Shunting a single 20a ckt.

[hillbilly1]

If you need to do like what @LarryFine has posted, this contactor is the most economical way to do it. The contacts can be changed easily from N/O to N/C by which position you install the contact block in. Use the N/C position to turn on the fan, while using the N/O to turn the make up air off. (Series the make up air fan controls) Square D also makes a contactor that the contacts can be changed, but it’s more involved.

 

[Jha]

Cutler hammer CHF120ST

 

[Jha]

Just out of curiosity, if theoretically you had to use a GFCI breaker, would take the 2 control wires and take one of them to the neutral pigtail of the GFCI breaker and the other control wire to the ground?

 

[Jha]

It works, but probably not a great idea, the higher the available fault current the worse of an idea it may be. At very least how do you know you didn't destroy the light duty contact when you test it or it actually functions? May not work next time it is called on. You want low current to assure this doesn't happen.

An idea I never have done but have given some thought to is to use a GFCI breaker and create a neutral to ground fault with the control circuit.

Would you be using the control wires the same common and NC to the neutral screw on breaker and other control wire to the ground? I’m confused how that would possibly work?

 

[hillbilly1]

Would you be using the control wires the same common and NC to the neutral screw on breaker and other control wire to the ground? I’m confused how that would possibly work?

Creates an alternate path for the neutral current, so the breaker thinks there is a ground fault (actually, it is)

 

[Jha]

Creates an alternate path for the neutral current, so the breaker thinks there is a ground fault (actually, it is)

So the control wires same ? NO to neutral screw on breaker and common to ground?

 

[hillbilly1]

So the control wires same ? NO to neutral screw on breaker and common to ground?

Yes, in theory it works, but not designed for that type of application. Load neutral and N/O tie together on the load neutral screw.

 

[Jha]

Yes, in theory it works, but not designed for that type of application. Load neutral and N/O tie together on the load neutral screw.

And then common to ground? Seems odd cause when you put a meter between the two you get nothing

 

[hillbilly1]

And then common to ground? Seems odd cause when you put a meter between the two you get nothing

When the contact closes, it parallels the load neutral, shunting some of the current, which in milliamp’s doesn’t take much. You can test the theory with a gfi receptacle, take the load neutral to ground, and it will trip.

 

[Jha]

10-4 thanks for clarifying

 

[kwired]

Class A GFCI's have a neutral to ground detection component. What it does is inject a signal that will travel through the output neutral through when faulted through the ground and back to the source then back to the GFCI via the ungrounded conductor. It will draw enough mA to trip the breaker on it's usual trip function.

Without that feature there needs to be enough load current so that the alternate path causes enough imbalance to cause the trip, so it won't work during a neutral to ground fault if there is no connected load at the time.