# Generator: 200 amp ATS, 100amp main



## ctsparky (Dec 4, 2013)

Customer bought a package deal with a 200 amp service rated ATS with 17kw standby generator.

Can the existing service from "service point to meter to 100amp service conductors be installed into the ATS? Can a 1/0 SER be used from ATS to the 100amp electrical panel? (separating the grounds and neutrals), and leaving the current electrodes (ground rods and water meter bond).

Or is there a code reference that states that everything needs to be upgraded...

any code references would be great.


----------



## ElectricJoeNJ (Feb 24, 2011)

ctsparky said:


> Customer bought a package deal with a 200 amp service rated ATS with 17kw standby generator.
> 
> Can the existing service from "service point to meter to 100amp service conductors be installed into the ATS? Can a 1/0 SER be used from ATS to the 100amp electrical panel? (separating the grounds and neutrals), and leaving the current electrodes (ground rods and water meter bond).
> 
> ...


You have to do a service upgrade. The main breaker in the ats is going to be a 200. Unless you can change the breaker to a 100 you will have to upgrade the service. 

310.15(B)(7)


----------



## ctsparky (Dec 4, 2013)

Am I missing something in 310.15b7 that states that? call me an idiot, but a little help would be nice.


----------



## ElectricJoeNJ (Feb 24, 2011)

ctsparky said:


> Am I missing something in 310.15b7 that states that? call me an idiot, but a little help would be nice.


That code states what wire size you need for a 200 amp service. IF that transfer switch has a 200 amp breaker in it than all your wire must be sized to that Article.


----------



## Pharon (Jan 20, 2014)

If the generator is only 17kW, why is the ATS rated for 200A? Assuming it's a 120/240V, single phase service, as long as you have a generator OCPD rated for 100A, you should be fine. Doesn't matter if the ATS is rated higher.


----------



## jarhead0531 (Jun 1, 2010)

You have to size the wire to the breaker, so you would need 2/0 copper or 4/0 aluminum. That can feed the 100 main in existing panel as long as the lugs will support it, or possibly you would need a reducing crimp. The main breaker in ATS is only protecting the wire to the new panel.

Either way he was a dumb ass for ordering a 200A ATS for a 100 service. Generac makes 100, 150, and 200A models.

The crappy part is that you now have to upgrade the grounding. The grounding requirements are based on wire size, not Amps.


----------



## ElectricJoeNJ (Feb 24, 2011)

Pharon said:


> If the generator is only 17kW, why is the ATS rated for 200A? Assuming it's a 120/240V, single phase service, as long as you have a generator OCPD rated for 100A, you should be fine. Doesn't matter if the ATS is rated higher.


Incorrect. The ATS is sized for the service it is connecting too. There will also be a breaker in it for the generator, that has nothing to do with the service rated size of the switch.


----------



## ctsparky (Dec 4, 2013)

jarhead0531 said:


> You have to size the wire to the breaker, so you would need 2/0 copper or 4/0 aluminum. That can feed the 100 main in existing panel as long as the lugs will support it, or possibly you would need a reducing crimp. The main breaker in ATS is only protecting the wire to the new panel.
> 
> So even though there is only a 100 amp meter can on the outside of the house, because the ATS states it is 200 amp, everything up river and down river from that ATS has to be upgraded to 200 amps. why if only 100 amps is coming into the house?


----------



## ElectricJoeNJ (Feb 24, 2011)

Because everything is now protected by 200 amp breaker. It's the same difference as putting a 200 amp panel in if the service is only 100 amps. Your 100 amp service conductors are now protected by a 200 amp main. Your only other option is to put a 100 amp fused disconnect ahead of the ATS but at that point you mind as well upgrade the service. More money for you unless you bid the job wrong originally.
You seem to be missing the point that not only does the ATS STATE 200 amps, it HAS a 200 amp breaker in it.


----------



## Going_Commando (Oct 1, 2011)

Pharon said:


> If the generator is only 17kW, why is the ATS rated for 200A? Assuming it's a 120/240V, single phase service, as long as you have a generator OCPD rated for 100A, you should be fine. Doesn't matter if the ATS is rated higher.


The generator is sized to the calculated load, and the breaker is sized for the service rating. You can have a calculated load of 40A and have an 800A entrance if you really wanted to.


----------



## ctsparky (Dec 4, 2013)

yes it took me a little while to catch on, but I do understand, thanks for helping me understand.


----------



## Sparky J (May 17, 2011)

Had one a little while ago customer had a 20kw package deal with a 200a SE rated transfer switch. He did not want the whole service backed up so we put a 100a sub panel with his selected circuits in it.
But yes in your situation you would need a 100 amp disconnect before the 200 amp transfer switch, then it's just a switch.


----------



## Pharon (Jan 20, 2014)

ElectricJoeNJ said:


> You seem to be missing the point that not only does the ATS STATE 200 amps,* it HAS a 200 amp breaker in it.*


Where did he say that?

There's nothing in the Code that prevents a 200A ATS being fed by two 100A sources.

Like I said before, as long as the OCPD on both the generator side and the utility side are sized for 100A, he should be fine.


----------



## ctsparky (Dec 4, 2013)

I guess that is where I am confused is the code.... where does it say I can't use a 200 amp ats with a 100 amp service. 

The service entrance conductors from the service point down to the meter, and the meter can itself are all rated for 100 amps, if I install a 400 amp breaker in the ats, everything in front of ATS is still only 100 amps.....


----------



## ElectricJoeNJ (Feb 24, 2011)

Pharon said:


> Where did he say that?
> 
> There's nothing in the Code that prevents a 200A ATS being fed by two 100A sources.
> 
> Like I said before, as long as the OCPD on both the generator side and the utility side are sized for 100A, he should be fine.


I hope your not licensed and never get licensed. He has a 200 amp ats which has a 200 amp main breaker on the UTILITY side. Forget about the generator and the ocpd for a sec because you are only confusing yourself. Because of the 200 amp MAIN breaker everything going in and coming out of that switch (except the generator wiring) has to be sized for 200 amps. Got it??


----------



## ElectricJoeNJ (Feb 24, 2011)

ctsparky said:


> I guess that is where I am confused is the code.... where does it say I can't use a 200 amp ats with a 100 amp service.
> 
> The service entrance conductors from the service point down to the meter, and the meter can itself are all rated for 100 amps, if I install a 400 amp breaker in the ats, everything in front of ATS is still only 100 amps.....


You can't feed a breaker with wiring that's rated for less then the breaker is rated. Basic stuff here.


----------



## Pharon (Jan 20, 2014)

I think you need a serious lesson in reading comprehension. There's nothing that he's posted that says ANYTHING about 200A OCPD's on either the utility or the generator side.

You could have a 100A generator CB and a 100A service disconnect CB feeding an 800A ATS and still be compliant.

Basic stuff here.


----------



## ElectricJoeNJ (Feb 24, 2011)

Pharon said:


> I think you need a serious lesson in reading comprehension. There's nothing that he's posted that says ANYTHING about 200A OCPD's on either the utility or the generator side.
> 
> You could have a 100A generator CB and a 100A service disconnect CB feeding an 800A ATS and still be compliant.
> 
> Basic stuff here.


Omg. Yup your definitely an engineer. It's a 200 amp service rated ATS IT HAS A 200 AMP MAIN BREAKER IN IT. ON THE UTILITY LINE SIDE. can you f-ing read. Post # 1 first sentence.


----------



## Sparky J (May 17, 2011)

The switch could have a 5000000000 amp breaker on it it makes no difference if you have a 200 amp breaker ahead of it then it's just a switch (a very expensive one).
This also depends upon the AHJ some may not allow it for reasons I do not know.


----------



## Pharon (Jan 20, 2014)

Exactly. The rating of the ATS itself doesn't matter as long as the upstream OCPD on both sides is 100A. If not, then either change out the breakers or upsize the service to 200A. It's not rocket science.


----------



## ElectricJoeNJ (Feb 24, 2011)

Pharon said:


> Exactly. The rating of the ATS itself doesn't matter as long as the upstream OCPD on both sides is 100A. If not, then either change out the breakers or upsize the service to 200A. It's not rocket science.


Now all of the sudden you see the point but change the wording to make it seem like your idea. Your ridiculous. The particular ATS he is using has a 200 amp breaker in it. It is meant to be installed in between the meter and the main panel. Doing so makes the ATS the new service main disconnect and all wires feeding it must be sized accordingly. There is no OCPD ahead of the switch and the downstream OCPD no longer serves a purpose.


----------



## ElectricJoeNJ (Feb 24, 2011)

Sparky J said:


> The switch could have a 5000000000 amp breaker on it it makes no difference if you have a 200 amp breaker ahead of it then it's just a switch (a very expensive one).
> This also depends upon the AHJ some may not allow it for reasons I do not know.


There isn't any OCPD ahead of the switch. The switch is the services OCPD


----------



## Pharon (Jan 20, 2014)

ElectricJoeNJ said:


> Now all of the sudden you see the point but change the wording to make it seem like your idea. Your ridiculous. The particular ATS he is using has a 200 amp breaker in it. It is meant to be installed in between the meter and the main panel. Doing so makes the ATS the new service main disconnect and all wires feeding it must be sized accordingly. There is no OCPD ahead of the switch and the downstream OCPD no longer serves a purpose.


I don't know what you've been reading but I've been saying the exact same thing since the start of this thread. Not all service rated transfer switches have built in OCPDs on their mains, though if all you've ever done is resi I could see how you might not know that.

You may also want to consider switching to decalf - you seem a little bit tense, bro.


----------



## nrp3 (Jan 24, 2009)

Ok. I'm intrigued, got an example of that?


----------



## ElectricJoeNJ (Feb 24, 2011)

Pharon said:


> I don't know what you've been reading but I've been saying the exact same thing since the start of this thread. Not all service rated transfer switches have built in OCPDs on their mains, though if all you've ever done is resi I could see how you might not know that.
> 
> You may also want to consider switching to decalf - you seem a little bit tense, bro.


No no no. You haven't been saying the same thing as me. Show me a service rated switch that doesn't have a main breaker in it. And I guarantee I'm a more well rounded electrician then you can ever hope to be.


----------



## Pharon (Jan 20, 2014)

nrp3 said:


> Ok. I'm intrigued, got an example of that?


My apologies, you're correct. A service entrance rated switch by definition means that it must include a service rated main OCPD. My mistake. Most of the ATS's I deal with are 400A and larger, and none of them have built in mains, so when I see the term ATS, to me it means only the switch itself and no OCPD. In re-reading the first post I see that he meant to land the service cables directly into the ATS - I thought he was going from an existing main service disconnect into the ATS.

I apologize for the misunderstanding and this will be my last post in this thread.


----------



## ElectricJoeNJ (Feb 24, 2011)

Pharon said:


> My apologies, you're correct. A service entrance rated switch by definition means that it must include a service rated main OCPD. My mistake. Most of the ATS's I deal with are 400A and larger, and none of them have built in mains, so when I see the term ATS, to me it means only the switch itself and no OCPD. In re-reading the first post I see that he meant to land the service cables directly into the ATS - I thought he was going from an existing main service disconnect into the ATS.
> 
> I apologize for the misunderstanding and this will be my last post in this thread.


Accepted. We all make mistakes which is why I was pushing the issue. The op needed correct advice on this not misinformation.


----------



## Sparky J (May 17, 2011)

ElectricJoeNJ said:


> There isn't any OCPD ahead of the switch. The switch is the services OCPD


Understood, I am saying that the OP could use the customers transfer switch with a 100 amp OCPD ahead of it. Stupid and costly yes but customer already has it. Or they could sell it and get the 100 amp ATS for the existing service.


----------



## ElectricJoeNJ (Feb 24, 2011)

Sparky J said:


> Understood, I am saying that the OP could use the customers transfer switch with a 100 amp OCPD ahead of it. Stupid and costly yes but customer already has it. Or they could sell it and get the 100 amp ATS for the existing service.


Unfortunately they don't offer that generator with a 100 amp transfer switch unless its the 16 circuit transfer panel type switch.


----------



## ceb58 (Feb 14, 2009)

Sparky J said:


> Understood, I am saying that the OP could use the customers transfer switch with a 100 amp OCPD ahead of it. Stupid and costly yes but customer already has it. Or they could sell it and get the 100 amp ATS for the existing service.


I do not see a big cost. I just bought a 100amp nema 3 with the 100 amp breaker in it for less than $50.00 at Lowes. Price would be a lot less than a service up grade.


----------



## jarhead0531 (Jun 1, 2010)

ElectricJoeNJ said:


> Unfortunately they don't offer that generator with a 100 amp transfer switch unless its the 16 circuit transfer panel type switch.


As a package, no, if you are a dealer you can order whatever you want with a generator. If you aren't a dealer, order them separately. Problem solved, why are we making this so frickin difficult. Oh wait, because we are electricians....


----------



## dronai (Apr 11, 2011)

Can't he just put a 100A disconnect between the Meter, and the ATS ?


----------



## ElectricJoeNJ (Feb 24, 2011)

dronai said:


> Can't he just put a 100A disconnect between the Meter, and the ATS ?


He sure can. I already suggested that


----------

