I'm in the planning process of a solar install at my house. I'm planning on installing a PV system of about 17-18 kW. I'm trying to figure out the most economical way to satisfy the NEC 120% rule at the main panel. I was planning on replacing the main panel anyway because I've been doubling up breakers and am out of slots. My current panel has a 200 amp breaker and a 200 amp rated busbar. I thought a good solution would be to find a main breaker panel with a 200 amp main breaker and a busbar rated for over 250 amps. I tried looking for electrical panels with 250 or 300 amp busbars but haven't found any yet. It seems that most panels cap out at around 225 amps. I'm not sure if the best option is to look for a 400 amp panel and install a 200 amp breaker in it. I'm trying to get ahold of Eaton tech support but haven't heard back yet. I was wondering if someone else has run into this and has already found a solution. I briefly looked at installing 400 amp service but that was extreme overkill and quite expensive. Thanks.
Electrical Panel Upgrade for NEC 120% Rule
- Thread starter brad14
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
One way, if possible is to change the existing 200 amp breaker to a 150 amp main which would then allow 90 amps for the solar assuming a 200 amp bus.
That would be possible but I was planning on replacing the panel anyway and I don't want to reduce capacity. Thanks for the suggestion though.
You just need space but not amps? Go with what Dennis said. Chnge to a panel with more space, but change the 200 amp breaker to a 150, that will allow your PV amps.
Most residences will never use 200 amps, regardless of how many breakers are in the panel.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Dennis' suggestion is the simplest, and 99.99% likely to be absolutely fine. You could go with a 225/200 which, considering a typical dc-ac ratio, would likely work with a 18 KW system. Beyond that, you would probably have to move up into a true panel board where you can get anything you want. for example Siemens smallest panelboard, a P1 all have a 250 amp buss. going with a true panelboard is super nice of course, but it's probably going to be twice as much as a load center style. Finally, you could of course do a supply-side connection, or bring in another set of service entrance conductors via 230.40 exception 2 and tie the solar into that. oh one more thing, if this happens to be a ground Mount I would use to 230.40 exception 3 and run service conductors out to the array.
hillbilly1
Senior Member
- Location
- North Georgia mountains
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- Owner/electrical contractor
Square D iLine, boss has a 600 amp one on his house.
ramsy
NoFixNoPay Electric
- Location
- LA basin, CA
- Occupation
- Service Electrician 2020 NEC
2017 NEC has the 120% rule at 705.12(B)(2)(b) thru (d)
18kw of solar / 240v = 75 x 125% = 94, works on center-fed 200A panels if no other breakers exist on the same bus section, in violation of 705.12(B)(2)(c)
18kw of solar / 240v = 75 x 125% = 94, works on center-fed 200A panels if no other breakers exist on the same bus section, in violation of 705.12(B)(2)(c)
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ramsy
NoFixNoPay Electric
- Location
- LA basin, CA
- Occupation
- Service Electrician 2020 NEC
The license board recommends 3-competitive bids, so consumers might avoiding the panel flipper trying to force this kind of unnecessary construction.
Not quite sure I follow. What’s the licensing board got to do with changing a panel?
Here you get a permit for every change you can change a panel as many times as you want until the AHJ gets tired of fooling with you..
ramsy
NoFixNoPay Electric
- Location
- LA basin, CA
- Occupation
- Service Electrician 2020 NEC
See post #5.
If electrofelon was among the bidders, his supply side connection avoids the unnecessary construction of panel flippers
If electrofelon was among the bidders, his supply side connection avoids the unnecessary construction of panel flippers
Carultch
Senior Member
- Location
- Massachusetts
You do have a burden of proof when you reduce the size of an existing main breaker. Either to show a load calculation, or a month of 15-minute interval load data, to demonstrate that the loads are unlikely to nuisance trip the 150A main breaker.
Most likely, the 200A was just selected as a nice round number/standard equipment size when the panelboard was originally built, and it is extremely conservative for what a typical residence will realistically consume.
Carultch
Senior Member
- Location
- Massachusetts
Bear in mind that just because you might be using a 400A panelboard to meet the 120% rule, doesn't necessarily mean that it is a 400A service. The service is based on the trip rating of the main service disconnect, rather than the busbar rating of the main panel. So if it has a 200A main on a 400A panel, it is still considered a 200A service. The upstream equipment associated with the service, such as the meter socket, service conductors, and connections to the utility, are still based on a 200A service.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
Best check with the POCO, I believe mine has a rule (for residential at least) that the service size has to match the service equipment size. [Not sure of the rationale, perhaps the concern is that if the service equipment has a larger rating, you could easily put in a larger service OCPD without telling them.] Of course, you could still do 200A meter - 200A disconnect - 200A feeder - 400A panelboard.
Cheers, Wayne
I’m curious here, not doubting at all...
service size has to be the same..
200 amp overhead service from POCO going to be 4/0 alum, or #2?
I’m feeding a 200 amp service with #2 (conch) rated at 150 amps @90
UG would be 2/0 for about 150’. 4/0 for longer distances to keep VD at a minimum.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Sometimes poco's come up with a stupidest things.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
I think I found the requirement in PG&E's Greenbook, section 1.14 "Determining the Service Rating"
1.14(A). PG&E Service Rating: The rating of the PG&E service to be supplied is the current rating in amperes of the electrical enclosure where PG&E
terminates and connects its supply facilities and conductors.
So if you put up a 400A meter/main with a 200A main breaker, PG&E is going to treat that as a 400A service, and require that you comply with the all 400A service requirements.
Cheers, Wayne
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
That seems poorly worded and ambiguous to me for many situations. I am not familiar will that utility territory and the methods, but I would think many times there is NOT "an
electrical enclosure where PG&E
terminates and connects its supply facilities and conductors." I.e. an overhead service with the service point at the drip loop, or where the service point is at a transformer vault or hand hole. Besides that, I would say an "enclosure" does not typically have a current rating.
curt swartz
Electrical Contractor - San Jose, CA
- Location
- San Jose, CA
- Occupation
- Electrical Contractor
The PG&E requirements primarily concern underground services. If you install a 400 amp service termination they require that you install underground substructures (raceways, vaults, transformer pads) that will support a 400 amp service. They will then decide what size wire and transformer to install to feed the current load. If at a later time they feel need to increase the size/number of conductors or transformer they can easily do it.
rainwater01
Member
- Location
- Greenwood Indiana
- Occupation
- Electrician
So could you just get a 320 amp meter base and parallel lug out to a 200 amp disconnect for the house and a 100 amp disconnect for solar? Here in Indiana we just call for a meeting with a poco engineer when we upgrade our services to see if there good with our plans and need to change anything on their end.
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electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Yes I usually prefer to do it that way. Bring in another set of SEC using 230.40 ex #2 to a new panel and qualify the busbar under the "sum off all OCPD's except the one protecting the busbar" rule. A class 320 base is not required, a box or wireway could be used, but I find the class 320 is clean and convenient.
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