705.12 (D) re- visited

[ggunn]

So a conductor can be both a feeder and part of the inverter output circuit. Why is that awkward or a problem?

Cheers, Wayne

I don't understand his fixation on what you call those conductors.

 

[GoldDigger]

So a conductor can be both a feeder and part of the inverter output circuit. Why is that awkward or a problem?

Cheers, Wayne

For the same reason that some people cannot accept that a conductor can be both a feeder and a branch circuit conductor. Some insist that the definitions should be "fixed" or else any such conductor is somehow illegal.

 

[david]

So a conductor can be both a feeder and part of the inverter output circuit. Why is that awkward or a problem?

Cheers, Wayne

A feeder is defined in the NEC. The PV solar source is load side connected to the normal systems distribution equipment. Yes the PV source current makes it's way to the utility source using the normal systems distribution equipment.

I don't understand his fixation on what you call those conductors.

Because when a solar system installer does not apply the PV source calculations to the conductors and bussbars in series with the PV source connection point it is being suggested that i can write a corrective order.

Violation 705.2 see definition of inverter output circuit. Please make the following correction the source calculations must be applied to all busbarrs and conductors in series with the inverter output.

 

[david]

For the same reason that some people cannot accept that a conductor can be both a feeder and a branch circuit conductor. Some insist that the definitions should be "fixed" or else any such conductor is somehow illegal.

I am not suggesting that the PV source calculations not be applied to the equipment bussbars and the feeders in series with the utility source to the inverter output circuits for a load side connection point. I am trying to determine when not done that way, how to write it up as a violation of the NEC.

 

[david]

Mr. Brooks did respond to my email I sent.
In part he responded.

“David,

Thank you for your thoughtful email. I’m not clear on the problem that the (somewhat poor) definitions of inverter output circuit has for enforcing the NEC.

In the 2017 NEC, we got rid of all the detail in the Article 690 definition and it simply states:

Inverter Input Circuit. Conductors connected to the dc input of an inverter.

Inverter Output Circuit. Conductors connected to the ac output of an inverter.”


“The inverter output circuit conductors terminate at the circuit breaker they are connected to.”

 

[jaggedben]

I suspect he did not understand your question. If you ask him "for an interactive system, load-side connected to a utility service through two panelboards connected in series, what rules apply to the upstream panelboard", he would say 705.12.

I didn't know they changed the definition in 690 but I'm pretty sure it did not change in 705.

 

[wwhitney]

A feeder is defined in the NEC. The PV solar source is load side connected to the normal systems distribution equipment. Yes the PV source current makes it's way to the utility source using the normal systems distribution equipment.

That all sounds good. Where's the problem?

Because when a solar system installer does not apply the PV source calculations to the conductors and bussbars in series with the PV source connection point it is being suggested that i can write a corrective order.

Violation 705.2 see definition of inverter output circuit. Please make the following correction the source calculations must be applied to all busbarrs and conductors in series with the inverter output.

Sounds good to me.

Cheers, Wayne

 

[david]

That all sounds good. Where's the problem?


Sounds good to me.

Cheers, Wayne

Well it might be good if the inverter output circuits did not terminate at the breaker they are connected to.

The somewhat poor definition of inverter output circuits is a descriptive definition taken from article 690 in its application was descriptive of a service equipment and line side connection point, In its description does not address a load side connection point. Applying that definition to a load side connection point and defining the feeder distribution conductors and bussbars connected in series with the connection point as inverter output circuits is awkward at best and not a correct application of the definition given in article 705.2

 

[david]

I suspect he did not understand your question. If you ask him "for an interactive system, load-side connected to a utility service through two panelboards connected in series, what rules apply to the upstream panelboard", he would say 705.12.

I didn't know they changed the definition in 690 but I'm pretty sure it did not change in 705.

ok,
Please tell me how to write a violation referencing a code section that states not applying the PV source calculations to the bussbars and conductors in series with the connection point is a violation of the NEC.

Again we all are stating it is correct to do it that way. I could bluff the homeowner and point to the definition of inverter output circuits. But knowing that the definition is incorrect to apply that way, I am not comfortable trying to bluff to achieve a correct installation.

 

[wwhitney]

Applying that definition to a load side connection point and defining the feeder distribution conductors and bussbars connected in series with the connection point as inverter output circuits is awkward at best and not a correct application of the definition given in article 705.2

We're going to have to disagree. It is neither awkward nor incorrect.

We've dissected the definition completely, and for a site where the only power sources are PV and the utility, the definition reduces to "Conductors between the inverter and the service equipment". Pretty simple, actually.

Cheers, Wayne

 

[wwhitney]

Here you go:

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 unbolded wording doesn't apply when there is no other "electric power production source". So ignore it.

Cheers, Wayne

 

[jaggedben]

^ What Wayne said.

It's not a bluff. You're the AHJ, and it's your interpretation, if you want it to be.

 

[ggunn]

ok,
Please tell me how to write a violation referencing a code section that states not applying the PV source calculations to the bussbars and conductors in series with the connection point is a violation of the NEC.

Again we all are stating it is correct to do it that way. I could bluff the homeowner and point to the definition of inverter output circuits. But knowing that the definition is incorrect to apply that way, I am not comfortable trying to bluff to achieve a correct installation.

Once again, 705.12(D)(2)(3)(b) has it covered. It says, "When two sources, one a utility and the other an inverter, are located at opposite ends of a busbar...". Pick any panel in a series of panels between a service and an inverter. The utility feed is located at one end of the busbar and the inverter feed is located at the other. It makes no difference if the feed (either feed or both) is direct or through another panel; the 120% rule applies. The rating of the breaker feeding the bus from the utility side is used because it limits the virtually infinite available fault current from the utility, and 125% of the inverter output current is used for that side of the equation because the inverter is a current limited device.

Not only is it what this interpretation of the code says, it makes sense. Not only that, but every AHJ I have dealt with also interprets it this way. It's well plowed ground.