I recall reading here @ RV.net (could be another place memory is not all that good anymore aka CRS) that a relay used in a transfer switch application should have a 12Vdc coil as compared to a 120Vac coil. As I recall it had something to do with chattering of the contacts and the associated electrical noise created.
Might be your issue??
The relays I have been using are
Potter & Drumfield
DPDT 30amp contacts @240Vac
with a 12Vdc powered continuous duty coil drawing about 400ma
Managed to salvage 12 of them from an old Heart Interface Inverter/charger with integrated 50amp transfer switch
Did you "bond" your inverter?
Morningstar Puresine instructions say to take the 12Vdc input "-" connection to one of the AC output terminals thus bonding the inverter output. Otherwise both float at about 60Vac above "-" which is my chassis common.
I connected one branch of my AC distribution panel's output through the NC connections of the relay, The inverter connected to the NO connections activates a small 12Vdc wall wart providing 12Vdc to close the relay.
This way no worries about switching off the Converter, Frig, Water heater or Microwave. They are never in the inverter circuit.
