Automatic Transfer Switch for portable Generator

ubbrez

New member
Location
Levittown, Pa
I have been asked to provide an automatic transfer switch for a portable generator. Specifically a 8 circuit, 100A (rated) Generac ATS. The purpose being , that during a power outage the customer could plug their portable generator into a 30A inlet which is wired to this ATS, they would manually start their generator (located outside)and the transfer switch (located in basement next to panel) would automatically sense emergency power and transfer his 6 EM circuits on. This eliminates the customer from having to start his generator then walk thru his dark home down to the basement and manually switch his emergency breakers on. SO here lies my problem/ question. The ATS requires a 24 volt relay to fire/ energize in order to actuate the transfer switch. The 24 Volts is supposed to be provided by a stand alone generator that the customer does not have. He has this portable gen. So why could he not install a 120 volt primary to 24 volt secondary transformer inside his ATS, use the 120 volt power provided by his portable gen to power this transformer which will then power the 24V transfer relay and switch his emer circuits on. Besides voiding the manufacturers warranty for changing/ altering the product, can anyone think of any other code or safety reason why this can not be done?
 

Smart $

Esteemed Member
Location
Ohio
What is the calculated load on those 6 EM circuits?

To use an ATS, the calculated load (continuous loads, if any, factored @125%) must not exceed the 30A breaker rating on the generator.

As an added note, installing the control transformer, and proper fusing, in an enclosure separate from the ATS, would be less likely to void ATS manufacturer's warranty.
 

kwired

Electron manager
Location
NE Nebraska
Another option - place manual transfer switch in vicinity of the generator - then you don't have go find it in the dark after starting the generator.
 

Smart $

Esteemed Member
Location
Ohio
Another option - place manual transfer switch in vicinity of the generator - then you don't have go find it in the dark after starting the generator.
I agree. An MTS, outside near generator as you suggest, and a 6-circuit subpanel is a better option than what the owner wants. Also permits a calculated load over 30A.
 

ceb58

Senior Member
Location
Raeford, NC
In a normal set up N1 N2 is the utility sensing circuit. When utility is lost gen starts and then sends 24v back to ATS on 194 & 23 to transfer. When utility returns control panel senses power and starts shut down.
Now what you plan would work to supply 24v to 194 & 23 but now you have the problem when utility comes back. The switch will not transfer until you remove power from the transformer. That could be a problem if they don't realize utility is back on.
I agree with every one else. Set a double throw switch with an power inlet feeding a small sub panel near the gen. He's going to have to be out there any way to start the gen. Start gen, walk over to switch, throw switch, go back inside.
You have stated you know that you would void the warranty by doing what you propose but you are creating a code violation by modifying the listing of the switch 110.3(B). And you must calculate the load transferred to insure the generator can handle the load 702.4(B)(2).
 

Barbqranch

Senior Member
Location
Arcata, CA
Occupation
Plant maintenance electrician
Since he is not powering all his loads w/ the transfer switch, all he needs is to turn on some lights that are not on the transfer switch.
 

Smart $

Esteemed Member
Location
Ohio
Since he is not powering all his loads w/ the transfer switch, all he needs is to turn on some lights that are not on the transfer switch.
:ashamed1: Good point. Between posts I forgot it was a part load setup. Mine is full load.
 

kwired

Electron manager
Location
NE Nebraska
In a normal set up N1 N2 is the utility sensing circuit. When utility is lost gen starts and then sends 24v back to ATS on 194 & 23 to transfer. When utility returns control panel senses power and starts shut down.
Now what you plan would work to supply 24v to 194 & 23 but now you have the problem when utility comes back. The switch will not transfer until you remove power from the transformer. That could be a problem if they don't realize utility is back on.
I agree with every one else. Set a double throw switch with an power inlet feeding a small sub panel near the gen. He's going to have to be out there any way to start the gen. Start gen, walk over to switch, throw switch, go back inside.
You have stated you know that you would void the warranty by doing what you propose but you are creating a code violation by modifying the listing of the switch 110.3(B). And you must calculate the load transferred to insure the generator can handle the load 702.4(B)(2).
I haven't been around many ATS systems, but something isn't adding up here - normal ATS setup generator sends 24 V back to ATS on 194 & 23. Modified setup described here - generator is still the source ultimately providing a 24 volt signal back to 194 & 23, what is different as far as ATS is concerned? Or is utility sensing circuit in the generator controls instead of in the ATS controls?

Add: a simple fix if that is true is to place a control relay in the 24 volt signal and interrupt that signal when utility resumes, you can even put a delay on it if you want to ensure stability in utility. You may even want to set up a kill system of some sort to shut down the generator. Don't put too much into this though or you may as well have bought the generator that goes with the ATS in the first place.
 

ceb58

Senior Member
Location
Raeford, NC
I haven't been around many ATS systems, but something isn't adding up here - normal ATS setup generator sends 24 V back to ATS on 194 & 23. Modified setup described here - generator is still the source ultimately providing a 24 volt signal back to 194 & 23, what is different as far as ATS is concerned? Or is utility sensing circuit in the generator controls instead of in the ATS controls?

Add: a simple fix if that is true is to place a control relay in the 24 volt signal and interrupt that signal when utility resumes, you can even put a delay on it if you want to ensure stability in utility. You may even want to set up a kill system of some sort to shut down the generator. Don't put too much into this though or you may as well have bought the generator that goes with the ATS in the first place.
On a normal set up the "brains" of the operation is in the generator ether with the nexus controller or the evolution controller the ATS is a "dumb" switch. What the OP is proposing is in the event of an outage the HO rolls out a portable unit, connects it to the house, starts generator and the ATS transfer with out him stumbling around in a dark basement.
The way to accomplish this would be to install ether a 240/24 or 120/24 transformer in the ATS connecting the primary Leads to the E1 E2 or E1 N lugs to get voltage to the transformer when the generator is running and send the 24v to the relay on 194 and 23.
As most have said it is simpler to set a sub panel and have a DT switch out side. You are going to be out there anyway with the generator. Crank gen., throw switch, go back inside.
 

iwire

Moderator
Staff member
Location
Massachusetts
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