Where to connect grid tied solar - Generator, 2 ATS, and 2 Inverters

**oregon_phil** · 09-30-2022, 04:08 PM

I have a Kohler generator and solar.

If you have access to your meter base panel, please get the part number and take pictures of what's inside. I am assuming this is a meter base with breakers in it but meter base part number and pictures would help. Please be careful.

Your schematic doesn't show how everything is connected.

**Mr. Inquisitive** · 09-30-2022, 10:46 PM

The main panel is a Square D SU3040D400CB 400A panel. I will have to post the wiring behind the cover later but here is the breaker layout.
Main Panel 1.jpg

The schematic I previously provided is just the generic schematic from Generac for the ATS. The wires entering the first ATS on the top are from the main panel. Unfortunately, the equipment was all installed before my daughter bought the home and no documentation is on file with the county (according to the county, which is hard to believe) and we don't know who installed it. All I have is what is shown. I will likely have to tone out lines to verify connections since the sub panels are 100+ feet from the main.

**DanS26** · 10-02-2022, 10:24 AM

Does the garage have to have backup power? If not, eliminate the second ATS and repurpose the garage wiring to connect to the utility supply side. Then attach the inverters to the garage subpanel. No digging and no extra wire.

**Mr. Inquisitive** · 10-02-2022, 02:07 PM

Hi Dan. Yes the garage does need backup power as it is used as a living space occasionally (full bathroom, etc.).

**DanS26** · 10-02-2022, 06:39 PM

Well then I would suggest to run high voltage DC to string inverter mounted next to the main panel. Less wire cost for the 300' run.

Good luck!

**oregon_phil** · 10-02-2022, 06:51 PM

Originally posted by Mr. Inquisitive

The main panel is a Square D SU3040D400CB 400A panel. I will have to post the wiring behind the cover later but here is the breaker layout.
Main Panel 1.jpg

The schematic I previously provided is just the generic schematic from Generac for the ATS. The wires entering the first ATS on the top are from the main panel. Unfortunately, the equipment was all installed before my daughter bought the home and no documentation is on file with the county (according to the county, which is hard to believe) and we don't know who installed it. All I have is what is shown. I will likely have to tone out lines to verify connections since the sub panels are 100+ feet from the main.

I am not an electrician nor a EE so take anything I say with a grain of salt. I am a retired ME with design and process experience.

I think this is your setup. You can confirm it when you are on site.

My generator only has one transfer switch and it is wired up exactly like xfer switch 2. My solar is connected to the same breaker panel box as the 125 amp garage breaker. When the power goes out, solar goes off line, then my transfer switch transfer power from the generator to my house panel.

Hooking up one inverter would be pretty easy, but you can't put two inverters on the meter breaker panel because of NEC 120% rules. The other inverter probably needs to go after the house disconnect switch but before the utility connection on transfer switch 1.

But remember I'm an ME and you should talk to an electrician for sure. I just like to untangle seemingly messy issues if I can help.

Good luck!

Attached Files

Two ATS.pdf (428.2 KB, 3 views)

**Mr. Inquisitive** · 10-03-2022, 06:19 AM

Originally posted by oregon_phil

Hooking up one inverter would be pretty easy, but you can't put two inverters on the meter breaker panel because of NEC 120% rules.

I am not sure if this is the case. The main panel is a 400A panel. The inverters are 7.6kW inverters. would that really exceed 120%? Or am I misunderstanding what you are saying?

**Mr. Inquisitive** · 10-03-2022, 06:21 AM

Originally posted by DanS26

Well then I would suggest to run high voltage DC to string inverter mounted next to the main panel. Less wire cost for the 300' run.

I will have to give this some thought. It is 2 inverters so I think I would need to run 2 sets of DC vs 1 set of AC if I put the inverters at the garage. I don't intend to go over 14kW total in the long term so this should be doable on a single AC run.

**DanS26** · 10-03-2022, 10:30 AM

Originally posted by Mr. Inquisitive

I will have to give this some thought. It is 2 inverters so I think I would need to run 2 sets of DC vs 1 set of AC if I put the inverters at the garage. I don't intend to go over 14kW total in the long term so this should be doable on a single AC run.

Yes....4 wires of large diameter of aluminum or 4 wires of slightly smaller copper for AC vs 5 wires of smaller diameter copper for DC. Voltage loss caclculation will be very important.

**oregon_phil** · 10-03-2022, 11:05 AM

Originally posted by Mr. Inquisitive

I am not sure if this is the case. The main panel is a 400A panel. The inverters are 7.6kW inverters. would that really exceed 120%? Or am I misunderstanding what you are saying?

To clarify, the meter base is connected to the house 200 amp service disconnect and garage 200 amp service disconnect. The garage 200amp service disconnect is connected to 30 space/40 circuit breaker panel with 200 amp buss bars (assumed, doesn't specifically say). You can connect one inverter to buss bars. But there might be other ways to do what you want. Best talk to an electrician.

**oregon_phil** · 10-03-2022, 03:21 PM

Originally posted by Mr. Inquisitive

I will have to give this some thought. It is 2 inverters so I think I would need to run 2 sets of DC vs 1 set of AC if I put the inverters at the garage. I don't intend to go over 14kW total in the long term so this should be doable on a single AC run.

I read this to say you would run an additional set of AC lines for the inverters.

Questions to help you figure out the details:

1) How do you combine two inverters at the garage?
2) Two 7.7 inverters is 80 amps worth of breakers at the meter breaker panel. You have a 200 amp service disconnect at the meter base for the garage unit. What does the service disconnect need to be decreased to in order to fulfill the 120% rule? Does this set up still work?

**DanS26** · 10-03-2022, 05:28 PM

The new and additional garage main breaker will have to be derated to 150 amps. Two 40 amp breakers installed at the bottom of the garage panel accepting load from each inverter. Make sure AHJ is OK with this since some jurisdictions require a blade disconnect instead of breakers. Remember this new garage panel cannot interact with the existing garage panel.

IMO I would not go this route.....instead run 5 wires of high voltage DC to inverters at the 400 amp load center 300ft away.

**Mike 134** · 10-03-2022, 05:48 PM

I see Oregon Phil listed his profession so the OP could have an idea about his skill set. How about the rest of you just handymen putzing with electrician stuff?
Myself 38 years feeding my family as a journeyman electrician, you might have noticed I didn't offer advice, to many unknows in a forum post.

**DanS26** · 10-03-2022, 06:05 PM

Originally posted by Mike 134

I see Oregon Phil listed his profession so the OP could have an idea about his skill set. How about the rest of you just handymen putzing with electrician stuff?
Myself 38 years feeding my family as a journeyman electrician, you might have noticed I didn't offer advice, to many unknows in a forum post.

Mike, there are parts of the country that the NEC is just a suggestion. No inspections, no nothing.....if your house burns down that is your problem.

Where to connect grid tied solar - Generator, 2 ATS, and 2 Inverters

Where to connect grid tied solar - Generator, 2 ATS, and 2 Inverters

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