Relay to monitor when 120v fan is switched on

[JJ1234]

I want a PLC to know when a 120v switch is turned on that powers an exhaust fan.
I need to know what kind of relay would work and how i can tie it in to the 120v power line of the fan.
I was planning to put the relay in the 120v line in an electrical box and run 24v from the plc to that box.

 

[parky]

Any kind providing the coil voltage is 120v, is there not a contactor that switches the fan on with a spare contact or could you add an auxilliary contact

 

[JJ1234]

Any kind providing the coil voltage is 120v, is there not a contactor that switches the fan on with a spare contact or could you add an auxilliary contact

Its switched on with a basic light switch.

 

[parky]

Ok then just a small relay with 120v coil, the contacts need not be high current as a digital input on a PLC is only about 10ma