Panel requirements for grid tie in for 10k watt system

[dschmidt@unitizing]

Hello, I am investigating a solaredge 10k watt grid tie in system for my home. I currently have a 2 - 200 amp service supply from the utility company, one for my house and one for my garage. I am being informed that I can only use a 40 amp backfeed breaker in my 200 amp breaker panel. And to maximum the 10k watt system I need a 60amp backfeed breaker. So I either need to upgrade my service to a larger capacity service or break the system in 2 and feed in into my house panel and the second one into the other separate service that feeds my garage.

I would really like to get rid of the service to my garage and feed it from the panel in my house. I have been searching and cannot find a solution on how to tie in the 10k watt solar into my service panel.

I did read something about a fuse disconnect and distribution panel located next to the meter box as a possible option. but at this point I am confused on how this should tie into my existing 200 amp service.

Thanks in advance for any assistance to helping me understand how this all ties together.

Thanks, Dave

[sensij]

The general rule is that you can add PV supply up to 20% more than the panel is rated. A 200 A panel (with a 200 A main breaker) * 1.2 = 240 A, which is where the 40 A limit you've run into comes from. One alternative is to drop the size of the main breaker on that panel... lowering to a 175 A breaker on your 200 A panel would give you another 25 A of solar that you could add, or 65 A total. (175 + 65 = 240 A).

I did read something about a fuse disconnect and distribution panel located next to the meter box as a possible option. but at this point I am confused on how this should tie into my existing 200 amp service.

This is probably referring to a "line side" or "supply side" installation, which is done between the meter and the main electrical panel. If your local authority allows it, and you find an installer with experience, it can be another code compliant alternative.

[HX_Guy]

As mentioned, you can derate your main house breaker from 200A to 175A and then you can accommodate a 60A breaker. This is what was done at my house, it's a very simple procedure but it does have to be done with the utility company is on site so they can remove their meter to stop the power while the main breaker is being swapped out.

[inetdog]

Hello, I am investigating a solaredge 10k watt grid tie in system for my home. I currently have a 2 - 200 amp service supply from the utility company, one for my house and one for my garage. I am being informed that I can only use a 40 amp backfeed breaker in my 200 amp breaker panel. And to maximum the 10k watt system I need a 60amp backfeed breaker. So I either need to upgrade my service to a larger capacity service or break the system in 2 and feed in into my house panel and the second one into the other separate service that feeds my garage.

I would really like to get rid of the service to my garage and feed it from the panel in my house. I have been searching and cannot find a solution on how to tie in the 10k watt solar into my service panel.

I did read something about a fuse disconnect and distribution panel located next to the meter box as a possible option. but at this point I am confused on how this should tie into my existing 200 amp service.

Thanks in advance for any assistance to helping me understand how this all ties together.

Thanks, Dave

The number 40 comes from the application of the 120% rule to the panel bus bars.
The rule states that the sum of the input from the main breaker and the backfeed from solar breaker(s) cannot be more than 120% of the bus rating of the panel. So 200 + PV must not exceed 200 x 1.2; 240 - 200 = 40.
However there are several important details this analysis leaves out:

1. The bus bar rating in many 200A panels is actually 225A, not 200A. This will give you a 120% figure of 270A instead of 240A. Try to find out what the actual bus bar rating of your panel is. You may have to go to the manufacturer to get this information, or it may be somewhere on the panel labeling or catalog information.
2. Your 10K system would have an output rating of 41.7A at 120V. The NEC requires that you multiply this by 1.25 since it is a continuous (more than three hour) current. So the wire and breaker size must be at least 52.2A. I believe the next larger standard breaker size is 60A, so you would go with that.
The 2014 NEC requires you to do the backfeed calculation using the 52.2A figure rather than the 60A breaker size, but that still would not help you if your panel has a 200A bus.
3. And here is the really good part: Since your garage is very unlikely to need the full 200A breaker, you can just reduce the size of the main breaker in that panel to get you into conformity. If you use a 180A main breaker, then you would have your 60A of backfeed allowance.

Finally, if your POCO allows it, you can instead do what is called a supply side connection and put your 60A backfeed breaker in a separate third box or panel which connects directly to the meter, just as the other two panels do. In that case you are only limited by the size of your utility service. If you have a 400A service, you could backfeed a full 400A if you wanted a gargantuan system and if your POCO would allow that big a system under their residential PV rules.

So, you can still play with various ideas including moving the garage to the first panel (often not a great idea, since you may run out of breaker space), but you probably do not have to do anything that drastic just to connect your PV legally.

[inetdog]

As mentioned, you can derate your main house breaker from 200A to 175A and then you can accommodate a 60A breaker. This is what was done at my house, it's a very simple procedure but it doesn't have to be done with the utility company is on site so they can remove their meter to stop the power while the main breaker is being swapped out.

I think you mean "does".

[HX_Guy]

I think you mean "does".

Oops...yes, DOES.

[inetdog]

Oops...yes, DOES.

A regular licensed electrician is very unlikely to be willing to do the swap "HOT" although a solar installer may try pushing his luck. Hope his insurance coverage is good.

[dschmidt@unitizing]

Thanks for the responses, I understand the issue. So with my understanding, could I resolve the issue with the following solution?

Install a new 300 or 400 amp rated distribution panel between my meter box and my 200 amp breaker panel. In this new panel, I would feed from meter box with a 200 amp breaker as the input breaker, feed my house breaker panel with a 200 amp breaker, feed my garage with a 100 amp breaker, then install the 60 amp feedback breaker for my solar inverter feed.

This would resolve the 125% of the 200amp bus, allow me to feed my house, garage and solar system with distrubing most of my existing setup.

I have 2 other questions:

1. To feed my garage with 100 amps. @ approx 100 feet, what size wire would I need.

2. My solar array will be approx 50 feet from my existing house meter box, would you recommend placing the inverter near the meter box and run the high voltage dc the 50 feet, or mount the inverter on the garage near the solar array and run the 220vac cables to the meter box the 50 feet?

Thanks, Dave

[control4userguy]

Honestly, you might want to re-consider derating existing breaker(s). Unless you are Gas Monkey Garage or something, you won't be creeping-up on 200A draw ever.

[inetdog]

Just one comment about an off the wall strange utility policy:
In Los Angeles the DWP requires that the nominal panel size (not the installed main breaker size) match the service rating or be smaller. One member on another Forum tried putting in a 400A panel on an existing 200A service, with a 200A main breaker of course, mainly to avoid the 120% rule problems.
Well DWP insisted that he either go back to a 200A panel or pay for an upgrade to 400A service.
Have not heard of any such idiocy anywhere else so far.

[dschmidt@unitizing]

I understand the cost may be eye opening. I was looking if the concept would actually work. I also understand that I need to contact my electric company to verify their requirements for larger amperage panel.

Also any input on my 2 other questions would be helpful

Thanks, dave

[Carl_NH]

Thanks for the responses,

1. To feed my garage with 100 amps. @ approx 100 feet, what size wire would I need.

2. My solar array will be approx 50 feet from my existing house meter box, would you recommend placing the inverter near the meter box and run the high voltage dc the 50 feet, or mount the inverter on the garage near the solar array and run the 220vac cables to the meter box the 50 feet?

Thanks, Dave

Dave,

Assume the PV system is ground mounted and not on house or garage and you want to capture the total usage of house and garage?

I was faced with a similar situation last year, house service 150A, garage service 100A, separate meters and bills and with a 7.2KW array on the garage.

Locally PSNH our POCO allows for group net metering so we get credit $.18 KWH for over production so they send a check each month for excess created. We pay $.16 per KWH for the house so it didn't make sense for me to run the wiring from house panel to the garage.

In my situation to tie the house and garage was an update to the house panel to 200A, a sub panel for the garage and a 4 wire with ground underground to the garage - estimate of $6K.

So it depends on your location and local rules, and in my case host Net metering made the most sense short term. It depends on your local POCO policy.

Carl

[PVAndy]

Most locations do no allow Group ( Virtual Nete Metering)

A line side tap is much easier and cheaper than a larger panel or downsizing the main breaker.

We probably do 3 or 4 of them a week. All it takes is a 60A fused disconnect with 60A fuses tied into the main panel above the main circuit breaker. You need to keep the fused disconnect within 10 feet of the main panel and use #6 wire. Tie onto the main wires with Ilsco lugs (commonly called Bugs)

What ever disconnect you use in a line (or supply side tap) the wire must be sized to the rating of the disconnect not the fuses in it.

Also this disconnect is now considered "Service Equipment" and must be rated and installed as such ie Grounding Bushings

BTW Anytime we have a Generator transfer switch we do a line side tap, usually in the transfer switch on the line side. If the utility won't allow line side taps (I've never run into this in over 3000 systems) then ask them if they allow whole house automatic transfer switches which is essentially the same thing.

Andy

PV Design Engineer

[dschmidt@unitizing]

Thank you for your response. I looked up ILSCO products and found part‘# GTA-350-350 @ a cost of $35 each.

To make sure I completely understand, to use 6awg wire I need to install a disconnect rated at 65 amps. I cannot install a disconnect rated at 100amps with a 60 amp breaker/fuse. Is this correct?

Most locations do no allow Group ( Virtual Nete Metering)

A line side tap is much easier and cheaper than a larger panel or downsizing the main breaker.

We probably do 3 or 4 of them a week. All it takes is a 60A fused disconnect with 60A fuses tied into the main panel above the main circuit breaker. You need to keep the fused disconnect within 10 feet of the main panel and use #6 wire. Tie onto the main wires with Ilsco lugs (commonly called Bugs)

What ever disconnect you use in a line (or supply side tap) the wire must be sized to the rating of the disconnect not the fuses in it.

Also this disconnect is now considered "Service Equipment" and must be rated and installed as such ie Grounding Bushings

BTW Anytime we have a Generator transfer switch we do a line side tap, usually in the transfer switch on the line side. If the utility won't allow line side taps (I've never run into this in over 3000 systems) then ask them if they allow whole house automatic transfer switches which is essentially the same thing.

Andy

PV Design Engineer

[PVAndy]

Thank you for your response. I looked up ILSCO products and found part‘# GTA-350-350 @ a cost of $35 each.

To make sure I completely understand, to use 6awg wire I need to install a disconnect rated at 65 amps. I cannot install a disconnect rated at 100amps with a 60 amp breaker/fuse. Is this correct?

The correct Ilsco is IPC 4/0-#6 which is about $8 to $12 Much smaller than the one you selected.

With a 10k inverter you want to use a 60A Disconnect with 60A fuses. Even though the wire may be rated at 65A you don't need use a disconnect of similar rating. It goes the other way, for service rated equipment the wire must be at least arry the maximum fuse size of the disocnnect.

Small disconnects are rated 30,60,100 & 200A Each size uses a different physical fuse size fuse. While you can use smaller fuses in a disconnect, they usually require an adapter.

Andy