I have electric baseboards from the mid-80s. I am looking to buy the MYSA thermostat, and I am checking compatibility. I am pretty sure my current unit is a single pole thermostat, but I am a bit confused by this third wire listed as "common" on the thermostat. Just quick read online its use for smart thermostats to provide constant power, but this by no means is a programmable or smart thermostat...I have attached my system as well as MYSAs install diagram. Its on a double pole 20 amp breaker so I am on the assumption it is 240 V even though I don't see a red wire.... Any guidance will be helpful...

 

Hi, that should work fine, their website has a compatibility chart that is quite good.
Geo

 

I labeled your picture for the connections. It appears that thermostat controls two baseboard heaters.

 

Thank you! The lady kept saying it was not compatible because it was 4 and not 5 wires but I think she is just reading off a script. You are correct there are two baseboards in the room

 

The wire count is different since you have both heaters arriving there. Connect the wires as I've shown and you will be set. Be sure to mark the L1 black wire so as not to get it confused with the two load black wires.

In your plastic box.... the cable in the upper left corner is the incoming hot line.