Designing a Transfer Switch: Difference between Contactor and Relay?

[再生可能 エネルギー]

I am designing a transfer switch to power a Heat Pump so I could select between using the Grid or Solar Energy,
or even turning off completely the Heat Pump for service, or running only on Solar Energy if available and be off otherwise.

I try to understand the difference between a Relay and a Contactor, and what would be the advantage of one over the other?

- I have been using previously, for another project, an 80A Relay JQX-62F-2Z but I would like to turn off the load, so I would need to have two separate relays.

- Also, I would need to add a timer so the Heat Pump motor could be turn off before restarting to avoid the out of phase issue between the Grid and the Inverter.

- If that possible, I would prefer having a latching mechanism, so the coil for the switch would not be always draining current.

- I would need to have some protection, so the Grid and the output of the Inverter could not be activated at the same time.

So what would you your recommendations, such as using Relays, Contactors, or even Solid State Relay, and is there any switch combining timing and latching mechanism?

 

[Mike 134]

In the electrical industry when someone says they are using relays it's typically used with control circuits 10 amps or less, contactors are made for switching heavier loads on and off.
Old Ideal Chiller starters had contactors rated for 1600amps

 

[Supervstech]

Agreed.
A contactor is a relay designed to handle motor starting loads.

 

[SparkyJJO]

A contactor is a relay's (much) bigger brother.