24kw Generac generator 200 amp Ats

[pmoney44]

Good day,

Customer just ordered a 24kw Generac generator and this will be my first install. They have a 200 amp service. The generator has a 100 amp main breaker but the ATS is 200 amps. I’m trying to order my wire but am a bit confused on sizing. House service fed underground with 4/0 aluminum. Utility wire a lot smaller than that. Can’t read actual size but. I’m wondering what size wire for everything. (IE) transfer switch and generator for correct sizing. Other than a well pump, electric dryer, 40 amp ac unit, I see are the only big draw.
Thanks in Advance!!!

 

[Dennis Alwon]

You do know with an ATS and no load shedding the generated must be able to serve the entire load on the panel. Just imagine what good it does if you keep tripping the 100 amp breaker.

Don't worry about the utility as they have their own rules for sizing the service. You need a 200 amp transfer switch and 4/0 to the house 200 amp panel. From the ATS to the generator you need a wire sized for the generator 100 amp capacity

 

[zooby]

morning...i am not one of the "big brains" on here but just a thought.....unless you are being told to plan for future upsize, wouldnt you size to the 100a generator? The 200 at the ATS is what i is rated for ...right? are you backing up the whole panel or setting an "E" panel? Good things to ya.

 

[zooby]

You do know with an ATS and no load shedding the generated must be able to serve the entire load on the panel. Just imagine what good it does if you keep tripping the 100 amp breaker.

Don't worry about the utility as they have their own rules for sizing the service. You need a 200 amp transfer switch and 4/0 to the house 200 amp panel. From the ATS to the generator you need a wire sized for the generator 100 amp capacity

Morning....Dennis i am just seeing if i was in the ballpark-----is the load shed you mentioned achieved with a "E" panel ( only certain loads?) Thanks

 

[Dennis Alwon]

I haven't done a generator in 15 years. I believe that some generators have the ability to load shed but I don't know how it is done. I am sure someone will know

 

[Doc13067]

Load shedding is achieved by modules for each circuit that you need delayed. Those modules need to be connected near the origin of the circuit you intend to delay. At least this is the case with Generac. You should have if you’re using aluminum 4/0-4/0-2/0 from the meter to the ATS, 4/0-4/0-4/0-2/0 from the ATS to the load center (remember to convert load center to a sub panel) and 2-2-2-6 from the generator to the ATS. I have never seen a residential install where the generator breaker is the same size as the load center breaker. It will be fine as you described it just put load shedding on the big items.

 

[kwired]

I haven't done a generator in 15 years. I believe that some generators have the ability to load shed but I don't know how it is done. I am sure someone will know

All the Generac's I seen in recent years have 4 load shed relays standard incorporated to the ATS. Not too long ago I think you had to add on equipment for load shedding abilities.

What they have is set up for easily breaking the 24V control of HVAC equipment. For other shedding other items you might need additional relays/contactors though.

They typically work by monitoring change in frequency to trigger the load shedding. More load you have on the generator will cause drop in frequency. If load drops it will allow the shed item to come back on line as long as frequency doesn't drop too much afterward.

 

[kwired]

morning...i am not one of the "big brains" on here but just a thought.....unless you are being told to plan for future upsize, wouldnt you size to the 100a generator? The 200 at the ATS is what i is rated for ...right? are you backing up the whole panel or setting an "E" panel? Good things to ya.

Dennis is right in that with an ATS the generator needs to be able to handle the connected load, or only transfer fixed amount of loads, or have load shedding abilities. Just because you have 200 amp service does not mean you have 200 amps of load though. Do a load calculation , if it ends up under 100 amps then the generator should be fine without using any load shedding features.

If you have 200 amp service conductor and 200 amp conductor to the main panel, then the 200 amp main in the ATS is fine for protecting those.

If the generator has a 100 amp output breaker, there is no reason other than voltage drop if generator is long distance away to run any more than 100 amp conductor between generator and transfer switch. The 100 amp breaker will trip if there is more than 100 amps of load, or depending on settings of generator controls, the unit may shut down before the breaker ever trips if loaded that heavily anyway. Just had problems with this recently where a unit had some parameters in the genset controller were all messed up, and it was shutting down on an overload error code even though it was lightly loaded.

 

[electrofelon]

. From the ATS to the generator you need a wire sized for the generator 100 amp capacity

Just to nitpick a bit, I don't see any requirement in article 445 to size the generator feeder to the breaker. It appears that 445.13 requires them be sized to 115% of the nameplate current rating of the generator. Probably pretty much or same result though.

 

[Doc13067]

All the Generac's I seen in recent years have 4 load shed relays standard incorporated to the ATS. Not too long ago I think you had to add on equipment for load shedding abilities.

What they have is set up for easily breaking the 24V control of HVAC equipment. For other shedding other items you might need additional relays/contactors though.

They typically work by monitoring change in frequency to trigger the load shedding. More load you have on the generator will cause drop in frequency. If load drops it will allow the shed item to come back on line as long as frequency doesn't drop too much afterward.

Wouldn’t you need to get some additional wiring from the circuit to the ATS for that to work? I recently was faced with this and found it easier to just interrupt the branch circuits with a module and not have to run any wires through the exterior wall for the ATS to use to delay the circuit

 

[kwired]

Just to nitpick a bit, I don't see any requirement in article 445 to size the generator feeder to the breaker. It appears that 445.13 requires them be sized to 115% of the nameplate current rating of the generator. Probably pretty much or same result though.

Would that apply to the 100 amp breaker in these packaged standby systems like in OP though?

I'm thinking it would be more for a situation where there is no OCPD in the generator unit and the first device is a field installed OCPD.

I connected a 26 kW unit recently. It came with 110 amp breaker installed in it. I ran 1/0 aluminum conductors. Guess I'd have to double check what rated amps was as PF needs to be considered as well, but not sure if this thing would have taken 2/0 conductor. Lugs likely big enough but bending room was not that great even for the 1/0.

 

[electrofelon]

Would that apply to the 100 amp breaker in these packaged standby systems like in OP though?

I'm thinking it would be more for a situation where there is no OCPD in the generator unit and the first device is a field installed OCPD.

I connected a 26 kW unit recently. It came with 110 amp breaker installed in it. I ran 1/0 aluminum conductors. Guess I'd have to double check what rated amps was as PF needs to be considered as well, but not sure if this thing would have taken 2/0 conductor. Lugs likely big enough but bending room was not that great even for the 1/0.

I guess it is somewhat open to interpretation:

445.13 Ampacity of Conductors.
(A) General. The ampacity of the conductors from the gener‐
ator output terminals to the first distribution device(s) contain‐
ing overcurrent protection shall not be less than 115 percent of
the nameplate current rating of the generator. It shall be
permitted to size the neutral conductors in accordance with
220.61. Conductors that must carry ground-fault currents shall
not be smaller than required by 250.30(A). Neutral conductors
of dc generators that must carry ground-fault currents shall not
be smaller than the minimum required size of the largest
conductor.

I guess we would need a more specific definition of "generator output terminals" and "first distribution device containing over current protection"

 

[kwired]

I guess it is somewhat open to interpretation:

445.13 Ampacity of Conductors.
(A) General. The ampacity of the conductors from the gener‐
ator output terminals to the first distribution device(s) contain‐
ing overcurrent protection shall not be less than 115 percent of
the nameplate current rating of the generator. It shall be
permitted to size the neutral conductors in accordance with
220.61. Conductors that must carry ground-fault currents shall
not be smaller than required by 250.30(A). Neutral conductors
of dc generators that must carry ground-fault currents shall not
be smaller than the minimum required size of the largest
conductor.

I guess we would need a more specific definition of "generator output terminals" and "first distribution device containing over current protection"

The unit breakers in Generacs I believe are Siemens Q series.

I hooked up a Cummins unit recently and it had a Square D QO unit breaker.

Both those breaker types are probably internally same build as typical Q series or QO series breakers and are rated for 80% continuous, 100% non continuous. I really see no reason theory wise to have different protection or ampacity requirement on the downstream conductor than the general protection rules. Between the alternator and the breaker, particularly if not factory supplied/installed on the unit, may be some good reasons for diffferent size or protection level.

I can tell you on both those I mentioned above that I just connected in the past couple weeks the factory installed conductors from the alternator were smaller than my field installed load conductors. But also looked like either nickel or tin plated conductors and likely higher temp insulation as well, but was also apart of the listed unit.

 

[qcroanoke]

I guess it is somewhat open to interpretation:

445.13 Ampacity of Conductors.
(A) General. The ampacity of the conductors from the gener‐
ator output terminals to the first distribution device(s) contain‐
ing overcurrent protection shall not be less than 115 percent of
the nameplate current rating of the generator. It shall be
permitted to size the neutral conductors in accordance with
220.61. Conductors that must carry ground-fault currents shall
not be smaller than required by 250.30(A). Neutral conductors
of dc generators that must carry ground-fault currents shall not
be smaller than the minimum required size of the largest
conductor.

I guess we would need a more specific definition of "generator output terminals" and "first distribution device containing over current protection"

Has this changed since 2014? A mike holt video calls it windings not terminals.

 

[pmoney44]

It does have AC shedding and I’m doing the whole house.

 

[pmoney44]

Load shedding is achieved by modules for each circuit that you need delayed. Those modules need to be connected near the origin of the circuit you intend to delay. At least this is the case with Generac. You should have if you’re using aluminum 4/0-4/0-2/0 from the meter to the ATS, 4/0-4/0-4/0-2/0 from the ATS to the load center (remember to convert load center to a sub panel) and 2-2-2-6 from the generator to the ATS. I have never seen a residential install where the generator breaker is the same size as the load center breaker. It will be fine as you described it just put load shedding on the big items.

Thanks very much!!

 

[Chamuit]

Do the load calc so you know exactly what you are dealing with.

Meter -> ATS->Load Center use your 4/0-4/0-2/0 aluminum

Gen->ATS use the 2-2-2-6

Forget adding an emergency panel. Use Smart Management Modules to handle the three large loads. Lock them out or let the SMMs shed the loads when too much.
G007000-0 for 50 amp
G007006-0 for 51-100 amp

 

[Hv&Lv]

You do know with an ATS and no load shedding the generated must be able to serve the entire load on the panel. Just imagine what good it does if you keep tripping the 100 amp breaker.

Don't worry about the utility as they have their own rules for sizing the service. You need a 200 amp transfer switch and 4/0 to the house 200 amp panel. From the ATS to the generator you need a wire sized for the generator 100 amp capacity

question here…
Say you get load data per 220.87 and the peak demand is 18kW.
Wouldn't the 24kW be sufficient without load shedding?

just because its a 200 amp service doesn't mean it will ever see 200 amps.
The disconnect is rated for 200 amps.

 

[LarryFine]

You have to account for all loads that could theoretically be left on with nobody home.

HVAC is probably the greatest concern; loads like a clothes dryer won't restart by itself.

 

[kwired]

You have to account for all loads that could theoretically be left on with nobody home.

HVAC is probably the greatest concern; loads like a clothes dryer won't restart by itself.

The dryers of the past typically would not restart, some modern ones possibly can, though I'd guess most won't after a power failure. Same is true for many modern washers, microwave ovens, dishwashers, and ovens. Even more likely with those mentioned items if they have electronic controls vs mechanical controls.

NEC doesn't really mention this sort of thing specifically but as worded I still think you are allowed to take this into consideration on what load will be automatically transferred.