Relay spst vs spdt

Thread Starter


Joined May 15, 2015
So I have an AC circuit interrupted by this old relay board. It has 2 connections on its channel, which is basically where i run the circuit wire thru. Its an SPST-NO relay.

I have to switch over to this spdt switch and I need to wire it up. How would I wire it up in that case based on my 2 wires from the spst relay?

Im thinking i would need to connect one of the wires to the Common and the other wire to any of the 2 terminals (NC/NO)? Probably NO.


Joined Feb 20, 2016
If you want the power to be on as the relay is operated, use Com and NO.
To have the power off with the relay operated, use Com and NC.
NO = Normally Open and NC = Normally Closed. These are the state of the contacts with the relay not energized.