popular, But i dont have any idea how to do it?
As far i know usually it is realize by using combination of two SSR and one contactor... Maybe some one have more knowledge and know more details..

I've never seen it done with a contactor and SSRs, but I imagine you would switch all 3 phases with the contactor and two phases with one single-pole SSR each. When it's time to turn it on, you would pull in the contactor first and then turn on the SSRs. To de-energize the load, you would turn off the SSRs first and then drop out the contactor. This way, the SSRs handle the inrush and back emf to prevent arcing at the contacts. This is just me thinking about it, though; I've never done it. I would still push for a proper 3-phase SSR unless there are serious price/lead time advantages to the other way. And even then I would probably consider the contactor route temporary until the right SSR can be installed.
Be aware that the failure mode of an SSR is un-safe, an SSR can fail in ON state, continuing to conduct electrical power and the control signal cannot turn the SSR off.

In the US, ovens, kilns, and furnaces are required by code to have a 'safety shutdown' contactor in series with an SSR controller. The contactor is typically controlled by a temperature 'limit' controller, which trips when the temperature is too high, an indication of possible SSR failure. The temperature sensor, limit controller and contactor constitute an independent, safety circuit.
joseph_e2 and David_2 are correct in their circuit descriptions - such principles of safety operation are used worldwide

The same principle also applies to single phase contactors and SSR's.