That subsection states, in part, "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 underlined part is the MCB. Load device are load breakers. Supply devices is subjective. I believe there's somewhere that states you can use 125% of inverter output rating(s) for upstream determinations... anyone?
PV plan check
- Thread starter cowboyjwc
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ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
The way it's written you use 125% of the inverter nameplate rating for 705.12(D)(2)(3)(b) but the solar breaker rating for 705.12(D)(2)(3)(c). Of course, you can use different sections for different panels in series.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
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- Electrician
Sorry, I misunderstood. I thought thought there was only one panel, the service panel with 400 bus with a 200 amp main breaker
But I still dispute that that is "exactly" what you said. You left out the "ampacity of the busbar" part
sorry to nitpick, but that made it seem you were interpreting the rule differently.
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- Location
- Simi Valley, CA
Oh you can nitpick all you want, I'm married with children. No what I have is a 200 amp panel with a 200 amp bus bar feeding a 400 amp panel.Sorry, I misunderstood. I thought thought there was only one panel, the service panel with 400 bus with a 200 amp main breaker
But I still dispute that that is "exactly" what you said. You left out the "ampacity of the busbar" part
Or to reexplain it in solar terms, solar array to inverters, inverters to 90 amp solar breaker in a 400 amp panel with a 200 feeder, to a 200 amp main service panel/load center with a 200 amp bus.
Sierrasparky
Senior Member
- Location
- USA
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- Electrician ,contractor
Cowboy,
Maybe I am missing something. Why don't these folks just add a new meter for the solar?
Maybe I am missing something. Why don't these folks just add a new meter for the solar?
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
POCO may not be willing to add another meter, especially if the state has Net Metering laws.
Sierrasparky
Senior Member
- Location
- USA
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- Electrician ,contractor
Cowboy is in Southern CA.
To the best of my recollection the POCO there will allow a separate meter.
jaggedben
Senior Member
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- Northern California
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- Solar and Energy Storage Installer
Even if the utility allows it without extra fees and charges, which I doubt, adding another meter is a huge extra expense compared to a load side connection.
Also Cowboy mentioned batteries and if the intention is to island with solar power to when the grid goes down, that ain't gonna work if the power and loads are on separate meters.
Also Cowboy mentioned batteries and if the intention is to island with solar power to when the grid goes down, that ain't gonna work if the power and loads are on separate meters.
mwm1752
Senior Member
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- Aspen, Colo
(2) Bus or Conductor Ampere Rating. One hundred twentyfive percent of the power source output
circuit current shall be used in ampacity calculations for the following:
(1) Feeders. Where the power source output connection is made to a feeder at a location other than the opposite end of the feeder from the primary source overcurrent device, that portion of the feeder on the load side of the power source output connection shall be protected by one of the
following:
a. The feeder ampacity shall be not less than the sum of the primary source overcurrent device and 125 percent of the power source output circuit current.
200A primary source overcurrent device in 200a panel feeding 400 a panel with 200 amp feeder(250 ser al??? 3/0 cu thhwn? ????) 400 amp panel has 90a PV source(125% of output circuit) Yes?????
would that make the feeder required to be rated @ 290 amps??? Just thinking outside the box in this unusual circumstance.
That's from the 2011 edition. He's under the 2014 NEC I believe and the changes have some significant requirement impact.
jaggedben
Senior Member
- Location
- Northern California
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- Solar and Energy Storage Installer
No it would not make the feeder required to be rated 290A, and I highlighted the reasons why not in the language you quoted. There is no portion of the feeder that is on the load side of the power source output connection.
Actually he was quoting the 2014 or 2017 NEC.
My bad. Sorry, mwm1752.
mwm1752
Senior Member
- Location
- Aspen, Colo
jaggedben
Senior Member
- Location
- Northern California
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- Solar and Energy Storage Installer
The question is whether the source current comes from the opposite end of the feeder as the utility or not. If it is at the opposite end then the currents can't add together (Kirchoff's law). If they can come from the same direction and go to a load then they are not at the opposite ends.
A connection in a panelboard is at the opposite end of the feeder from the utility feed.
A feeder tap to an inverter is not at the opposite end.
If an inverter output is in a panelboard with subfeed lugs that have no OCPD, that is not at the opposite end; both utility and inverter can feed the feeder in the same direction.
That is somewhat irrelevant. The power goes where the load is. Either the load needs to be completely protected, or the arrangement needs to be such that sources can't add together.
mwm1752
Senior Member
- Location
- Aspen, Colo
"There is no portion of the feeder that is on the load side of the power source output connection." Your quote not mine, which brought up the question "Doesn't PV send power (load) back to the grid if not used by the structure it serves??" so there is relevance -- You did notice I agreed with theory ---- using code language a feeder is not the conductors from utility to service equipment so they are not referencing the utility feed.
No comment on the calculations?
No comment on the calculations?
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
I am struggling a bit to get what you are saying. Current flowing from the PV back to the grid subtracts from (not adds to) the current flowing from the grid.
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
Not sure what we are actually talking about here now, but to try to clear up some things...
I was using 'utility' where the proper code term is 'primary source'. The latter term does not imply any distinction between what side of the service point you are on. Power can come from either the primary source or the interconnected source, or both. But, Kirchoff's law says that current can only flow from one at a time between two nodes. The important thing is that, if a load (or set of loads on a feeder) can draw from both sources through the same node, then overcurrent protection must be arranged so that it protects the load. If the sources are at opposite ends of the feeder then no additional overcurrent protection is required. If they are not, then there needs to be an additional overcurrent device between the load and the source interconnection overcurrent device. (Branch circuits are okay because by definition they have protection at the node where they connect, and sources are not allowed to mix with loads in branch circuits.)
I was using 'utility' where the proper code term is 'primary source'. The latter term does not imply any distinction between what side of the service point you are on. Power can come from either the primary source or the interconnected source, or both. But, Kirchoff's law says that current can only flow from one at a time between two nodes. The important thing is that, if a load (or set of loads on a feeder) can draw from both sources through the same node, then overcurrent protection must be arranged so that it protects the load. If the sources are at opposite ends of the feeder then no additional overcurrent protection is required. If they are not, then there needs to be an additional overcurrent device between the load and the source interconnection overcurrent device. (Branch circuits are okay because by definition they have protection at the node where they connect, and sources are not allowed to mix with loads in branch circuits.)
mwm1752
Senior Member
- Location
- Aspen, Colo
Had to look at your profile & understand better -- I do not , have not,will not dispute theory you keep repeating I was asking for code interpretation -- Am I correct to decipher you are not a licensed Electrician but may hold a NABCEP license ----- Have you installed AC wiring legally? You are commenting on NEC installations for AC --
The calculations are derived from a simple service, size of feeder to a panel, -- the capacity of buss in panel terminated in & maximum size of breaker for an interconnected power source as well as feeder conductor size is determined through section 705.12.
Terminology is imperative to discussion & the fusing at the transformer(primary source overcurrent device) & the service lateral (feeder) as you seem to understand it as does not fit into the topic as presented for we would be discussing a supply side connection IMO. We will get no where with a difference of definition.
The calculations are derived from a simple service, size of feeder to a panel, -- the capacity of buss in panel terminated in & maximum size of breaker for an interconnected power source as well as feeder conductor size is determined through section 705.12.
Terminology is imperative to discussion & the fusing at the transformer(primary source overcurrent device) & the service lateral (feeder) as you seem to understand it as does not fit into the topic as presented for we would be discussing a supply side connection IMO. We will get no where with a difference of definition.
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
A service lateral is not a feeder, and we're not talking about anything on the utilty's side of the service point. (Yes, terminology is important.)
Here is a very long video but as I recall Mike and his group do a good job of discussing these issues. Check out the 26:20 mark for an illustration of a PV connection 'other than at the opposite end' of a feeder. I figured some diagrams might help. The video has lots of them.
As far as the qualification question, I'm legally qualified in the state of California to do any of the work we've been discussing in this thread. And I've done plenty of it.
Here is a very long video but as I recall Mike and his group do a good job of discussing these issues. Check out the 26:20 mark for an illustration of a PV connection 'other than at the opposite end' of a feeder. I figured some diagrams might help. The video has lots of them.
As far as the qualification question, I'm legally qualified in the state of California to do any of the work we've been discussing in this thread. And I've done plenty of it.
Correction....
Current flowing from the PV back to the grid means there is no current flowing from the grid to the local system(s). Current cannot flow in both directions at the same time.
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