Relay with momentary switch

Thread Starter


Joined Feb 5, 2010

I can no longer locate the thread where a poster was asking how a two way momentary switch could be used to power a heater(I think it was automotive related and closed). He wanted to be sure that both outputs could not be on at the same time. Here is the relay logic circuit for doing this. activating one relay will de-activate the other.

There is no way I can see of turning off both once one is activated using only the two way momentary switch. I had to add another switch to perform the off function. A switched 12 volt source would not need the off switch.


Joined Sep 3, 2009
The relay logic diagram that Kermit posted is basically an Electrical Interlock used extensively in industrial motor controls.

The interlock keeps power from being applied to the motor to make it go in both directions at the same time (along with a mechanical interlock located in the relay itself).

Just thought I'd add my two cents