Switching 120v between power sources.

[markland556]

Well basically I have a vent fan that I would like to turn on when either a light or an A/C unit comes on. All running on 120v.

I have a controller that powers the A/C and light seperatly.
What I am thinking is have the A/C and light plug in through a box and just have a relay powering the fan if eigther the A/C gets power or if the light gets power.

It seems pretty simple, but I am just a bit stuck. I would really appreciate some help.

 

[crutschow]

If you can detect the power for the A/C and light as simply on or off, then you just need to add two 120VAC relays, one powered from each source. The relay contacts from both relays are wired in parallel to 120VAC and the fan so that when either (or both) relay(s) are on, the fan is on.

If you are trying to respond to the current to the A/C or lamp than that's a little more complicated since you need a current operated relay (which are not common) or a current shunt with detection circuitry.