Thread: 690.64(B) 2005 Edition NEC

A common point of connection for a PV system is thru a dedicated CB to the panel's busbar. When feeding a dwelling's panel busbar, the sum of the supply breakers can be up to 120% of the rating of the busbar.
In my way of thinking, if I have a 125 amp busbar protected by a main breaker of 100 amps, this provision would allow a 50 amp PV breaker. 125 amps X 1.2 = 150 amps....150 amps minus 100 amps = 50 amps. Correct?

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Fred,

This is that 2005 NEC section. (bold and underlining are mine)
- 690.64 Point of Connection.
- - The output of a photovoltaic power source shall be connected as specified in 690.64(A) or 690.64(B).
- - (A) Supply Side. A photovoltaic power source shall be permitted to be connected to the supply side of the service disconnecting means as permitted in 230.82(6).
- - (B) Load Side. A photovoltaic power source shall be permitted to be connected to the load side of the service disconnecting means of the other source(s) at any distribution equipment on the premises, provided that all of the following conditions are met:
- - - (1) Each source interconnection shall be made at a dedicated circuit breaker or fusible disconnecting means.
- - - (2) The sum of the ampere ratings of overcurrent devices in circuits supplying power to a busbar or conductor shall not exceed the rating of the busbar or conductor.
- - - - Exception: For a dwelling unit, the sum of the ampere ratings of the overcurrent devices shall not exceed 120 percent of the rating of the busbar or conductor.
- - - (3) The interconnection point shall be on the line side of all ground-fault protection equipment.
- - - - Exception: Connection shall be permitted to be made to the load side of ground-fault protection, provided that there is ground-fault protection for equipment from all ground-fault current sources.
- - - (4) Equipment containing overcurrent devices in circuits supplying power to a busbar or conductor shall be marked to indicate the presence of all sources.
- - - - Exception: Equipment with power supplied from a single point of connection.
- - - (5) Circuit breakers, if backfed, shall be identified for such operation. Dedicated circuit breakers backfed from listed utility-interactive inverters complying with 690.60 shall not be required to be individually clamped to the panelboard bus bars. A front panel shall clamp all circuit breakers to the panelboard bus bars. Main circuit breakers connected directly to energized feeders shall also be individually clamped.

This is my take on that:
- (1) Each source interconnection shall be made at a dedicated circuit breaker or fusible disconnecting means.
- - Jerry's take: Sound simpler than it is worded, what is your take on what I am saying - "Each source", that includes the utility power source feeders as well as the PV feeders, which means that there now 'must be' a 'main' breaker or fuse at the connection of BOTH to the distribution panel busbar. Which means that if this is not the service equipment, a 'panel main' - for lack of a better term - is required to be added for the utility power feeder connection to the busbar. What say you?

- (2) The sum of the ampere ratings of overcurrent devices in circuits supplying power to a busbar or conductor shall not exceed the rating of the busbar or conductor.
- - Exception: For a dwelling unit, the sum of the ampere ratings of the overcurrent devices shall not exceed 120 percent of the rating of the busbar or conductor.
- - - Jerry's take on Exception combined with what was stated in (1): Let's presume that a distribution panel with 150 amp rated busbar is fed from a 150 amp main, with 150 amp rated feeders, which now are required to be connected to the bus through a 150 amp breaker serving as a 'panel main' for utility power, with the PV system being connected through a second breaker serving as a 'panel main' for PV power. The distribution panel bus is only rated at 150 amps, with already one 150 amp breaker supplying it, which means that the breaker for the PV 'panel main' will not be allowed to be greater than 20 percent of 150 amps, or 30 amps. The solution, then, would be to use a 225 amp rated panel, leaving ampacity for a 120 amp PV panel main. This is the question you are asking, but (1) above plays a big role in this as I am reading it.

Is that how you were thinking and asking about it?

I just used different numbers, but the math problem was the same.

I did used those different numbers because it is not infrequent when the main and the panel rating match instead of having excess rating for the panel bus over the main rating as in your example. Just making it 'trickier' and possibly 'more real world' like for installations.

100 amp x 125% = 125 amps.

125 amp x 80% = 100 amps.

Panel rating.

100% rating for OCPD or 80% rating.

Most mains are not 100%.

Design to the lowest common element - usually the OCPD rating.

1.2 or 120% is not the inverse of 80%.

80% of 150 amps is 120 amps. 125% of 120 amps is 150 amps.

FYI/FYH:

http://nolazed.com/download/fs/11%20gridconnect.ppt

I have determined that I am correct in my calculations. Thanks for your responses.

Yes Fred You are correct

Originally Posted by H.G. Watson, Sr.

100 amp x 125% = 125 amps.

125 amp x 80% = 100 amps.

Panel rating.

100% rating for OCPD or 80% rating.

Most mains are not 100%.

Design to the lowest common element - usually the OCPD rating.

1.2 or 120% is not the inverse of 80%.

80% of 150 amps is 120 amps. 125% of 120 amps is 150 amps.

H.G., I was referring to the Photo-Voltaic supply to the CB mounted at the lower end of the busbars in a main service panel. A panel having 125 amp-rated busses is permitted to be exceed by 120% for residential PV supply. When you subtract that from the rating of the OCPD from utility source that is protecting the bus, the remainder is the amount of the maximum breaker size for the point of connection (CB) of the PV system.

The 80% info you were discussing has to do with OCPD for bus protection from the utility side. It is not a part of the required calculations for my example.

Protecting the bus and conductors from fault at 150 amps or greater:

With 100% rated main at 100 amps, and 125 amp rated bus, 50 amps@ 100%.

With 80% rated 100 amp CB only 25 amps.

100 amps (80% rated) x 125% = bus fault @ 125 amps.

Bus rating 125 amps x 120% residential exception = 150 amps. 150 amps - 125 amps bus fault from POCO = remaining 25 amps for PV fault via bus.

{Fault current from DC = 156% (125% x 125%). (reverse 64%).}

Interactive still delivering until main opens to clear fault, is what I'm thinking (or missing?!?) worst case scenario.

H.G.: The current is coming to the bus from the PV array to a 50 ampere (not to exceed) CB connected to the 125 amp bus bars of the panelboard. This panelboard is fused at 100 amps for loads that are being drawn with the array off (not contributing). The sources are paralell. The OCPD of the non-PV loads is not in question. I already know the answer. The bus can share two sources. Faults on the PV side are protected by the 50 amp POC CB. Faults from the normal loads are protected by the 100 amp OCPD.

Originally Posted by H.G. Watson, Sr.

Most mains are not 100%.

Many, if not most, of the mains I have seen were at the panel busbar rating.

Which is why I gave my example.

That condition DOES exist, and it exists A LOT.

Just to forward a contact for a Photovoltaic expert.
John Wiles-
jwiles@nmsu.edu

He gives out this email at his seminars, and says that he will reply.
This is the guy who NFPA talks to about PV. He is extremly active with PV and helped write article 690 in the NEC

...Sigh...Forest, trees. bus and conductors. Giving up its more frustrating describing a color to one born blind.

OCPD can't clear fault (open) without adequate bond. Its not just hots and grounded conductors you're protecting.

Think occurance in panel.

Bus rating 125 amps. 125 amps x 1.2 = 150 amps.

50 amps interactive PV.

Reduce main breaker to 80 amps for 50 amps PV.

Main 80 amps 80% rated, 80 x 125% = max current if fault prior to Main opening = 100 amps

50 amps via PV still delivering no fault until Main opens at +100 amps.

Current on bus = 150 amps before trip. Surge can trip/Fault can clear safely. No heat damage to bus.



100 amp Main 80% max current prior to open main 125 amps.
50 amps via interactive PV still delivering current up to main trip, no fault on inverter side, so until main opens means 175 amps on bus prior to main trip - exceeded tolerance on bus from exception by 25 amps, surge, fault no clear, main not trip before heat damage bus.

175 amps is 1.4 times 125 amps, not 1.2 times.

Here's a link to J. Wiles article: http://www.re.sandia.gov/en/ti/tu/Co...%20NEC2000.pdf

references 1999 NEC.

Might find this cross reference list to 1999 sections to 2002 sections helpful:

http://www.houwire.com/pdf/nec_2002_1999.pdf

Originally Posted by H.G. Watson, Sr.

...Sigh...Forest, trees. bus and conductors. Giving up its more frustrating describing a color to one born blind.

I am so sorry to hear you were born blind ...

If I had know I would have taken that into consideration ...

Okay, through considering it ... you apparently have no redeeming value, at least not which you are displaying here.

Originally Posted by Jerry Peck

I am so sorry to hear you were born blind ...

If I had know I would have taken that into consideration ...

Okay, through considering it ... you apparently have no redeeming value, at least not which you are displaying here.

Talk about a dictionary-perfect example of a messiah complex!

You aren't my redeemer, you aren't the Messiah, and you won't be the judge.

Watson, old chap,

Do I really bug you that much simply by pointing out YOUR FLAWS, inconsistencies, untruths, lies and post changing, and your inability to admit you can be, and are, WRONG at times?

It certainly appears to be so.

In which case I must be hitting right on target with those truths.

One of your problems you will see, if you go back and read your own posts, you will find that you mostly follow this MO:

You must degrade someone about something.

Without providing any back up documentation.

You must show that you think you know more.

Without providing any back up documentation.

And, when you think you are providing documentation help, you point us to "the NEC", "the NFPA 54", "the blah, blah, blah" without actually providing anything of usefulness.

Then, to try to defend your lack of doing so you try to state something to the effect of 'well, it is copyrighted and I am not allowed to' when in fact it may be copyrighted and you are allowed to. There are times I have wondered how long you had to debate with yourself to even say "NEC" or "NFPA 54" as those are also copyrighted terms. Oh, jeez, look out, there is the copyright police looking over your shoulder fiddling with their handcuffs because you did not say "NEC copyrighted by NFPA" ...

Your posts first (usually first before anything else) must degrade someone, only after doing that will you post something you think may be useful, and it rarely is useful, might as well say 'It is in the library - go find it and look it up.'

Fred Warner,

You are limited to backfeeding PV to the difference.

This is how you apply the 1.2 rule.

Main panel rating lets say is 200 amps.

Panel rating x 1.2 - panel rating = max amp rating 2005 NEC allows for backfed PV.


200amps x 1.2 - 200 equals 40 amps.

125 amps x 1.2 - 125 amps = 25 amps.

I found the 2005 NEC updated version of John Wiles "White Paper". (Its on a different server and access).

You can go here to download it free:

PVnecSugPract

Chose option one (smaller file).

See especially pages beginning at 118 (E-24) of 149 and the next few

And

Appendix M at pages 143 and 144 of 149 of the PDF document.

OR you can use the search feature (the binoculars icon) and type "690.64" (without the quotes) in the search box. The last seven or so links will take you to the pages I mentioned.

Originally Posted by H.G. Watson, Sr.

Protecting the bus and conductors from fault at 150 amps or greater:

With 100% rated main at 100 amps, and 125 amp rated bus, 50 amps@ 100%.

With 80% rated 100 amp CB only 25 amps.

100 amps (80% rated) x 125% = bus fault @ 125 amps.

Bus rating 125 amps x 120% residential exception = 150 amps. 150 amps - 125 amps bus fault from POCO = remaining 25 amps for PV fault via bus.

{Fault current from DC = 156% (125% x 125%). (reverse 64%).}

Originally Posted by H.G. Watson, Sr.

Interactive still delivering until main opens to clear fault, is what I'm thinking (or missing?!?) worst case scenario.

Originally Posted by Fred Warner

H.G.: The current is coming to the bus from the PV array to a 50 ampere (not to exceed) CB connected to the 125 amp bus bars of the panelboard. This panelboard is fused at 100 amps for loads that are being drawn with the array off (not contributing). The sources are paralell. The OCPD of the non-PV loads is not in question. I already know the answer. The bus can share two sources. Faults on the PV side are protected by the 50 amp POC CB. Faults from the normal loads are protected by the 100 amp OCPD.

Originally Posted by H.G. Watson, Sr.

Fred Warner,

You are limited to backfeeding PV to the difference.

This is how you apply the 1.2 rule.

Main panel rating lets say is 200 amps.

Panel rating x 1.2 - panel rating = max amp rating 2005 NEC allows for backfed PV.


200amps x 1.2 - 200 equals 40 amps.

125 amps x 1.2 - 125 amps = 25 amps.

I found the 2005 NEC updated version of John Wiles "White Paper". (Its on a different server and access).

You can go here to download it free:

PVnecSugPract

Chose option one (smaller file).

See especially pages beginning at 118 (E-24) of 149 and the next few

And

Appendix M at pages 143 and 144 of 149 of the PDF document.

Did my best trying to remember the WHY covered in a seminar long ago.
Definately check the why with the author and code developer.

Either way, the 1.2 rule is applied in the article/white paper by the GURU of PV.

Since he helped to write the code - I'd think he's the one who knows how it is applied.

H.G.: If I had two strings these parallel currents would add together. The 125% increase over the PV output circuit current is to account for the standard listing of conductors to 80% of maximum circuit current for continuous duty. See 690.8(B)(1). The minimum photovoltaic output circuit conductor ampacity is the sum of the maximum current of the parallel source circuits. In this sense, the 80% comes into play. But this is off topic for my OP.

H.G.Watson-
according to the "guru of PV" John Wiles Fred's original post is correct.
I have been to John's seminars and have his latest seminar manual.
He even shows what Fred is saying in an example.
Contact John Wiles 575-646-6105, jwiles@nmsu.edu, or fax 575-646-3841.

Originally Posted by ken horak

H.G.Watson-
according to the "guru of PV" John Wiles Fred's original post is correct.
I have been to John's seminars and have his latest seminar manual.
He even shows what Fred is saying in an example.
Contact John Wiles 575-646-6105, jwiles@nmsu.edu, or fax 575-646-3841.

Thanks for your help, Ken.

Originally Posted by Fred Warner

H.G.: If I had two strings these parallel currents would add together. The 125% increase over the PV output circuit current is to account for the standard listing of conductors to 80% of maximum circuit current for continuous duty. See 690.8(B)(1). The minimum photovoltaic output circuit conductor ampacity is the sum of the maximum current of the parallel source circuits. In this sense, the 80% comes into play. But this is off topic for my OP.

Originally Posted by ken horak

H.G.Watson-
according to the "guru of PV" John Wiles Fred's original post is correct.
I have been to John's seminars and have his latest seminar manual.
He even shows what Fred is saying in an example.
Contact John Wiles 575-646-6105, jwiles@nmsu.edu, or fax 575-646-3841.

I am in agreement with Ken, Fred is correct.

Thanks, Jerry.