Hooking up portable generator to automatic transfer switch?

Wouldn’t an ATS require the generator to automatically start? Or are you just talking about tapping into the system through the ATS?

Is it a generic Generac TS or one of the ones you buy w/ their generators? If it is the generic one It may work and if it is a service entrance one you will need to turn off any breakers you do not want to power in your panel bc it will transfer the entire load to the generator. You may also be able to manually transfer it too.

If it is one of the others, it is pretty much useless w/o the generac unit. All the “smarts” for those are located in the generator. You could probably rig something up to get it to transfer.

What model is the transfer switch? That would help get you a better answer.

You should be able to do it with that one, but unless you get creative with a way to control the transfer switch here is what you will need to do.

Shut off the main breaker in your inside panel and all the other breakers.

Shut off the breaker in the Transfer Switch.

Use the manual transfer bar / tool thing, to manually transfer the switch to gen power.

Start your gen and plug it in.

Turn on the main breaker on the inside panel

Turn on the circuits you want active.

To transfer back to utility, reverse the procedure.


Try as best you can to balance the load on each leg of the generator and keep in mind each leg will be able to put out about 1/2 the gens rated wattage.

You have full wattage at 240, but only half per leg at 120v. One side of your panel will be on one leg and the other side will be on the other.

Be careful hooking up the gen wires. You have live utility voltage in the transfer switch even with the breaker turned off. Make 100% sure you wire the plug correctly too.
On the plug
X & Y. Will be the two hot legs.
W will be neutral
G will be ground

Size your wire based on the breaker on the gen. 12/3 for 20 amp and 10/3 for 30 amp.

For auto transfer that switch uses 240v to power the transfer coils and It looks like a 12v relay to control the coils. Just FYI.

How big is your generator?

I would be a little leery of having it instantly switch back to utility. You really need a little delay to make sure the power is stable. With his setup, every time the utility energizes it transfers back.

If you don’t have a generator with at least 15kw there is a good chance you smoke it and some of your electronics if you don’t shut off the inside breakers before transferring. You are going to have to manually manage the load.