thanks that's a good explanation, I had a vague idea of relays but forgot since its been a long time I read about them.

still I'm not 100% clear on it. the relay will be my switch to turn on/off connection between VFD ports. relay has 3 pins : NC/NO/VLIN
-connect 24v to VLIN ?
-connect X1 to NC ?

or

-connect COMM to VLIN
-connect X1 TO NO

or

-connect 24v,comm,X1 to NC,NO,VLIN

sorry for sounding stupid but I need to be sure and understand correctly.