7.6 Kw Inverter with 100-amp Service

[josepr]

This is my first post. First, I would like to express my gratitude to all members of this forums. Your advice has been invaluable in times of need after being severely impacted by a category 4 hurricane. Using the information and advice from this forum I was able to successfully design and install a small off grid solar system. The system performed flawlessly. Mainly because, as advised, we had enough PV power and enough battery capacity (charged at 10% of C20 and never exceeded the 20% DOD level). Again, I want to thank all member for their time. Thank you!

In my jurisdiction an electrical installation does not have to be inspected but must be certified by a licensed electrician. We follow NEC 2017 but do not have a rapid shutdown requirement. My home has a 100-amp service (#2 AWG). The meter enclosure is the main panel. One 100-amp breaker. Ground and neutral are bonded in this panel. Four conductors run from this panel (3 #2 AWG and 1 #8 AWG ground wire) to the distribution panel (100-amp sub panel).

I would like to install a 7.6 kw inverter. (To keep things simple in this post I will ask a question about the inverter size in another post.) To control costs, I would like to avoid a meter tap. I have experience installing electrical panels and sub panels. I researched the possible solutions and found a viable one.

The solution would be to replace the subpanel with a 200-amp sub panel. Use a 100-amp 2 pole breaker to backfeed (with hold down screw). And use a 40-amp breaker for the Inverter. The thing that make me doubt about this solution is that the 200-amp subpanel will still be feed by 100-amp cable (#2 AWG). Is this solution NEC compliant? Thank you very much.

[scrambler]

If I understood right, you have a similar configuration as mine.

A single 100 amp meter breaker panel, that does not need to meet the 120% rule as it can only hold that single 100 amp breaker, so the sum of all the overcurrent devices in that panel will never exceed 100 amps (one of the Alternate rule panels must comply with). And that panel can never see more than 100 amps.

Then a Sub Panel that holds all the house loads,fed by that 100 amp breaker, and the 40 amps inverter breaker would be installed at the end of the busbar (assuming there is space).

If so, that Sub panel needs to satisfy the 120% rule as the bus bar can be overloaded with current from both the grid and the inverter. All it needs is a 125 Amp rated busbar so that the panel satisfies the 120% rule.

The wires coming from the 100amp breaker and feeding the Sub Panel do not need a 125amp rating, as there will never be more than 100 amps traveling through these wires.

[bcroe]

Then a Sub Panel that holds all the house loads,fed by that 100 amp breaker, and where the 40 amps inverter breaker will be installed at the end of the busbar.

So you are saying, all house loads must be on (moved to) the sub panel? Bruce Roe

[scrambler]

Not at all.
May be I misunderstood his configuration.
I understood his house loads are in a sub panel fed by a 100 amp breaker located in the meter panel, and the inverter breaker would go in that SubPanel.
This is exactly my configuration, he can confirm if I misunderstood what he meant.

[solarix]

If you want 40A of backfeed (7.6kW inverter), you have to either replace the main panel with 200A (and include these costs in your 30% fed tax credit), or isolate your subpanel with a breaker downstream of the solar backfeed (add another subpanel with a 100A branch breaker upstream of the existing subpanel and backfeeding into this new subpanel), or do a line side tap before the Main service disconnect breaker. (very few service panels are listed for this modification).

[JSchnee21]

A line side tap seems like the easiest solution - if there is no AHJ to inspect, there is no reason why a licensed electrician cannot do this. These are very common in NJ for example -- on larger PV installs -- and we are a very strong trade union state. A line side tap is very inexpensive if using clamp on splices. Much less so than installing and wiring a sub panel.

I guess a bigger question in my mind would be your current / longer term plans for how to wire/integrate a backup generator with your solar PV system. Assuming you'll be grid tied, and already have/or plan to get a generator, you'll need some extensive wiring to accommodate the transfer switch and isolate your home/generator from the Solar/grid when running in island mode.

[peakbagger]

One possibility is that some (not all) utilities offer a line side tap that is close to "plug and play". Its a specialized device that plugs into the meter socket and then the meter plugs into it.

Here is one brand I found searching the web http://connectder.com/products/.

[ButchDeal]

One possibility is that some (not all) utilities offer a line side tap that is close to "plug and play". Its a specialized device that plugs into the meter socket and then the meter plugs into it.

Here is one brand I found searching the web http://connectder.com/products/.

line side tape is generally done by an electrician and has little to nothing to do with the utility and is not plug and play.

Some utilities offer a pre-manufactured equipment that plugs into the meter housing but these are only in a few locations mostly in CA. Most other locations do not allow these devices and they can be more expensive than an electrician making a line side tap.

[JSchnee21]

Here's an example. This is not a picture of mine, but it looks very similar. Very quick and easy. If installed poorly, it can be a source of high feed in resistance. Similarly, if the mains conductors are damaged during the install, they could heat under heavy current load. While I would have preferred a proper junction box, this would have added at least $1000 and is not commonly done.

Most smaller installs use a load side feed in breaker in the existing panel, assuming it passes the 120% rule. For larger installs (>7.6kW), you almost get a line side tap.

Insulation Piercing Tap.jpg

[josepr]

Thank you for all the suggestions. In summary my main doubt is this: Do I satisfy the 120% rule if I'm using a 200-amp panel with a 7.6 KW inverter even thought the feeder cable and the service cable is rated for 100-amp? Is using a 200-amp panel with a 100-amp feeder cable in compliance with NEC?

The situation is that for residential accounts only one meter is allowed. So, I can't do a supply side tap. The integrated 100-amp combo meter/panel is old and I have not found an UL approved bus tap (the connection from the meter to the breaker is a bus, not a cable). The problem is that the combo meter/panel is in a concrete wall. And replacing it and/or making a tap (before or after the breaker) will be expensive.

The cheaper solution, in this case, would be to put a small 200-amp panel between the 100-amp combo meter/panel and the 100-amp distribution panel. Put a 100-amp input breaker and one 100-amp breaker to feed the distribution panel and one 40-amp breaker for the inverter. The only problem I have is that I'm not sure if this is acceptable under NEC. Does the 120% rule apply only to the panel where the inverter is connected, or do I need to replace the service and feeder cable with 200-amp cable?

[scrambler]

It definitely sounds like you have the same configuration as I have and I went through the same questions.

The sub panel that will hold the inverter breaker, if upgraded to a 200 amp bus bar and fed by a 100 amp breaker will satisfy the 120% rule.

The Meter breaker panel with the single 100 amp is the core of the issue.
If like me that panel has a single inline breaker and cannot hold any other breaker, it physically never can see anything else than 100 amps, and therefore does not need to satisfy the 120% rule.

That said, sometimes inspectors can try to apply rules in a blanket fashion, so I did the following.

1) I went to the city permit office and showed the Permit solar engineer diagram below of my installation and asked if the fact the outside main disconnect 100 Amps breaker is in a 100 amps panel would be a problem, and would they require to have it upgraded to 125 Amps. My configuration has a battery and a critical loads SubPanel, but you can just ignore that part

He Confirmed that panel was fine as it is at 100 amps with a 100 amps breaker for the reason mentioned above and did not need to be upgraded.

2) I then did the same with PG&E application engineer, and she too confirmed they had no problem with that panel being 100 amps with a 100 amps breaker.

3) Finally I checked the 2014 705.12(D)(2) code regulation text and found the following
The actual text of the code down below specifies that in order to comply, each panel only needs to meet ONE of the three possible requirements (a, b or c).

The main panel by the meter with a single 100 amps breaker satisfies requirement (c), as it has a single 100 amps breaker (and can never hold any other), therefore the sum of amp rating of all overcurrent devices in that panel is 100 amps, and it does not exceed the rating of the busbar even if assumed to be only 100 amps.
--------------------------------------------------------
ACTUAL 2014 705.12(D)(2) TEXT:
(3) Busbars. One of the methods that follows shall be used to determine the ratings of busbars in panelboards.
(a) The sum of 125 percent of the inverter(s) output circuit current and the rating of the overcurrent device protecting the busbar shall not exceed the ampacity of the busbar.
Informational Note: This general rule assumes no limitation in the number of the loads or sources applied to busbars or their locations.

(b) Where two sources, one a utility and the other an inverter, are located at opposite ends of a busbar that contains loads, the sum of 125 percent of the inverter(s) output circuit current and the rating of the overcurrent device protecting the busbar shall not exceed 120 percent of the ampacity of the busbar. The busbar shall be sized for the loads connected in accordance with Article 220. A permanent warning label shall be applied to the distribution equipment adjacent to the back-fed breaker from the inverter that displays the following or equivalent wording:
WARNING: INVERTER OUTPUT CONNECTION; DO NOT RELOCATE THIS OVERCURRENT DEVICE.
The warning sign(s) or label (s) shall comply with 110.21(B).

(c) The sum of the ampere ratings of all overcurrent devices on panelboards, both load and supply devices, excluding the rating of the overcurrent device protecting the busbar, shall not exceed the ampacity of the busbar. The rating of the overcurrent device protecting the busbar shall not exceed the rating of the busbar. Permanent warning labels shall be applied to distribution equipment that displays the following or equivalent wording:
WARNING: THIS EQUIPMENT FED BY MULTIPLE SOURCES. TOTAL RATING OF ALL OVERCURRENT DEVICES EXCLUDING MAIN SUPPLY OVERCURRENT DEVICE, SHALL NOT EXCEED AMPACITY OF BUSBAR.

Below is the Schematic
SImple Schematic.jpg
Now to be fair, We just submitted the permit, so we are yet to see if it will pass...
I can keep you posted...

[JSchnee21]

scrambler,

How do you like your PIKA system? Is it up and running? Roughly how long of a run time do you get on battery? I assume you don't have any/much shade on you array? How many kWh of battery did you get? Will the PIKA system support adding generator input in the future?

If you don't mind me asking, how much was the total system, roughly or in terms of $/W?

[scrambler]

I will let you know once it is installed (if the permit gets approved as is...)


To answer in more details

How do you like your PIKA system?
On paper I like the technology, the integration of the whole system and the modularity of the battery.
Real life feedback will have to wait a bit.

Is it up and running?
No

Roughly how long of a run time do you get on battery?
The critical loads panel will have 7 breakers to cover some lights, fridge, sum pump, Computer/TV/Internet, Furnace fan, garage door...
These amount to a max load of about 3,200W, but should not represent more than 6kWh per 24 hours period . Given the battery has an 11.4 kWh usable capacity, this means that even with no sun at all, we could go 2 days, but with sun we would not be limited.

I assume you don't have any/much shade on you array?
No I only get some passing shade in the early hours of the morning during the 6 winter month. I figured with 3 strings and the Qcell Duo G5 that are cut cell panels, the impact should not be too bad.
I have a thread on that below
https://www.solarpaneltalk.com/forum...mpact-question

How many kWh of battery did you get?
the Flex / Harbor 4 with 4 modules. Total 13.5kWh, 11.4 usable

Will the PIKA system support adding generator input in the future?
I dont know, you may want to contact them, they have been pretty responsive so far.

Price wise, I live in an area where prices are overinflated...
The configuration is probably 10/12k above a non battery system, I should get about 3k of extra rebate from for it from the SGIP program.
So after SGIP and the 30% tax credit that makes it 5 to 6k more

[JSchnee21]

Great, thanks! Best of luck. Yeah, realistic storage pricing seems to be $10-15K minimum. Perhaps more if you want to "run the whole house" -- or just simplify the wiring.

I can buy a really, really nice stationary 1800rpm NG generator (Generac Protector QS

[JSchnee21]

Darn, rest of my post got cut off. Anywho, you can get a Generac Protector QS 22kW NG generator for $9K. $12-14K fully installed and run the entire house forever. Of course that much NG gets pricey after a while as my neighbors learned during hurricane Sandy when we lost power for ~10 days.