Associated AC Equipment for PV?

[junkenpo621]

Hi All,

I'm trying to get confirmation on a code interpretation here. Let me give some background. My team and I have been "debating" for weeks regarding landing the combined AC GEC/EGC as permitted in 690.47(C)(3) in a subpanel bus bar, then running a new conductor back to the MSP to either land in the grounding bar or to be irreversibly crimped to the existing GEC. The interpretation comes in from 250.64(C) where sections of bus bars are allowed to be used to form a continuous GEC. It also states that the GEC is permitted to land in the "Associated AC Equipment." Half of the team thinks it is permissible to run this GEC to the subpanel grounding bar (or AC disconnect or PV meter) then run a new conductor from the enclosure to the existing GEC. The other half believes that the GEC must be unbroken and not terminated all the way to either landing in the MSP grounding bar or to where it is irreversibly crimped to the GEC and the only way you can use a second conductor is with a crimp.

We've been struggling over this for a while now and have had the input of some notable people in the PV industry, but their interpretations are (of course) divided on the matter. I was hoping that some healthy, open dialogue would help in the matter and I thank you all in advance for your input!

 

[ggunn]

Hi All,

I'm trying to get confirmation on a code interpretation here. Let me give some background. My team and I have been "debating" for weeks regarding landing the combined AC GEC/EGC as permitted in 690.47(C)(3) in a subpanel bus bar, then running a new conductor back to the MSP to either land in the grounding bar or to be irreversibly crimped to the existing GEC. The interpretation comes in from 250.64(C) where sections of bus bars are allowed to be used to form a continuous GEC. It also states that the GEC is permitted to land in the "Associated AC Equipment." Half of the team thinks it is permissible to run this GEC to the subpanel grounding bar (or AC disconnect or PV meter) then run a new conductor from the enclosure to the existing GEC. The other half believes that the GEC must be unbroken and not terminated all the way to either landing in the MSP grounding bar or to where it is irreversibly crimped to the GEC and the only way you can use a second conductor is with a crimp.

We've been struggling over this for a while now and have had the input of some notable people in the PV industry, but their interpretations are (of course) divided on the matter. I was hoping that some healthy, open dialogue would help in the matter and I thank you all in advance for your input!

In cases like this the only interpretation that counts is that of the inspector for the AHJ. I would suggest making an appointment with him (or her) and getting their take on it.

 

[jaggedben]

Note that in California we don't go on our version of the 2011 code until next year. (2013 California Electric Code). I was told by one inspector in SF that we had to do the irreversible splice until then, but next year we could start landing in the busbar.

As far as what the code says, I agree with ggunn. I think it is entirely vague and any of those interpretations could be argued for. The only authoritative help might be to look up the original substantiation for a clue as to why they put in that language.

As far as what makes some amount of logical sense to me, I think that the "Associated Equipment" is wherever the existing AC GEC lands. Basically my logic is that you can't have a solar GEC terminate in a sub and then just have an EGC between the sub and the premises GES. You're supposed to connect the solar GEC to the premises GES, so it makes sense that you follow the rules for installing the GEC all the way to location where that is done.

I do not believe that 260.64(C) was meant to apply to busbars that are used to terminate conductors. I believe it intends to refer to sections bolted to each other, as is often found in larger switchgear.

 

[dereckbc]

There has been quite a bit of discussion and confusion with the changes. But you are correct, you can use ACEG as a GEC. Have you read John Wiles PV Grounding? John is the person who wrote 690. Read these documents should help you out.

PV System Grounding by John Wiles
PV Grounding Continued by John Wiles
Are We Grounded Yet by John Wiles.

 

[Zee]

As far as what makes some amount of logical sense to me, I think that the "Associated Equipment" is wherever the existing AC GEC lands.

Interesting interpretations.
Technically, you should be able to land the DC GEC in the subpanel and done. No additional EGC or GEC conductors, crimped or otherwise, needed to connect from there back up to MSP.

I understand the "Associated AC Equipment" to mean associated with the inverter tie-in. This is wherever the PV brkr. lands.
I find this surprising myself - yet i have tied into many subpanels with no GEC back to MSP.


I know, i know, the AC GEC system doesn't extend to a sub-panel from the MSP, yet I'll take an allowance that makes installation easier whenever they are there.

I figure, the s.p. usually will have a big EGC already, minimum #8 ......
HAving installed inverters for years with no DC GEC requirements i find the whole irreversible-crimp-DC-GEC-unbroken-back-to-MSP a bit excessive. Am i wrong?

 

[jaggedben]

Interesting interpretations.
Technically, you should be able to land the DC GEC in the subpanel and done. No additional EGC or GEC conductors, crimped or otherwise, needed to connect from there back up to MSP.

I understand the "Associated AC Equipment" to mean associated with the inverter tie-in. This is wherever the PV brkr. lands.
I find this surprising myself - yet i have tied into many subpanels with no GEC back to MSP.

I take "Associated AC Equipment" to mean 'associated with the grounding electrode system' because this is in section 690.47 which is titled 'Grounding Electrode System'. There is no mention of inverter tie ins anywhere in this section.

When I have more time, maybe I will look up the 2011 ROP and we can look at the substantiation for any clue about this.

I figure, the s.p. usually will have a big EGC already, minimum #8 ......

I've seen lots of subs with only the conduit as EGC. Which perfectly fine for an EGC, but not an GEC. Beyond this, there is the issue of whether a wire EGC is installed according to 250.64(E), as called for in 690.47(C). (And which, in a nutshell, means bonding bushings.)

I know, i know, the AC GEC system doesn't extend to a sub-panel from the MSP, yet I'll take an allowance that makes installation easier whenever they are there. ...

HAving installed inverters for years with no DC GEC requirements i find the whole irreversible-crimp-DC-GEC-unbroken-back-to-MSP a bit excessive. Am i wrong?

In practical terms, it may be excessive. The whole DG GEC thing may be excessive, particularly for microinverters. But if you are arguing that the 2011 NEC doesn't require it, then yes, I think you're wrong. At any rate, none of the jurisdictions I've worked in around here would make the allowance you'd like to take, and I see no good code sections to be used in an argument with them. It will be interesting to see if they buy Enphase's argument that their new M250 doesn't require a GEC. At least I will be able to point to the manual to support my point.

BTW, are you saying that you use inverters that don't have instructions requiring a GEC? And if so, which ones?

 

[rlenz2711]

gec solar

gec solar

A inspectors view
A solar inverter is a separate derived system.
Requires a gec from the inverter to the existing gec system
can you use the existing pipe or eg to accomplish this (NO)
In a solar inverter the bonding/gec is accomplished in the inveter

Same difference if you install any separate derived ( transformer etc ) system
Only difference is you have a choice to bond in either the trans or the first disconnect, at that point you connect to build steel ect to establish your gec.

 

[jaggedben]

A inspectors view
A solar inverter is a separate derived system.
.

How about a transformerless inverter that has direct connections between the circuit conductors of both systems?

Most solar professionals seem to agree that inverters are not separately derived systems.

 

[GoldDigger]

How about a transformerless inverter that has direct connections between the circuit conductors of both systems?

Most solar professionals seem to agree that inverters are not separately derived systems.

They are, however, sources/supplies rather than loads, and yet they do not supply anything when disconnected from the grid. Which many inspectors have problems with too.

 

[mwm1752]

Hi All,

I'm trying to get confirmation on a code interpretation here. Let me give some background. My team and I have been "debating" for weeks regarding landing the combined AC GEC/EGC as permitted in 690.47(C)(3) in a subpanel bus bar, then running a new conductor back to the MSP to either land in the grounding bar or to be irreversibly crimped to the existing GEC. The interpretation comes in from 250.64(C) where sections of bus bars are allowed to be used to form a continuous GEC. It also states that the GEC is permitted to land in the "Associated AC Equipment." Half of the team thinks it is permissible to run this GEC to the subpanel grounding bar (or AC disconnect or PV meter) then run a new conductor from the enclosure to the existing GEC. The other half believes that the GEC must be unbroken and not terminated all the way to either landing in the MSP grounding bar or to where it is irreversibly crimped to the GEC and the only way you can use a second conductor is with a crimp.

All applies in 690.47(C)
690.47(C)(3) permits a single wire to be used as multiple grounding functions.
690.47(C)(6) seems to point out the common point of both systems for the EGC shall be at the AC ground point. (MDP grounding buss)
so as long as the AC MDP has at least one continuous EGC to the buss. The path of the DC EGC should be able to go to the Sub Panel to MDP using buss connections as long as it is sized properly. IMHO
690.47(A),(B),(C) appear to be 3 different circumstances

 

[Zee]

I take "Associated AC Equipment" to mean 'associated with the grounding electrode system' because this is in section 690.47 which is titled 'Grounding Electrode System'. There is no mention of inverter tie ins anywhere in this section

BTW, are you saying that you use inverters that don't have instructions requiring a GEC? And if so, which ones?

Interesting, thx.
1. I respect your opinion, after all it requires much more work, and that is integrity.
I will stick with mine. I install in some very solar intensive jurisdictions and have had no problem with s.p. tie-ins.....yet! hmy: I have to agree with you, i don't see how this meets the INTENT of the rest of the code, unless it was meant as an allowance for us solar installers. They may be wrong, and i certainly may be.

True, there is no mention of inverter tie-in in this CODE section. But much of the terminology leads me that way.
We also have agreed that this is far from clearly worded, no?

(I would never tie into a sub-p. that is not already bonded with an EGC conductor, and just a pipe as you have experienced.)

2. oh no, i mis-spoke. I run GEC's on all jobs and take great pains to follow NEC. WAY back in the day....2001 and on, when employed by others, we solar installers either didn't know, or weren't required to run DC GEC's with the first string inverters. There are other things I won't admit too also :happyno:
Do you recall the Sunny Boys with no GEC terminal? (heavy red boxes) They had NO terminal for an egc on the DC side, and none for a GEC any where.......just an AC egc.
And many other inverters weren't even made ready for GEC connection. Actually, it took SMA a long time to realize that 2 grounding terminals is not enough, when it was a NEC requirement to run DC GEC's..

 

[c_picard]

Someday I hope to be "notable".

The DC GEC should be connected to the AC GES. Clear as mud. Terminating at a subpanel would not by any stretch fulfill this requirement, if the conductor from the sub to the POI is sized and treated as an EGC. We can terminate the DC GEC on a busbar(though many incentive and rebate programs still require an irreversible crimp), the busbar must also be in the same equipment as the AC GEC termination. I'm curious who the notable person that disagrees is.

"In cases like this the only interpretation that counts is that of the inspector for the AHJ. I would suggest making an appointment with him (or her) and getting their take on it. "

I fully support developing a professional relationship with the AHJ. However, we in the industry have an obligation to educate AHJ's that are not fully up to speed on code req's regarding PV. Understand that these folks are totally overwhelmed with their workload, and unfortunately do not have the time to read ROP's and white papers (Though I would argue that real pros make time to be pros). The code, as I see it, is pretty clear on this matter. The AHJ's have a professional obligation to be every bit as much of an expert on PV as installers, and we should be holding them to that standard. I make allowances for time and $$$ to be at the top of my field, and I think it is fair to expect the same from folks whose salary I am paying.

Other than that, I have no strong feelings on the subject.