120% rule, help!

[roofsolartexas]

I'm having an electrician build a new electrical system in my house. Right now, I have a new service entrance, meter can, main disconnect equipped with a 200 amp breaker, a 200 AMP main load center with 200 AMP breaker, and a 125 AMP sub panel which will have all my lights and outlets. The purpose of the sub panel is, when I get the Power Walls in the future, they just have to mount it in between and not have to worry about splicing wires.

I asked Tesla in the beginning, if I needed a solar ready panel. They said no, a 200 AMP panel was fine. I sent my electrician some questions and some articles pertaining to the 120% rule, either he didn't read them because he's older, and has his own ideas, or....I honestly don't know. He is very difficult to talk too and extremely defensive and short tempered.

I need to have my full 200 AMP capacity in my main panel. I'm attaching pictures below of my new set up, it's all permitted. I'm still pulling fresh wire and working on re-wiring inside my house. So nothing has been hooked into the panels yet. Which is why, I'm really trying to find out if I need to make changes right now so I don't lose capacity.

Option 1 would be to replace the meter can with a solar ready one. I've already got chewed by my electrician saying the local utility has to have this particular Milbank model. I just don't believe they would require a certain brand. I wanted a meter with a disconnect/breaker built in, he said "The power company doesn't want you messing with their meter." Umm, my breaker is separate from their sealed unit. I don't think I agree with that. I know there's ringless and ring type meter cans, that's it.

Option 2: I have a 200 AMP exterior disconnect box that is separate from the meter, which feeds the 200 AMP service panel which has it's own 200 AMP breaker. The article says that I can run power through here, but there are only two open lugs for neutrals, nothing for incoming hot waters from the solar inverter.

Option 3: I'm not sure if this was crystal clear, if mounting the breaker in the main 200 AMP panel, OPPOSITE end of the 200 AMP breaker, would be acceptable to allow me to keep my full 200 AMP capacity.

Option 4: Put the solar inverter breaker into the sub panel, but then I wouldn't be sure if I would have to down grade my 125 AMP 30(or 32)space GE sub panel.

Option 5: Install a solar ready 200 AMP panel.

I didn't include the other options, because I DO NOT want to down grade my breaker size on the main panel. It was my idea to have the service disconnect installed outside, and to have the sub panel installed.

Seimens sells a combo meter that is strictly a meter can and has provisions for the solar, that would be the simplest thing I would think. But then, I need to know if the utility would approve it. I'm having trouble believing my electrician since he loses his mind when I start talking about things that go against what he wants.

Tesla, the advisor I'm not even sure he knows 100%. Yes, my 200 AMP load center would work, but he left out the fact that I may have to down grade it, and it won't be a 200 AMP load center any more.

If anyone on here can help, that would be great. The last thing i want to do is have all the wiring pulled through and then have to change out the panel and it would cost more. My electrician says Seimens panels are garbage and I don't want one. GE doesn't make a solar ready panel, or anything solar ready from my searches.

No matter who is wrong, it is me that is going to be on the hook and having to pay extra to fix other peoples wrong answers and mistakes. I'm not an expert, I'm paying experts and quite frankly, information is lacking and my electrician is experienced, but very spoiled in his ways.

I just want a CLEAN install, I told him I would pay extra to do it right the first time and over build it. He balked at me when I asked about a 225 AMP panel, saying I would never need that much power. It wouldn't have cost much more to install it. If I were to do this over again, I would have had some changes made. This is the first time I've ever dealt with upgrading electrical, but I can say I've learned a lot. Thanks!

Article on 120% rule:

2014 NEC 705.12(D)(2) – Understanding PV Interconnections – Jade Learning

Literature from Seimens on solar ready panel:

https://www.downloads.siemens.com/d...aspx?pos=download&fct=getasset&id1=BTLV_48926

 

[roofsolartexas]

I would have edited this in there. I do not know what model solar inverter I will be getting. Yes, people have posted before, but that doesn't help because I don't know what the model is. If I have a 6 KW system, will they use a different version then someone with a 4 KW, or a 10 KW system?

As far as OPTION 3 goes, even with it on the opposite end, I still may have to down grade, and I don't want to.

I'm really close to calling another electrician and paying him to look at this and give an expert opinion. I've spent about $4,500.00 plus to get what you see done so far. I'm all about making sure this is done right the first time, I feel my electrician and Tesla are letting me down.

 

[sleevemedia]

Line-side tap?

Grid-tied Solar and the Dreaded 120% Rule | altE Solar Blog

 

[mongo]

If you are using the powerwalls for backup with a gateway, you can change the generation panel to a main breaker style and connect it and the 200a breakered load panel to the load side of the gateway which goes after the 200A main service breaker.

 

[BrettS]

I am not an electrician, so take this with a grain of salt, but if you are getting powerwalls I don’t believe that you need to worry about the 120% rule, so I think Tesla was right when they said you can just have a normal 200A panel.

It’s my understanding that the 120% rule comes into play when you are doing solar only. In that case you will have the breaker for your solar system in your main panel and it’s possible that your system could pull the full 200A from the grid as well as however much power the solar system can provide and overload your system. So you need to downsize the main breaker so that this can’t happen.

However, with powerwalls (at least in my installation) there is a totally separate ‘generation panel’ that has the breakers for the powerwalls as well as the inverters.

So in my case, my original main panel just has my 200A service disconnect breaker. That is connected to the gateway. There is a critical loads panel with all my breakers in it that’s also connected to the gateway, and finally the generation panel that has the powerwalls and inverters and that is connected to the gateway as well.

As far as your electrician goes, if he’s not listening to you and/or not doing what you want, then it definitely seems like it’s time to find another electrician.

 

[mongo]

I am not an electrician, so take this with a grain of salt, but if you are getting powerwalls I don’t believe that you need to worry about the 120% rule.

It’s my understanding that the 120% rule comes into play when you are doing solar only. In that case you will have the breaker for your solar system in your main panel and it’s possible that your system could pull the full 200A from the grid as well as however much power the solar system can provide and overload your system. So you need to downsize the main breaker so that this can’t happen.

However, with powerwalls (at least in my installation) there is a totally separate ‘generation panel’ that has the breakers for the powerwalls as well as the inverters.

So in my case, my original main panel just has my 200A service disconnect breaker. That is connected to the gateway. There is a critical loads panel with all my breakers in it that’s also connected to the gateway, and finally the generation panel that has the powerwalls and inverters and that is connected to the gateway as well.

You are describing what I have in my post. If the solar/ PW feed comes from outside the main panel, there is no need to uprate the bus bars. However, in the way OP has it, the connection to the main panel is via a back fed breaker, so the busbars can be fed by both the main 200A breaker and the generation break, potentially overloading them.


If the main service, generation panel, and load panel all have main breakers, and are connected at the junction between them, then no panel can be overloaded.

There is also the case where there is no solar and the gateway limits PW output to prevent overloading the busbars (load leveling situation), but that is probably not wide accepted since it relies on software.

@roofsolartexas, looking at your panel picture, for the 120% rule, the generation is supposed to connect at the further slot from the main, that reduces the max load on the busbar sections. If they are next to the main, then it can only be 100% rated.

 

[BrettS]

You are describing what I have in my post. If the solar/ PW feed comes from outside the main panel, there is no need to uprate the bus bars. However, in the way OP has it, the connection to the main panel is via a back fed breaker, so the busbars can be fed by both the main 200A breaker and the generation break, potentially overloading them.

That’s how it’s set up now, but when he gets his powerwalls the gateway will go between the main panel, his loads, and the generation panel, so I don’t believe that this will be a problem anymore.

 

[roofsolartexas]

Yes, as seen in the picture, power comes in this way:

1. Meter can
2. 200 amp service disconnect outside
3. Main panel with 200 amp disconnect inside
4. (Future use Tesla Gateway in middle of the main and sub)
5. 125 sub panel which has all 120 volt back up loads. It has around 30 slots and will probably have the hvac on there too.

As far as the service line tap, I’m not sure how they will do that. The disconnect only has empty spaces for a couple Neutral wires.

Right now, I’m thinking of holding off on the Tesla Powerwalls u til Elon makes his announcement in September. I don’t know if they would still install the power gateway or they would make me wait.
Thanks to all, I’ll write more but I have to get back to work.

 

[mongo]

That’s how it’s set up now, but when he gets his powerwalls the gateway will go between the main panel, his loads, and the generation panel, so I don’t believe that this will be a problem anymore.

Ahhhh
Thanks!

 

[charlesj]

... He is very difficult to talk too and extremely defensive and short tempered.

...

Such headaches. Is it too late to find a better suited electricians?

 

[roofsolartexas]

The reason I chose this electrician, he runs and owns the company, and lives half a mile away. Plus, he was okay with me running wiring myself. His prices were reasonable.

I did talk to Tesla today, they said I may or may not have a generation panel. I asked him to send me a diagram, and I got a diagram I already received, which was how I tried to design my new electrical set up.

I asked for pictures of installs with this generation panel, and haven’t received any. He did not say gateway. I made it clear I will not be able to down grade the 200 amp breaker. We need to figure out a different way, and that’s when he said generation panel. But then, he started talking about load calculations, I believe he was saying I may not need 200 amps and can down grade.

After I got off the phone, I got a diagram emailed from him, that doesn’t show the generation panel. So I’m still where I’m at before, and have no idea what they will do.

 

[roofsolartexas]

Line-side tap?

Grid-tied Solar and the Dreaded 120% Rule | altE Solar Blog

Thanks for the article. I read that, but I’m not sure how the line side tap would work. Specifically, how would they tap into the wires?

This is extremely confusing for me. The Tesla rep said that with a regeneration panel, it’s basically a box that has a breaker for the inverter and something else. It sounded like power would be routed from the supply lines from the meter to this box, then back to the 200 amp disconnect and then outside again?

he said I wouldn’t need a regeneration panel with my set up. Someone here mentioned the inverter output power would be fed straight into the gateway itself. Im not an electrician, I’m a very visual person.

below is a picture with doodling a to give an idea of what’s going on. thanks.

I explained to Tesla why I didn’t want to do a whole house back up on the main. If I get a pool pump, and an a/c system, or have an RV hooked up outside, I will over load the powerwalls and it will *sugar* down. Sure, you can turn stuff off, but that just not something I’m going to do.

I also wasn’t clear if power coming in from the meter would be routed to the gateway. I don’t know what the outputs are within the gateway. For example, is there a like out for the main load center, and a line out for the backed up loads on the sub panel?

I’m really not happy with this process from Tesla.

 

[BrettS]

I asked for pictures of installs with this generation panel, and haven’t received any.

If it helps, here is a picture of my panels. I have two inverters that are on the right of that window, not in the picture. They connect to the small panel in the lower right through the conduit coming up from the bottom. That panel just has two breakers in it, one for each inverter. From there it goes up to the solar disconnect, then to generation panel, which is to the left of the disconnect. The generation panel has a breaker for the inverters and one breaker each for my four powerwalls. The box to the left of the generation panel is my backed up loads panel (which has all of my circuits in it because my whole house is backed up), then the gateway is to the left of that. On the far left is the meter and my old main panel, which now just has the 200A service disconnect in it.

If you want more pictures or pictures of inside the panels, let me know and I can take some tomorrow.

 

[Patrick66]

The inverters and powerwalls need to tie in downstream of the gateway, so the sub-panel is your problem. The cleanest solution is to replace the 125A panel with 225A, keeping the breakers all the same size.

 

[BrettS]

The inverters and powerwalls need to tie in downstream of the gateway, so the sub-panel is your problem. The cleanest solution is to replace the 125A panel with 225A, keeping the breakers all the same size.

That’s a really good point. The 200 amp panel isn’t the problem at all here. If they don’t use a generation panel then they would need to add the powerwalls and inverters to the backup loads panel. That’s the panel that could potentially run into the 120% rule issue here.

 

[miimura]

My main panel has a 200A bus. It has a 125A breaker installed that feeds a sub-panel. When the Powerwalls were installed, the same 125A breaker was used to feed the Tesla Backup Gateway. The original subpanel and a new 200A bus Generation Panel were installed and fed by the backup side of the Gateway. I have some minor 120V loads in my Generation panel that were relocated from the main panel so that they would be backed up.

My point? If the OP's sub-panel has a 200A bus and is fed by a 125A breaker, I don't see the problem using it as the generation and backup loads panel. 125A grid breaker + 2X 30A Powerwall breakers + 10kW solar 50A breaker? That fits within the 120% rule doesn't it?

 

[Patrick66]

If the OP's sub-panel has a 200A bus and is fed by a 125A breaker, I don't see the problem using it as the generation and backup loads panel. 125A grid breaker + 2X 30A Powerwall breakers + 10kW solar 50A breaker? That fits within the 120% rule doesn't it?

Correct... but a standard sub-panel rated 125A would have 125A bus. The panel should be upgraded to 200/225A bus now, or you re-work to add a generation panel later.

 

[wwhitney]

What non-backedup loads do you want to have in the interior 200A panel?

Any panel that can get its power from more that one connection has to meet one of the NEC criteria in Article 705 to ensure that its bus can not be overloaded. The 120% rule is the most common criterion, but there are other options.

So if you put a breaker in the 200A panel for a feeder to the Backup Gateway, behind which are the backed up loads and the generation interconnection, that 200A panel can get power from both the on-site generation and the utility, and so it has to meet one of the criteria. Unless your generation totals less than 32A in inverter output current, the 120% rule will not work without downsizing the main breaker in that panel. The other rule is that the sum of the breakers, excluding the main breaker, not exceed the bus rating. So you could use a 125A breaker to the Backup Gateway, and then up to 75A of breakers for non-backed up loads.

A less restricted wiring arrangement would be this: from the exterior 200A disconnect, bring your 200A feeder to a splice point (could be within the Backup Gateway). From the splice point, run a 200A feeder to the 200A non-backed up panel, and a separate 200A feeder to the Backup Gateway. The splice could be done with 3-port Polaris-style connectors, for example. [Backup Gateway 2 already has a set of extra lugs in it that you can use for this wiring topology, so that would make it simple to do. I forget their rating.]

That way the Non-Backed Up Panel only gets power from a single connection, so as long it has a main breaker (required under this scenario), its bus can not be overloaded.

A similar strategy is often used for a generation panel and a backed up panel on the load side of the Backup Gateway. The gateway has two sets of load side lugs, so it is easy to run separate feeder segments to each panel. Then the backed up panel has only one connection with a source of power, so again as long as it has a main breaker (required), its bus can not be overloaded. And the generation panel (main breaker also required) typically qualifies under the "sum of breakers" rule.

Cheers, Wayne

 

[wwhitney]

BTW, there are also rules for protecting the feeder when the feeder has multiple sources of supply, that is the reason for all the connected panels to have main breakers. And there is a logical inconsistency in the NEC, as follows:

Say you have a 200A conductor (could be a busbar or a wire-type feeder) with (3) 200A circuit breakers connected to it, and no other connections. Then the conductor is protected for any combination of the (3) breakers being loads or supplies: If only (1) is a supply, no problem; if (2) are supplies, then there is only (1) 200A load breaker, so the conductor is protected that way.

The NEC allows this arrangement for feeders. But it does not allow this arrangement for busbars--a panel with a 200A main breaker and (2) 200A distribution breakers doesn't meet any of the criteria in Article 705. This inconsistency is the reason for the connection topologies described in my previous post. Plus that using the feeder interconnection saves physical space, since a splice box may be smaller than a panel, and the splices are often just made in the Backup Gateway itself.

Cheers, Wayne

 

[wwhitney]

PS. The upshot of all of the above is that you can leave the panels as is. When it comes time to install the Backup Gateway, put it to the right of the 200A panel, with a nipple between the two. Repull longer conductors from the exterior 200A disconnect, through your 200A interior panel, to the Backup Gateway. Run gateway-wise line side conductors back through the nipple to the existing 200A panel. Refeed the 125A interior panel from the load side of the Gateway. Add a generation panel also on the load side of the Gateway. If you have solar installed before hand in either the 200A or 125A interior panels, move the solar over to the generation panel.

PPS The Backup Gateway 2 also has provision for a small internal panelboard, which could take the place of the generation panel. So hopefully it will be available by the time you install Powerwalls, as it will simplify the feeder connections on both side of the gateway.

Cheers, Wayne