690.47

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Before I ask my first question, lets just make sure Im not starting off on the wrong foot. Do I have this right:

690.47(A) Is this for those "AC modules" they mention in the code book but that dont actually exist?
690.47(B) Is this for non-isolating/transformerless inverters?
690.47(C) Is this for isolating inverters?
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Maybe, but not really.

690.47(A) you have correct.

690.47(B): If you ask me, it should consist of only the first paragraph, and the rest of it (referring to inverters) should be moved to 690.47(C). That's how it was in the 2008 code and IMHO should have been left that way. Why the bit about common electrode got added in 2011 I haven't looked into. This would mean that 690.47(B) would apply principally to that rare breed that is not very common but technically under the scope of 690: DC utilization systems with no inverter.

Which leaves...
690.47(C) covering all systems with inverters as a distinct component (i.e. not hidden inside an AC module). Basically if you have an inverter now you have both DC and AC grounding requirements. It makes sense if you take my suggestion of imagining that the last two paragraphs of the preceding section got accidentally put in the wrong place.

Your idea sort of makes sense except that a) the bit referring to ungrounded systems in 690.47(C)(3) in the 2014 code, and b) it doesn't jive with the history of how those three sections once stood for something different. It's sort of a garbled mess now.

So... what's your actual question? :D
 

Carultch

Senior Member
Location
Massachusetts
Maybe, but not really.

690.47(A) you have correct.

690.47(B): If you ask me, it should consist of only the first paragraph, and the rest of it (referring to inverters) should be moved to 690.47(C). That's how it was in the 2008 code and IMHO should have been left that way. Why the bit about common electrode got added in 2011 I haven't looked into. This would mean that 690.47(B) would apply principally to that rare breed that is not very common but technically under the scope of 690: DC utilization systems with no inverter.

Which leaves...
690.47(C) covering all systems with inverters as a distinct component (i.e. not hidden inside an AC module). Basically if you have an inverter now you have both DC and AC grounding requirements. It makes sense if you take my suggestion of imagining that the last two paragraphs of the preceding section got accidentally put in the wrong place.

Your idea sort of makes sense except that a) the bit referring to ungrounded systems in 690.47(C)(3) in the 2014 code, and b) it doesn't jive with the history of how those three sections once stood for something different. It's sort of a garbled mess now.

So... what's your actual question? :D


What is your explanation of 690.47(D)anger?
 
Maybe, but not really.

690.47(A) you have correct.

690.47(B): If you ask me, it should consist of only the first paragraph, and the rest of it (referring to inverters) should be moved to 690.47(C). That's how it was in the 2008 code and IMHO should have been left that way. Why the bit about common electrode got added in 2011 I haven't looked into. This would mean that 690.47(B) would apply principally to that rare breed that is not very common but technically under the scope of 690: DC utilization systems with no inverter.

Which leaves...
690.47(C) covering all systems with inverters as a distinct component (i.e. not hidden inside an AC module). Basically if you have an inverter now you have both DC and AC grounding requirements. It makes sense if you take my suggestion of imagining that the last two paragraphs of the preceding section got accidentally put in the wrong place.

Your idea sort of makes sense except that a) the bit referring to ungrounded systems in 690.47(C)(3) in the 2014 code, and b) it doesn't jive with the history of how those three sections once stood for something different. It's sort of a garbled mess now.

So... what's your actual question? :D

HMMM ok. I agree it is a garbled mess. So the question is, I am just trying to follow the code path for each of the following situations: tramsformerless inverter, transformer inverter, and micro inverter (which I know doesnt have to be its own thing, just bear with me).

1. Ok so the CMP obviously stayed an extra day just to make it as unclear as possible, but I sort of follow how to arrive at the GEC requirements for transformer inverters, but where does the code split and tell me/not tell me that I need a GEC for a transformerless inverter?

2. Why do microinverters (I know at least some are isolating) not have to have an GEC? Maybe they are using the Combined EGC/GEC method, but then how do they get around the "irreversible splice" clause?
 

SolarPro

Senior Member
Location
Austin, TX
1. Ok so the CMP obviously stayed an extra day just to make it as unclear as possible, but I sort of follow how to arrive at the GEC requirements for transformer inverters, but where does the code split and tell me/not tell me that I need a GEC for a transformerless inverter??

That's the new language in 690.47(B): "An ac equipment grounding system shall be permitted to be used...for the ground-fault detection reference for ungrounded PV systems."

This is probably not the best subsection for this, as people like to point out. However, the CMP intended for this language to clarify that a GEC is not required for tranformerless inverters.

The proposed language for 2017 generally improves things related to system grounding. But it's a pretty extensive rewrite.

If you're still on the 2011 NEC, this article provides some guidance regarding ungrounded PV systems:

Ungrounded PV Power Systems in the NEC

Just search the text (command + F) for GEC.
 
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Carultch

Senior Member
Location
Massachusetts
This is probably not the best subsection for this, as people like to point out. However, the CMP intended for this language to clarify that a GEC is not required for tranformerless inverters.

How difficult is it for the code to say?
690.47(E): Listed transformerless inverters with ungrounded DC systems shall not be required to have a grounding electrode conductor.
 
That's the new language in 690.47(B): "An ac equipment grounding system shall be permitted to be used...for the ground-fault detection reference for ungrounded PV systems."

This is probably not the best subsection for this, as people like to point out. However, the CMP intended for this language to clarify that a GEC is not required for tranformerless inverters.

The proposed language for 2017 generally improves things related to system grounding. But it's a pretty extensive rewrite.

If you're still on the 2011 NEC, this article provides some guidance regarding ungrounded PV systems:

Ungrounded PV Power Systems in the NEC

Just search the text (command + F) for GEC.

But what I am not seeing is why systems with isolating inverters are called "systems with AC and DC grounding requirements" and non-isolating inverters are "DC systems" :? ....or is that what everyone else is wondering too?
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
HMMM ok. I agree it is a garbled mess. So the question is, I am just trying to follow the code path for each of the following situations: tramsformerless inverter, transformer inverter, and micro inverter (which I know doesnt have to be its own thing, just bear with me).

First, the technical distinction is between grounded and ungrounded DC systems. Enphase's latest line of inverters, for example, are ungrounded but also have a transformer in them.

My understanding is that the CMP accepted the argument that because UL standards don't require a GEC for an ungrounded inverter, the code needn't require a GEC from the PV system. The entire PV system still needs have equipment grounding which is ultimately connected to earth, but there doesn't need to be a conductor(s) between the inverter and electrode that meets all the requirements of 205.166.

If you ever get the chance, put your clamp meter around the GEC for a larger grounded system: you'll see a bit of current flowing. Not so much for ungrounded systems. Has to do with module frame capacitance, IIRC. So, yes, there is some real reasoning behind a slightly larger, more bonded GEC on grounded systems.

As far as how garbled it is, check out this interesting tidbit from the 2014 ROP:

The change to 690.47(C)(3) is in response to the TCC Directed Task Group
consisting of CMP-4 and CMP-5 members to discuss the conflict between
250.121 and 690.47(C)(3). The change in 690.47(C)(3) from the term
“Grounding Electrode Conductor” to “PV Bonding Conductor” resolves the
conflict with 250.121. The other changes reflect the change from a grounding
electrode conductor to a bonding jumper.

250.121 says that an EGC can't be a GEC, but 690.47(C) says they can be combined.

1. Ok so the CMP obviously stayed an extra day just to make it as unclear as possible, but I sort of follow how to arrive at the GEC requirements for transformer inverters, but where does the code split and tell me/not tell me that I need a GEC for a transformerless inverter

I'd say it doesn't split that way, which is indeed confusing.

The last sentence of 690.47(C)(3) says you can size your GEC for your ungrounded inverter to 250.122. One notable AHJ I work in takes this to mean the whole PV system just needs to be bonded according to 250.122, which I don't have a problem with. OTOH, one interpretation I've seen (in a Solar Pro article), is that the GEC can be smaller but still has to be installed as in 250.64, i.e. unspliced or irreversibly spliced, bonding bushings, etc.. The best argument against this is that the bits in 690.47(B) say that ordinary EGC bonding is permitted.

2. Why do microinverters (I know at least some are isolating) not have to have an GEC? Maybe they are using the Combined EGC/GEC method, but then how do they get around the "irreversible splice" clause?

There's no particular rule for micro-inverters, which aren't defined in the NEC. Enphase's older models had a grounded DC conductor, and thus required a GEC, which their manuals made clear. However their newer models are ungrounded, and the manuals no longer mention a GEC. Plus, they published a whitepaper pointing out that UL said they no longer needed a GEC, which swayed a lot of AHJ's for me.

What is your explanation of 690.47(D)anger?

That's really an unrelated subject. But since you ask, I put it down to three factors: a) confusion over bonding vs. grounding, b) people forgetting that the scope of the NEC does not include preventing/redirecting lightning strikes, which is covered by a different code, and c) a North American fetish with grounding.
 

SolarPro

Senior Member
Location
Austin, TX
How difficult is it for the code to say?
690.47(E): Listed transformerless inverters with ungrounded DC systems shall not be required to have a grounding electrode conductor.

It's not difficult per se; it's just a process. First, someone has to propose this language. Then the CMP has to review it and vote on it. If you officially submit this language now, you could get it queued up for the 2020 NEC; the proposal period for NEC 2017 is closed.

When you consider how cumbersome the Code-making process is, it's not a huge surprise that the results are occasionally suboptimal. The good news is that there are open record for the proposals and the review process. If you're confused about the intent of a revision, you can review the Report on Proposals and Report on Comments.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
But what I am not seeing is why systems with isolating inverters are called "systems with AC and DC grounding requirements" and non-isolating inverters are "DC systems" :? ....or is that what everyone else is wondering too?

The way I see it, that distinction is not made. Any system with an inverter is a "system with AC and DC grounding requirements". The difference is in the DC requirements.

It might help to think that the GEC serves two purposes:
1) to ground grounded conductors
2) to ground equipment grounding conductors and all the parts they bond

A grounded DC system has to meet (1) and (2), but an ungrounded system only has to meet (2). And the grounded conductor has to be connected directly to the GEC, but EGCs can be connected via other EGCs.

Thus:
1) A grounded DC system has to have a GEC run to the point where the grounded conductor is grounded, which is the inverter.
2) An ungrounded DC system merely needs all equipment connected via EGC to the premises GEC, just like anything else in a building supplied by AC power.

Does that make sense?
(Does anyone disagree?)
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
The way I see it, that distinction is not made. Any system with an inverter is a "system with AC and DC grounding requirements". The difference is in the DC requirements.

It might help to think that the GEC serves two purposes:
1) to ground grounded conductors
2) to ground equipment grounding conductors and all the parts they bond

A grounded DC system has to meet (1) and (2), but an ungrounded system only has to meet (2). And the grounded conductor has to be connected directly to the GEC, but EGCs can be connected via other EGCs.

Thus:
1) A grounded DC system has to have a GEC run to the point where the grounded conductor is grounded, which is the inverter.
2) An ungrounded DC system merely needs all equipment connected via EGC to the premises GEC, just like anything else in a building supplied by AC power.

Does that make sense?
(Does anyone disagree?)

I think that that is what the NEC at least implies, but is there any reason why in an ungrounded PV system a ground rod driven at the inverter which is tied to the existing building ground with a large conductor would be contraindicated, other than that it might be an unnecessary expense?
 
The way I see it, that distinction is not made. Any system with an inverter is a "system with AC and DC grounding requirements". The difference is in the DC requirements.

It might help to think that the GEC serves two purposes:
1) to ground grounded conductors
2) to ground equipment grounding conductors and all the parts they bond

A grounded DC system has to meet (1) and (2), but an ungrounded system only has to meet (2). And the grounded conductor has to be connected directly to the GEC, but EGCs can be connected via other EGCs.

Thus:
1) A grounded DC system has to have a GEC run to the point where the grounded conductor is grounded, which is the inverter.
2) An ungrounded DC system merely needs all equipment connected via EGC to the premises GEC, just like anything else in a building supplied by AC power.

Does that make sense?
(Does anyone disagree?)

Yes that makes sense and has pretty much been my thinking - that the grounding requirements are more stringent when we are system grounding than if we were equipment earthing, just because that is the way it generally is in the NEC. Transformerless inverters cant be system grounding so we get to use the "lax" requirements of "normal" methods and connections.
 

SolarPro

Senior Member
Location
Austin, TX
Granted, the language wasn't located optimally, but here's the language from the ROP that clarifies the intent of the addition:

Submitter: Code-Making Panel 4,
Recommendation: Change 690.47(B) and 690.47(C)(3) as follows:
Append a third paragraph to 690.47(B) to read as follows:

An ac equipment grounding system shall be permitted to be used for equipment grounding of inverters and other equipment, and the ground-fault detection reference for ungrounded PV systems.

In the substantiation, the CMP clarifies that the language is intended to address the concerns in Proposal 4-311, which reads:

RECOMMENDATION: Add a new third paragraph as follows:
Ungrounded DC PV arrays connected to utilization equipment with common ac and dc equipment-grounding terminals shall be permitted to have equipment grounding requirements met by the ac equipment-grounding system without the requirement for a dc grounding electrode conductor or grounding system.

SUBSTANTIATION: The first paragraph of 690.47(B), as currently written, applies to stand-alone ungrounded DC PV systems where a new grounding electrode and grounding electrode conductor are required. There is no requirement directly addressing the ungrounded PV array connected to a utility-interactive inverter as allowed by 690.35.

The great majority of ungrounded PV arrays will be connected to utility-interactive inverters and those inverters have common ac and dc equipment grounding terminals. The PV array dc equipment-grounding conductors, when connected to such inverters, have the array dc equipment grounding conductors connected to earth through the ac equipment grounding system and the existing ac grounding system. Additional grounding electrodes and grounding electrode conductors are not required, but may be used.

No doubt it could have been stated more clearly, but this is where does the Code says that a GEC isn't required w/ transformerless inverters.
 
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Garrison

Member
Location
Chicago, IL
On a recent install with a SunnyBoy TL the inspector asked for a DC GEC from the inverter, or an "official" statement that is it not required. I found a piece that Wiles wrote in the IAEI that the inspector has accepted, along with the UL Certificate of Compliance. According to Wiles, if the inverter is transformerless it should not even have a GEC terminal if it is listed to UL 1741. This is supported by the SunnyBoy TL installation manual that labels the ground terminal in the DC disconnect, “For the connection of the DC equipment grounding conductor.”

http://www.nmsu.edu/~tdi/pdf-resources/IAEI Mar_Apr 2012.pdf
 

Carultch

Senior Member
Location
Massachusetts
Exactly. And Wiles was the author of proposal 4-311, which the CMP amended to become the language that made it into NEC 2014.


Strange how Wiles successfully got the counterproductive 690.47(D)anger in the 2014 NEC, but couldn't get a clear language saying that transformerless ungrounded inverters do not require a GEC.
 

SolarPro

Senior Member
Location
Austin, TX
Strange how Wiles successfully got the counterproductive 690.47(D)anger in the 2014 NEC, but couldn't get a clear language saying that transformerless ungrounded inverters do not require a GEC.

Maybe that's because Wiles' proposal for 690.47(D) was rejected. The language that was accepted is courtesy James J. Rogers, Bay State Inspectional Agency.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Maybe that's because Wiles' proposal for 690.47(D) was rejected. The language that was accepted is courtesy James J. Rogers, Bay State Inspectional Agency.

The more I read 690.47 the more confused I get.

For example, Exception No. 2 to 690.47(D) reads, "An array grounding electrode(s) shall not be required if located within 1.8m (6 ft) of the premises wiring electrode". If WHAT is located within 1.8m of the premises wiring electrode?? The array? The grounding electrode that isn't needed because if it were there it would be within 1.8m of the existing electrode?

And in Exception No. 1, "An array grounding electrode(s) shall not be required where the load served by the array is integral with the array. " What is the "load served by the array"? The inverter? The building? What do they mean by "integral"? Dictionary dot com defines integral as:

1. of, relating to, or belonging as a part of the whole; constituent or component: integral parts.


2.necessary to the completeness of the whole:This point is integral to his plan.


3.consisting or composed of parts that together constitute a whole.

4.entire; complete; whole:

I can't make any of those definitions make sense in the context of their sentence. Did they use "integral" just because it sounded smart?

Would it kill them to write in clear English? My freshman English Composition teacher would have ripped them to shreds over this stuff.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
The more I read 690.47 the more confused I get.

For example, Exception No. 2 to 690.47(D) reads, "An array grounding electrode(s) shall not be required if located within 1.8m (6 ft) of the premises wiring electrode". If WHAT is located within 1.8m of the premises wiring electrode?? The array? The grounding electrode that isn't needed because if it were there it would be within 1.8m of the existing electrode?

I'm going with 'an array grounding electrode shall not be required where the premises wiring electrode is within 6ft of the 'as close as practicable' point.' But really, if they're not going to delete this section entirely, they should simply change it to "an additional array grounding electrode shall not be required where the array can be bonded to a premises wiring electrode."


And in Exception No. 1, "An array grounding electrode(s) shall not be required where the load served by the array is integral with the array. " What is the "load served by the array"? The inverter? The building? What do they mean by "integral"? Dictionary dot com defines integral as:

I think they mean those little setups that supply a single luminare on a pole. But I completely agree with...

Would it kill them to write in clear English? My freshman English Composition teacher would have ripped them to shreds over this stuff.
 

SolarPro

Senior Member
Location
Austin, TX
Again, it helps to follow the evolution of the 690.47(D) and read the substantiating comments or talk to someone on the CMP, which we did for our NEC 2014 article:

The requirements found in Section 690.47(D) have been controversial since they were first added to the Code in 2008. (See “Additional Electrodes for Array Grounding,” SolarPro magazine, October/November 2008.) Some industry stakeholders pointed out that the requirements did little to improve system safety and they significantly increased costs, especially on smaller PV systems. Others complained that the section was poorly written, included language ripe for misinterpretation and contained requirements that were difficult to enforce or comply with. As a result, many industry veterans were pleased when this language was removed from NEC 2011. Unfortunately for them, Section 690.47(D) reappears in NEC 2014, only with a twist this time—a one-word change that has inspired a new set of detractors.

Whereas the 2008 version of Section 690.47(D) required “additional electrodes for array grounding,” the 2014 version requires “additional auxiliary electrodes for array grounding.” According to a substantiation in the ROC, the intent of adding the term auxiliary was to signal that “this grounding electrode is not required to be tied into the premises’ grounding-electrode system; and if multiple grounding electrodes are installed, they do not need to be bonded together by a dedicated bonding conductor.” The substantiation concludes by noting that the dc EGC “will serve to bond the electrodes in the PV array together. A separate bonding conductor would be duplicative.”

Not everyone agrees with this assessment. Mike Holt, the founder of Mike Holt Enterprises, is a Code expert and electrical training specialist. According to a 26-minute YouTube video presentation (see Resources), Holt’s opinion is that “690.47(D) needs to be immediately removed from the Code. It is the only Code rule I am aware of that was added to the Code that makes an installation unsafe.”

The safety problem, as Holt sees it, is that the 2014 version of Section 690.47(D) references Section 250.54, “Auxiliary Grounding Electrodes,” meaning that system integrators do not need to incorporate the required auxiliary electrode into the premises’ grounding-electrode system. As a result, in the event of a lightning strike there could be a difference in potential, or voltage, between an auxiliary electrode and the grounding-electrode system. If that occurred, the difference in potential would induce current in the EGC path. Not only is equipment in this path at risk of damage from lightning-induced surges, but also people could be exposed to a shock hazard, either due to direct contact with an inadvertently energized circuit component or due to a side flash, which occurs when lightning jumps from one object to another.

Brooks concurs with Holt’s assessment: “If the AHJ requires an additional electrode on a building with an existing electrode, then you should bond the new electrode to the existing electrode following the requirements of Section 250.53. You should make this bond at ground level, not over the top of the building. Making the bond any place other than ground level is asking for lightning damage.”

Brooks continues: “My basic interpretation is that all buildings with an existing electrode do not require this additional auxiliary electrode because of Exception 2. The building electrode applies to the whole building. So regardless of the physical placement of a ground rod, there is no place on a structure with an electrode that can be farther than 6 feet from the premises’ wiring electrode. An uncontroversial example of this is an Ufer ground that is attached to reinforcing steel in the concrete. A reasonable person would agree that the whole slab is part of the grounding system.”

Bill's interpretation in the final paragraph is noteworthy because he's the one who suggested the language that made it into NEC 2008. It was intended to specifically address situations like pole- or ground-mounted arrays (free-standing structures) that interconnect to a service as separate structure. Since then the subsection has taken on a life of its own that misses the original intent.

The proposed fix in 2017, as I understand it, is to say something like "additionally electrodes are allowed"—not required. Unless we're talking separate structures, where the PV is not integral to the structure where it interconnects. If the PV is installed at a separate structure, that structure should have a GEC.

This excerpt from our grounding compendium article is also relevant:

In the 2008 NEC, Section 690.47(D) requires “additional electrodes for array grounding” at all ground- and pole-mounted PV arrays; the electrode must be directly connected to the array frame or structure using a GEC sized per Section 250.166. While this requirement was deleted during the 2011 cycle of revisions, this should not be interpreted as a signal that PV arrays do not require additional electrodes. Section 250.32 requires that a grounding electrode be installed at structures with feeders. As defined in Article 690, a PV array includes a support structure and foundation, and thus requires an electrode. Furthermore, the code-making panel responsible for Article 690 approved language for the 2014 NEC that explicitly requires additional electrodes for all ground- and pole-mounted systems, in accordance with Section 250.52.

For a large ground-mounted system, the question becomes: What portions of the system are considered separate structures or arrays and thus require grounding electrodes? Many system engineers choose to install an approved electrode, such as a ground rod, for each row of a ground-mounted PV array. While the piles or piers that support the racking structure provide an electrically conductive connection to ground, they typically do not meet the Code requirements for use as grounding electrodes. A critical difference between Section 690.47(D) (as it appears in NEC 2008 and NEC 2014) and Section 250.32 is that the former requires a structure-specific GEC sized according to Section 250.166, whereas the latter requires only the connection of an EGC sized in accordance with Section 250.122 to equipment, structures, frames and the grounding electrode.

Ladd explains PowerSecure’s conservative design approach for ground-mounted arrays: “In addition to the Code-required equipment grounding, we attach each section of racking together with a bare solid copper conductor or similar, and attach each row of racking to a buried bare 1/0 copper wire. There is no Code requirement for this additional grounding. We do this to ensure that there is no difference in potential between any portion of the array and also to provide a flow path for lightning energy.”
 
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