Generator ATS Question

[mkgrady]

I have been doing a fair amount of home standby generator installs lately but I'm not sure how to do this one. Normally I will calculate the size generator required, put in a smart service rated ATS to control AC systems and use contactors to control heavy loads like ovens and dryers. In every case I wind up putting in a 10-20KW generator and either a 100 or 200 amp ATS.

On this job the service is rated 300 amp. probably because he has so many big woodworking power tools. If it were not for that a 200 amp service would have been the right size and most likely a 20KW generator would have been the right size. I'm thinking I could put the wood shop on a contactor that would be controlled by the smart ATS

The 300 amp service meter feeds a 200 amp panel that feeds most of the house and the meter also feeds a 100 amp panel that feeds a smaller portion of the house but the part they use the most. So both panels must be powered by the generator.

I'm trying to figure out what the ATS should be. I don't think a 300 amp ATS is made. Is my only choice to use a 400 amp service rated ATS and use the smart features to limit the load on the generator? I'm thinking yes but hoping for other suggestions because I imagine a 400 ATS is very large and space is limited.

 

[ATSman]

GE-Zenith ATS

GE-Zenith ATS

I have been doing a fair amount of home standby generator installs lately but I'm not sure how to do this one. Normally I will calculate the size generator required, put in a smart service rated ATS to control AC systems and use contactors to control heavy loads like ovens and dryers. In every case I wind up putting in a 10-20KW generator and either a 100 or 200 amp ATS.

On this job the service is rated 300 amp. probably because he has so many big woodworking power tools. If it were not for that a 200 amp service would have been the right size and most likely a 20KW generator would have been the right size. I'm thinking I could put the wood shop on a contactor that would be controlled by the smart ATS

The 300 amp service meter feeds a 200 amp panel that feeds most of the house and the meter also feeds a 100 amp panel that feeds a smaller portion of the house but the part they use the most. So both panels must be powered by the generator.

I'm trying to figure out what the ATS should be. I don't think a 300 amp ATS is made. Is my only choice to use a 400 amp service rated ATS and use the smart features to limit the load on the generator? I'm thinking yes but hoping for other suggestions because I imagine a 400 ATS is very large and space is limited.

One suggestion I could make is :
Hook up a recording ammeter to record the usage for a period of 1 week. If the total load is under 260A then
GE-Zenith Controls makes a 260A ATS in the ZTG model. The smart controller (MX150) can be programmed to activate the load disconnect feature. This could send a signal to disconnect the wood shop (non-essential load) through a contactor whenever the the generator starts and the ATS transfers to emergency.

 

[mkgrady]

One suggestion I could make is :
Hook up a recording ammeter to record the usage for a period of 1 week. If the total load is under 260A then
GE-Zenith Controls makes a 260A ATS in the ZTG model. The smart controller (MX150) can be programmed to activate the load disconnect feature. This could send a signal to disconnect the wood shop (non-essential load) through a contactor whenever the the generator starts and the ATS transfers to emergency.

Thanks for the suggestion but the house is and will be unoccupied for several weeks. When the owner gets back they want it up and running. If I could conclude the the above ATS was large enough for the load during an outage with load shedding, it is still smaller than the 300 amp service so I assume I would limit there available 300 amp service during normal power.

The contractor that hired me to wire this only installs Generac generators. Does the Zenith even work on a Generac?

 

[hurk27]

Thanks for the suggestion but the house is and will be unoccupied for several weeks. When the owner gets back they want it up and running. If I could conclude the the above ATS was large enough for the load during an outage with load shedding, it is still smaller than the 300 amp service so I assume I would limit there available 300 amp service during normal power.

The contractor that hired me to wire this only installs Generac generators. Does the Zenith even work on a Generac?

No Generac ATS are dumb ATS all the controls for it are in the generator and they wont mix with other brands, if the meter is a 320 with dual lugs you could just use two transfer switch's maybe a 200 and a 100 for each panel, also make sure the generator will handle the loads as you do not want to transfer into an overload you might have to use a 35kw or a 45kw as a 20kw is only 83 amps, Generac has instructions to use ganged transfer switch's, I have never installed them but was told that they have this option.

Also I hope these two panels are grouped as per 230.72? or you might have another problem to deal with when you get your inspection, also as you should know these two panels will now become sub panels and grounding and bonding (I.E. separation of neutrals and grounding as well as the landing of the GEC's in the new transfer switch's) the 230.72 issue will go away if you install two ATS by the meter as they will now become your service disconnects.

If the panels are close to each other then you might be better off using another panel and bring the circuits you need to supply from the generator to this panel which you feed it from the ATS, but with an install like this you have some home work to do.

Also keep in mind that most home gas services are only 250 CFM and a fully loaded 20kw Generac requires at least 350 CFM of NG, 35kw and 45kw are even more, so make sure you will have adequate gas supply or the gas might have to be updated by the utility, if Propane then maybe just the regulator and or line from the tank will have to be up-sized.

One of the biggest mistakes some contractors do is not to take into account of the fuel supply, or they undersized the gas piping, Generac will void the warranty if this is found as it will lean burn the engine and can cause damage to it.

 

[mkgrady]

Thank you Hurk. Very informative. I passed on your gas supply issues to the GC who is a mechanical contractor.

Looking back at my initial thought I don't think I could use a 400 amp ATS because the service entrance lateral is only rated for 300 amps. Or would the existing two service panel breakers (200 and 100) serve that purpose. I'm confused because those two panels would no longer be service mains. They would be subpanel mains.

Anybody here ever use two ATS's on a single Generac? That seems like the way to go if it can be done. I'm still working on the generator size. Trying to get answers on how much of the customer load needs to run during an outage.

 

[mgookin]

Can't speak for Mass but in the FPL service area of FL we have to get ATS's blessed by the electric utility. It makes them a good source for technical advice.

 

[kbsparky]

....Anybody here ever use two ATS's on a single Generac? That seems like the way to go if it can be done. I'm still working on the generator size. Trying to get answers on how much of the customer load needs to run during an outage.

We recently worked on a job with 2 transfer switches: 100 Amp and 200 Amp. Either one could activate the generator set if its supply failed.

The gen set was a NG fired GENERAC 175 kVA unit, 3 phase, 480 Volts. That thing was almost as big as a car!

 

[mkgrady]

We recently worked on a job with 2 transfer switches: 100 Amp and 200 Amp. Either one could activate the generator set if its supply failed.

The gen set was a NG fired GENERAC 175 kVA unit, 3 phase, 480 Volts. That thing was almost as big as a car!

were the controls just wired in parallel?
Did you bring the generator output to a jb and spliced to each ats?

 

[kbsparky]

Controls consist of a simple 2-wire control line. Wired in parallel.

As for the output, the gen set had 2 breakers mounted on it: 100 Amp and 200 Amp. Ran individual lines all the way out to the unit, and connected them directly to those breakers.