705.12 (D) re- visited

[ggunn]

First off your building a normal distribution to a sub panel at the load end of a feeder and going strictly by what the code says . The first thing to ask is how many slots does the 100 amp sub panel have.
Is it capable of supplying branch circuits and feeders. The installer says it s just to combine the PV inverters outputs. Ok what side of the PV meter is it on. The inspector needs to make a decision.

Now the main service panel I know what previous codes said. So I say you need to do a source calculation on the main MDP. The installer says on both points where does it say that in the code.

The number of slots in the 100A sub is irrelevant; it is compliant because the total ratings of all breakers, supply and load, excluding the OCPD protecting the busbar, does not exceed rating of the panel per 705.12(D)(2)(3)(c).

A PV meter is not required by the NEC. If the AHJ requires one they will decide where it needs to go. That's irrelevant to what I proposed; it would be between the subpanel and the inverter.

The MDP is in violation on two points. The breaker protecting the busbars in the sub must be at the opposite end of the busbar from the main breaker, and the 100A from the inverter must fit within 120% of the busbar rating minus the main breaker rating. There is only 40A headroom in a 200A panel with a 200A breaker.

I have done hundreds of PV projects from a few kW to over a MW under this interpretation of the NEC in at least 10 jurisdictions. Agreement from inspectors on these points has been 100%.

 

[ggunn]

The number of slots in the 100A sub is irrelevant; it is compliant because the total ratings of all breakers, supply and load, excluding the OCPD protecting the busbar, does not exceed rating of the panel per 705.12(D)(2)(3)(c).

A PV meter is not required by the NEC. If the AHJ requires one they will decide where it needs to go. That's irrelevant to what I proposed; it would be between the subpanel and the inverter.

The MDP is in violation on two points. The breaker protecting the busbars in the sub must be at the opposite end of the busbar from the main breaker, and the 100A from the inverter must fit within 120% of the busbar rating minus the main breaker rating. There is only 40A headroom in a 200A panel with a 200A breaker.

I have done hundreds of PV projects from a few kW to over a MW under this interpretation of the NEC in at least 10 jurisdictions. Agreement from inspectors on these points has been 100%.

Correction: my 1.2MW project was under the 2011 NEC, but I have one at 812kW now being built under 2014 where these rules played a major role.

 

[david]

The number of slots in the 100A sub is irrelevant; it is compliant because the total ratings of all breakers, supply and load, excluding the OCPD protecting the busbar, does not exceed rating of the panel per 705.12(D)(2)(3)(c).

First, I was at the office and did not have access to the 2014 code until I got here at home.

I should not have answered until I looked at the specific section above. As an authority the number of slots is relevant to me in evaluating a distribution panel in determining if 705.12 (D)conditions are met to even apply 705.12 (D)

That being said I agree that under 705.12(D)(2)(3)(c)the sub panel would be compliant.

A PV meter is not required by the NEC. If the AHJ requires one they will decide where it needs to go. That's irrelevant to what I proposed; it would be between the subpanel and the inverter.

I never said a PV meter was required and I only mentioned it as a tool in trying to resolve if 705.12(D) is applicable to the sub-panel if a discussion about the panel capable of supplying other loads needed resolution.

The MDP is in violation on two points. The breaker protecting the busbars in the sub must be at the opposite end of the busbar from the main breaker, and the 100A from the inverter must fit within 120% of the busbar rating minus the main breaker rating. There is only 40A headroom in a 200A panel with a 200A breaker.

In following the NEC manual style, I pointed out the controlling statement, that limits this section to the point of PV source connection as covered in the conditions laid out in 705.12(D)

I further do not see any requirement in 705.12(D) (1) or 705.12 (D) (2). I can say 1 know it should be that way all I want but without a rule that says “shall be used in the calculations for all busbars and conductors.” As stated before the authorities you mentioned have no way to get there.

I have done hundreds of PV projects from a few kW to over a MW under this interpretation of the NEC in at least 10 jurisdictions. Agreement from inspectors on these points has been 100%.

How many of these inspectors where already familiar with earlier versions of the NEC?

 

[david]

I agree with you guys on the points you are making i just do not agree that as written the 2014 NEC can get you there with a shall be requirement

 

[jaggedben]

The NEC defines an inverter output circuit (in multiple places) as the conductors between the inverter and the service equipment (that definition needs work, but it says that much). So if there are multiple connections in series, they are all inverter output connections and each subject to the appropriate rules in 705.12. If an installer is trying to tell you that an upstream connection is not an inverter output connection then point him/her back to the definition of inverter output circuit to show them that it is.

(Load conductors that are not in series are by definition not between the inverter and service, and thus are not part of the inverter output circuit.)

I don't have the 2014 book in front of me to make specific arguments about the language, but I think that what I say above is broadly implied and you cannot consistently read the code another way.

 

[david]

The NEC defines an inverter output circuit (in multiple places) as the conductors between the inverter and the service equipment (that definition needs work, but it says that much). So if there are multiple connections in series, they are all inverter output connections and each subject to the appropriate rules in 705.12. If an installer is trying to tell you that an upstream connection is not an inverter output connection then point him/her back to the definition of inverter output circuit to show them that it is.

(Load conductors that are not in series are by definition not between the inverter and service, and thus are not part of the inverter output circuit.)

I don't have the 2014 book in front of me to make specific arguments about the language, but I think that what I say above is broadly implied and you cannot consistently read the code another way.

So are you saying 705.12 (D) (2) (1) feeders conductors supply side(not addressed in the code section) of the PV source connection point in series with the service equipment are subjected to a size increase 125% of the inverter output?

690.2
Inverter Output Circuit. Conductors between the inverter and an ac panelboard for stand-alone systems or the conductors between the inverter and the service equipment or another electric power production source, such as a utility, for electrical production and distribution network.

705.2
Utility-Interactive Inverter Output Circuit. The conductors between the utility interactive inverter and the service equipment or another electric power production source, such as a utility, for electrical production and distribution network.

The inverter output circuit regardless of it being a utility interactive inverter or not are the conductors that connect to service equipment. Or they are the conductors that connect to another power production source.

The definition as applied to article 705 simply says the inverter output connects to the service equipment [main overcurrent device(s)]. The service equipment has utility service conductors connected to the equipment already because it is a interconnected system, 705.12 is saying you are permitted to move the connection ahead (supply side) or you are permitted to move the connection after (load side)of the service equipment, [main overcurrent device(s)].

 

[david]

This whole discussion has gotten way to involved and we are never going to agree because we do not agree with what this sentence means.

In systems with panelboards connected in series, the rating of the first overcurrent device directly connected to the output of a utility-interactive inverter(s) shall be used in the calculations for all busbars and conductors.

You guys have taken the position that the sole purpose of the sentence was to direct you to a correct value when doing a calculation.

And I disagree that the meaning of that sentence has that sole purpose. I have the position that the sentence has an additional purpose of directing that the calculation shall be applied to all busbars and conductors in series with the inverter output to the service equipment.

Your position is the calculation is already implied and by removing the sentence did not effect the content of the rule that it shall be applied to all busbars and conductors in series.

The sentence is not needed any longer because there no longer can be any confusion over what what breakers rating is applicable for the calculation since it is no longer based on any breakers rating rather the sum of 125% of the inverters output.

We are not going to agree that the sentance can have only one meaning (or purpose) so we just need to disagree

 

[Carultch]

This whole discussion has gotten way to involved and we are never going to agree because we do not agree with what this sentence means.

In systems with panelboards connected in series, the rating of the first overcurrent device directly connected to the output of a utility-interactive inverter(s) shall be used in the calculations for all busbars and conductors.

You guys have taken the position that the sole purpose of the sentence was to direct you to a correct value when doing a calculation.

And I disagree that the meaning of that sentence has that sole purpose. I have the position that the sentence has an additional purpose of directing that the calculation shall be applied to all busbars and conductors in series with the inverter output to the service equipment.

Your position is the calculation is already implied and by removing the sentence did not effect the content of the rule that it shall be applied to all busbars and conductors in series.

The sentence is not needed any longer because there no longer can be any confusion over what what breakers rating is applicable for the calculation since it is no longer based on any breakers rating rather the sum of 125% of the inverters output.

We are not going to agree that the sentance can have only one meaning (or purpose) so we just need to disagree

The way that I understand that sentence is as follows:

Suppose you interconnect 20A of PV at a 100A subpanel with a 100A main. Then this subpanel is fed from a 200A main panel, that has a 200A main. The 100A breaker to feed the subpanel is at the opposite end from the main supply

That sentence is telling you that only the 20A breaker for PV at the first subpanel matters for all the calculations. You don't need to think about the fact that you are interconnecting at the main panel with a 100A breaker, you only need to use the 20A in the calculation of 20+200 < 1.2*200.


And in NEC2014, they've now revised the language so it isn't the breaker rating that matters in the 120% rule, but rather the current and safety factor that drives its size. So for a 3 kW inverter, the current is 12.5A, which 1.25*this = 15.625A, which means a 20A breaker. You don't use 20A in the 120% rule, you instead now get to use 15.625A in the calculation, if 2014 applies to you.

 

[david]

The way that I understand that sentence is as follows:

Suppose you interconnect 20A of PV at a 100A subpanel with a 100A main. Then this subpanel is fed from a 200A main panel, that has a 200A main. The 100A breaker to feed the subpanel is at the opposite end from the main supply

That sentence is telling you that only the 20A breaker for PV at the first subpanel matters for all the calculations. You don't need to think about the fact that you are interconnecting at the main panel with a 100A breaker, you only need to use the 20A in the calculation of 20+200 < 1.2*200.


And in NEC2014, they've now revised the language so it isn't the breaker rating that matters in the 120% rule, but rather the current and safety factor that drives its size. So for a 3 kW inverter, the current is 12.5A, which 1.25*this = 15.625A, which means a 20A breaker. You don't use 20A in the 120% rule, you instead now get to use 15.625A in the calculation, if 2014 applies to you.

And in your example with you understanding of the rule since shall by the NEC manual style is a mandatory rule you cannot use 25 amps or greater in doing the calculation in your example.

In my reading of the rule you have a mandatory rule that the calculation shall be done on the bussbars and conductors in series from the inverter output to the service equipment.

And understanding the NEC style you could always use 25 amps or 100 amps for the calculation if you chose to but the value the calculation is based on is the 20 amp breaker rating not the 100 amp breaker rating.

Since when did the NEC ever have a rule that you could not exceed its min. safety standards?

You have to decide if it is a mandatory rule dictating that the calculation be done or is it a mandatory rule directing you to an absolute value that you must use.
I agree that the sentence had the effect of clarifying the value that could be enforced on the installer to use. In your example not the 100 amp breaker rather the 20 amp breaker.

I ‘m just not there with you that the code did not allow the calculation by choice to be based on any in excess of 20 amps

 

[jaggedben]

So are you saying 705.12 (D) (2) (1) feeders conductors supply side(not addressed in the code section) of the PV source connection point in series with the service equipment are subjected to a size increase 125% of the inverter output?

Absolutely. That's part of the inverter output circuit according to the definitions you quoted, and subject to 705.60(B). Forget 705.12 for minute; the inverter output conductor sizing is required by other parts of the code. (The load side of the feeder in 705.12(D)(2)(1) is not part of the inverter output circuit, which is why a special rule is required for it (because of the potential for currents to add together).

705.12 is the point of connection but it is not the only code section that governs inverter outputs.

 

[david]

Absolutely. That's part of the inverter output circuit according to the definitions you quoted, and subject to 705.60(B). Forget 705.12 for minute; the inverter output conductor sizing is required by other parts of the code. (The load side of the feeder in 705.12(D)(2)(1) is not part of the inverter output circuit, which is why a special rule is required for it (because of the potential for currents to add together).

705.12 is the point of connection but it is not the only code section that governs inverter outputs.

Than i need to revisit Mike Holt's video on this and think about it.

Iin his video he uses the example of a feeder breaker feeding a 200 amp feeder to a 200 amp sub- panel with a 200 amp main.

The feeder is tapped with 200 amps of PV source. He indicated that the feeder portion load side of the pv source connection point needed to be increased to 400 amp feeder as one option,

and the secound option was to provide 200 amp over current protection at the point
the 200 amp feeder and the 200 amp PV source connetion point came together load side of the PV source connection point

I believe he addressed the 200 amp feeder section that became supply side of the 200 amp PV source connection point by saying no increase in size was required for the supply side of the connection point.

The supply side of the connection point would be in series from the 200 amp PV source inverter output to the service equipment.
The only size correction that was done was to the portion that both currents would be load side of both sources.

And yes the 200 amp feeder portion supply side of the 200 amp inverter connection point was bottled between 200 amp breakers.

The 125% correction as i understand it is for continuous loading not over current protection

 

[Carultch]

And in your example with you understanding of the rule since shall by the NEC manual style is a mandatory rule you cannot use 25 amps or greater in doing the calculation in your example.

In my reading of the rule you have a mandatory rule that the calculation shall be done on the bussbars and conductors in series from the inverter output to the service equipment.

And understanding the NEC style you could always use 25 amps or 100 amps for the calculation if you chose to but the value the calculation is based on is the 20 amp breaker rating not the 100 amp breaker rating.

Since when did the NEC ever have a rule that you could not exceed its min. safety standards?

You have to decide if it is a mandatory rule dictating that the calculation be done or is it a mandatory rule directing you to an absolute value that you must use.
I agree that the sentence had the effect of clarifying the value that could be enforced on the installer to use. In your example not the 100 amp breaker rather the 20 amp breaker.

I ‘m just not there with you that the code did not allow the calculation by choice to be based on any in excess of 20 amps

You are putting words in my mouth, if you think that I am saying that you CANNOT use a higher ampere value to represent the PV in these examples. That is not what I am saying.

I'm saying what I understand the rule to be that specifies what the NEC minimum is. The NEC does not say that you cannot make a situation that is more conservative than the calculations prescribe. The NEC is the minimum standard of safety.

 

[david]

You are putting words in my mouth, if you think that I am saying that you CANNOT use a higher ampere value to represent the PV in these examples. That is not what I am saying.

I'm saying what I understand the rule to be that specifies what the NEC minimum is. The NEC does not say that you cannot make a situation that is more conservative than the calculations prescribe. The NEC is the minimum standard of safety.

I’m not putting words into your mouth I’m saying the section has a mandatory rule if you say that the mandatory rule is directed at the value of the 20 amp breaker than the value is 20 amps.

If you want to interpret the rule to say you are required to use 20 amps as a min value in determining code compliance. Ok, than what are you directed to do with that value.

Your position seems to be you are given no direction in that section only the min. mandatory value used to do the calculation.

You arrive at that conclusion because you personally already know what to do with that value

As far as enforcement of that section there is the statement about applying the calculation to all conductors and busses in series.

 

[david]

Than i need to revisit Mike Holt's video on this and think about it.

Iin his video he uses the example of a feeder breaker feeding a 200 amp feeder to a 200 amp sub- panel with a 200 amp main.

The feeder is tapped with 200 amps of PV source. He indicated that the feeder portion load side of the pv source connection point needed to be increased to 400 amp feeder as one option,

and the secound option was to provide 200 amp over current protection at the point
the 200 amp feeder and the 200 amp PV source connetion point came together load side of the PV source connection point

I believe he addressed the 200 amp feeder section that became supply side of the 200 amp PV source connection point by saying no increase in size was required for the supply side of the connection point.

The supply side of the connection point would be in series from the 200 amp PV source inverter output to the service equipment.
The only size correction that was done was to the portion that both currents would be load side of both sources.

And yes the 200 amp feeder portion supply side of the 200 amp inverter connection point was bottled between 200 amp breakers.

The 125% correction as i understand it is for continuous loading not over current protection

It may be that it was assumed the PV source was 160 amps since the source breaker was 200 amps

or maybe option 1 should have been a 360 amp feeder

 

[david]

Absolutely. That's part of the inverter output circuit according to the definitions you quoted, and subject to 705.60(B). Forget 705.12 for minute; the inverter output conductor sizing is required by other parts of the code. (The load side of the feeder in 705.12(D)(2)(1) is not part of the inverter output circuit, which is why a special rule is required for it (because of the potential for currents to add together).

705.12 is the point of connection but it is not the only code section that governs inverter outputs.

690.2
Inverter Output Circuit. Conductors between the inverter and an ac panelboard for stand-alone systems or the conductors between the inverter and the service equipment or another electric power production source, such as a utility, for electrical production and distribution network.

705.2
Utility-Interactive Inverter Output Circuit. The conductors between the utility interactive inverter and the service equipment or another electric power production source, such as a utility, for electrical production and distribution network.

To be consistent we have to define what the service equipment is, since that portion of the definition is the same exact language in article 690.2 and article 705.2

The disconnects that disconnect the PV source output conductors from all other non PV conductors and equipment

I would define the inverter output circuits as the conductors prior to load distribution. I would apply 705. 60(B) accordingly.

 

[ggunn]

I further do not see any requirement in 705.12(D) (1) or 705.12 (D) (2). I can say 1 know it should be that way all I want but without a rule that says “shall be used in the calculations for all busbars and conductors.” As stated before the authorities you mentioned have no way to get there.

I've already posted the interpretation I believe says that. An inverter feeds a panel whether it is through a dedicated breaker or through a feeder to a subpanel and the 120% rule applies using 125% of the inverter's rated output current. My inspectors agree.

How many of these inspectors where already familiar with earlier versions of the NEC?

All of them, as far as I know. Most of them, for sure. Functionally nothing has changed from the 2011NEC except that you use 125% of the inverter output current instead of the breaker rating. Using the breaker rating made you unnecessarily round up the inverter current a second time. IMO you are getting too hung up in the linguistics of the code and not thinking about the physics of what is really going on.

 

[jaggedben]

Than i need to revisit Mike Holt's video on this and think about it.

Iin his video he uses the example of a feeder breaker feeding a 200 amp feeder to a 200 amp sub- panel with a 200 amp main.

[etc.]...

It would be helpful if you clarified which video (i.e. post a link), but I believe I have seen it and there is no contradiction between it and anything I've said in this thread.

To be consistent we have to define what the service equipment is, since that portion of the definition is the same exact language in article 690.2 and article 705.2

The disconnects that disconnect the PV source output conductors from all other non PV conductors and equipment

If you're saying that the service equipement is the PV disconnect that is tremendously wrong. Service equipment is defined in article 100.

I would define the inverter output circuits as the conductors prior to load distribution. I would apply 705. 60(B) accordingly.

That is tremendously wrong. Feeders and load distribution and interactive inverter output conductors are not mutually exlusive. The same equipment or conductors can be both. Only branch circuits are not allowed to be shared between load and inverter output functions.

Inverter output circuits are defined in the code, as already discussed. You don't get to use your own definition.

 

[david]

I’m not making up my own definitions I’m interpreting the definition given.

You seem to be interpreting the term service equipment in the definitions given to be the utility service equipment

I am interpreting the term service equipment in the definition given to be the PV source service equipment

By my application of the definition the inverter output circuits would be a point prior to load distribution

690.2
Inverter Output Circuit. Conductors between the inverter and an ac panelboard for stand-alone systems or the conductors between the inverter and the service equipment or another electric power production source, such as a utility, for electrical production and distribution network.
• Conductors between the inverter and an ac panelboard for stand-alone systems
o Panelboard = load distribution equipment
 the conductors between the inverter and the service equipment
o service equipment = the point the inverter circuit conductors are disconnected from loads
 the conductors between the inverter and another electric power production source, such as a utility, for electrical production and distribution network.

In my view the inverter output circuit is on the supply end of any load.

230.2 Number of Services.
A building or other structure served shall be supplied by only one service unless permitted in 230.2(A) through (D). For the purpose of 230.40, Exception No. 2 only, underground sets of conductors, 1/0 AWG and larger, running to the same location and connected together at their supply end but not connected together at their load end shall be considered to be supplying one service.

(5) Parallel power production systems


705.1 Scope.
This article covers installation of one or more electric power production sources operating in parallel with a primary source(s) of electricity.

Service Equipment. The necessary equipment, usually consisting of a circuit breaker(s) or switch(es) and fuse(s) and their accessories, connected to the load end of service conductors to a building or other structure, or an otherwise designated area, and intended to constitute the main control and cutoff of the supply.

Disconnecting Means. A device, or group of devices, or other means by which the conductors of a circuit can be disconnected from their source of supply.

705.2
Utility-Interactive Inverter Output Circuit. The conductors between the utility interactive inverter and the service equipment or another electric power production source, such as a utility, for electrical production and distribution network.

 

[ggunn]

I’m not making up my own definitions I’m interpreting the definition given...

Discretion being the better part of valor, I am going to bow out of this discussion. I have designed a whole lot of solar and I have a very good record of systems passing inspections on the first pass, and I would really like to help anyone who needs it, but all this haranguing over fine points and sentence syntax in the code has worn me out. This thread has devolved, IMO, into arguing for the sake of arguing, so I'll leave it to you.

Peace,
Gordon

 

[david]

Discretion being the better part of valor, I am going to bow out of this discussion. I have designed a whole lot of solar and I have a very good record of systems passing inspections on the first pass, and I would really like to help anyone who needs it, but all this haranguing over fine points and sentence syntax in the code has worn me out. This thread has devolved, IMO, into arguing for the sake of arguing, so I'll leave it to you.

Peace,
Gordon

Actually I appreciate your point of view and your time given to this discussion.

And since you where kind with your valued time on the subject.

I will tell you it is not for the sake conflict. We are the Authority but we are a third party under contract to enforce and administer this code with several municipalities. When you install receptacles we have Authorities that require grounds up because that is there preference. We are a business and in dealing with the competition we have stated to municipalities we strive to enforce what the code says, not our option of what we believe the code should say.

Those boundaries get blurred when I have to say the safety is implied in the text as written