upsizing EGC due to voltage drop

[ellehktrick]

Hi folks, my jurisdiction is now on NEC 2020 and one of the curious changes is in article 690.45. Previously in NEC 2017 this article allowed you to forgo upsizing PV source and PV output circuit EGCs if you upsized ungrounded conductors for voltage drop (something 250.122 requires of all other EGCs). In NEC 2020 this articles changes it to all PV system circuits.

I heard that the rational for forgoing this upsizing in 2017 NEC was because the DC ground fault detector would work even if the impedence of the EGC system was higher than normal. If that is true then why would NEC 2020 allow this "exemption" for AC side circuits that don't have the same ground fault protection?

Also it leaves me confused about what to do with the AC grounded conductor (neutral). Since the PV system is balanced I typically size my grounded conductor to the smallest it can be. This is driven by article 250.24(C) which lets us size the grounded conductor according to table 250.122. So if I read that literally I would need to upsize that grounded conductor for voltage drop even though I am not upsizing my EGC due to the "exemption" in 690.45 (which only specifies EGCs not grounded conductors as well).

Does anyone have any thoughts of clarity or notice any holes in what I wrote? I'm leaning towards just upsizing due to VD on the AC side like I have been to play it safe but if anyone can instill some confidence in me it would be great not to use all that AL.

thanks,

 

[ggunn]

Hi folks, my jurisdiction is now on NEC 2020 and one of the curious changes is in article 690.45. Previously in NEC 2017 this article allowed you to forgo upsizing PV source and PV output circuit EGCs if you upsized ungrounded conductors for voltage drop (something 250.122 requires of all other EGCs). In NEC 2020 this articles changes it to all PV system circuits.

I heard that the rational for forgoing this upsizing in 2017 NEC was because the DC ground fault detector would work even if the impedence of the EGC system was higher than normal. If that is true then why would NEC 2020 allow this "exemption" for AC side circuits that don't have the same ground fault protection?

Also it leaves me confused about what to do with the AC grounded conductor (neutral). Since the PV system is balanced I typically size my grounded conductor to the smallest it can be. This is driven by article 250.24(C) which lets us size the grounded conductor according to table 250.122. So if I read that literally I would need to upsize that grounded conductor for voltage drop even though I am not upsizing my EGC due to the "exemption" in 690.45 (which only specifies EGCs not grounded conductors as well).

Does anyone have any thoughts of clarity or notice any holes in what I wrote? I'm leaning towards just upsizing due to VD on the AC side like I have been to play it safe but if anyone can instill some confidence in me it would be great not to use all that AL.

thanks,

The code lets you size the neutral in accordance with 250.102, not 250.122 (that changed in 2020) as shown in 705.28(C(2). My opinion is that whether or not it needs to be upsized when the CCCs are bigger because of Vd is moot because the inverter output circuits are PV system circuits.

Is this a three phase AC interconnection? If so, one thing to check is whether your inverters require a neutral at all.

 

[jaggedben]

I haven't looked up the NPFA documentation on the 690.45 change, but I would guess you are overreading the change as applying to AC circuits. My guess is that this was done to extend the rule to DC-to-DC converter (i.e. 'optimizer') output circuits, which have been included in the article 690 definition of 'PV System Dc Circuits' for a couple cycles. Nowhere does the code define AC circuits as PV system circuits. Although admittedly this is a grey area that the code consistently fails to be clear on.

As far as AC circuits though, you may want to take note of the new exception to 250.122 (B) which lets a qualified person determine the size of the EGC necessary to provide an effective ground fault current path.

 

[wwhitney]

I haven't looked up the NPFA documentation on the 690.45 change, but I would guess you are overreading the change as applying to AC circuits. My guess is that this was done to extend the rule to DC-to-DC converter (i.e. 'optimizer') output circuits, which have been included in the article 690 definition of 'PV System Dc Circuits' for a couple cycles. Nowhere does the code define AC circuits as PV system circuits. Although admittedly this is a grey area that the code consistently fails to be clear on.

I considered the possibility that the phrase 'PV System Circuits' in 690.45 was meant to be a synonym for 'PV System DC Circuits.' But if you look at (2020) Article 690, while 'PV System DC Circuits' is the defined phrase and occurs much more often, the phrase 'PV System Circuits' does occur in multiple places, and generally for rules that can include not just PV System DC Circuits but also Inverter Output Circuits. E.g. 690.8(A)(1) and 690.12.

However, it would be clearer if 'PV System Circuits' were a defined term.

Cheers, Wayne

 

[Carultch]

The code lets you size the neutral in accordance with 250.102, not 250.122 (that changed in 2020) as shown in 705.28(C(2).

There is a part of 250.102 that redirects you to 250.122, once your circuit classifies as a feeder or branch circuit (i.e. load side of an OCPD that protects it). Essentially, the idea is that the neutral needs to at least be as large as the green wire that routes with the circuit, whatever you would call it. Whether it is an EGC per 250.122 or an SSBJ per 250.102, the green wire size governs the minimum white or gray wire size. Unless the neutral current governs it otherwise.

The directing you first to 250.102 needs to say what it says, for purposes of circuits like service conductors and transformer secondary conductors, where the circuit is "not yet protected" at its ampacity. However, most of the time, you will end up following 250.122 eventually anyway, for this calculation.

 

[jaggedben]

I considered the possibility that the phrase 'PV System Circuits' in 690.45 was meant to be a synonym for 'PV System DC Circuits.' But if you look at (2020) Article 690, while 'PV System DC Circuits' is the defined phrase and occurs much more often, the phrase 'PV System Circuits' does occur in multiple places, and generally for rules that can include not just PV System DC Circuits but also Inverter Output Circuits. E.g. 690.8(A)(1) and 690.12.

However, it would be clearer if 'PV System Circuits' were a defined term.

Cheers, Wayne

Yeah, my position is that the NEC is just genuinely disorganized and inconsistent on this. In the example at hand, nothing you point out eliminates the possibility that 'PV System Circuits' in 690.45 was meant to be a synonym for 'PV System DC Circuits' and that some author or editor failed to realize that leaving out the 'DC' part makes it ambiguous. Again, I haven't looked up the documentation.

 

[wwhitney]

Yeah, my position is that the NEC is just genuinely disorganized and inconsistent on this.

So, while the other uses of the term "PV System Circuits" in 690 are consistent, in the case of 690.45 I think you are right.

I looked at the 2020 NEC First and Second Draft reports, because you can read those in Terraview at nfpa.org. In the first draft, 690.45 had two sections, the second section was the sentence about EGC size and voltage drop, and that section was titled "PV System DC Circuits". The first section was "PV System AC and DC Circuits".

However, the first draft also made a big change to 250.122 and switched to EGC size based on ungrounded conductor size, not OCPD size. So then some of the second draft comments on 690.45 were apparently that the bit about EGC and voltage drop was now moot. But in the second draft 250.122 reverted to its familiar form where EGC is based on OCPD size (for better or worse).

Anyway, in the second draft report, the section titles in 690.45 got deleted, and so the information that the last sentence was restricted to PV System DC Circuits was lost. I bet that wasn't intentional.

Cheers, Wayne

 

[pv_n00b]

Anyway, in the second draft report, the section titles in 690.45 got deleted, and so the information that the last sentence was restricted to PV System DC Circuits was lost. I bet that wasn't intentional.

Cheers, Wayne

There was a public comment on the 2023 NEC 690.45 to remove the sentence about not upsizing EGCs when upsizing the CC conductors due to voltage drop. The reasoning given in the comment was that both AC and DC EGCs need to be upsized. In rejecting this comment the CMP4 response would seem to indicate that they are applying the exception to EGC upsizing to both the AC and DC EGCs.

This Code requires a minimum ampacity for conductors. The size of the equipment grounding conductor (EGC) is based on the overcurrent device protecting the properly-sized circuit. Where conductors are upsized for voltage drop, the overall impedance of the fault circuit is decreased. Upsizing AC circuit conductors in PV systems for performance reasons should not be penalized by a requirement to upsize the EGC. While there may be other reasons to do this for other types of systems (beyond the scope of CMP4), the electrical systems on the ac and dc side of PV systems do not require such measures. This is why Article 690 modifies the general rule in Article 250.

 

[wwhitney]

Ah, so it's a disagreement between CMP 4 (in charge of Article 690) and CMP 5 (in charge of Article 250).

Cheers, Wayne

 

[pv_n00b]

Ah, so it's a disagreement between CMP 4 (in charge of Article 690) and CMP 5 (in charge of Article 250).

Cheers, Wayne

That would never happen. It's all butterflies and flowers in code town. ;-)

 

[jaggedben]

Ah, so it's a disagreement between CMP 4 (in charge of Article 690) and CMP 5 (in charge of Article 250).

Cheers, Wayne

Makes sense. It's happened before, which is how we got 250.25. According to a moderator here if I recall correctly.

 

[Electrical Geek]

I think that it is trying to say any circuits within the pv system, doing their best to cover everything. (this is just my opinion, however)

 

[jaggedben]

I think that it is trying to say any circuits within the pv system, doing their best to cover everything. (this is just my opinion, however)

But 'within the PV system' just as vauge as 'PV system circuits'. And if available fault current, fault detection, and energization are primarily governed by the primary source then it doesn't make much sense safety-wise to call inverter output circuits PV systems conductors. The NEC is just a mess on this and as alluded to above, probably deliberately so.

 

[ggunn]

Right or wrong, I treat every conductor from the modules to the point of interconnection as components of PV system circuits.

 

[HoosierSparky]

OK, now here is where I get confused. 250.122 says to size the EGC for the size of the OCPD protecting the circuit. For a PV CIRCUIT, the OCPD could be 40A on a 200A SES. Per the 250.122 table, the EGC should be #10cu. WHY are a lot of AHJ's requiring #6? If the NEC wants the EGC at the array's sized to the MCB at the SES, why not just say so?

 

[ggunn]

OK, now here is where I get confused. 250.122 says to size the EGC for the size of the OCPD protecting the circuit. For a PV CIRCUIT, the OCPD could be 40A on a 200A SES. Per the 250.122 table, the EGC should be #10cu. WHY are a lot of AHJ's requiring #6? If the NEC wants the EGC at the array's sized to the MCB at the SES, why not just say so?

IMO they are considering the risk of physical damage.

 

[HoosierSparky]

IMO they are considering the risk of physical damage.

But that doesn't address WHY go so large if #10 is all that is required by the table. 690.46 states conductors SMALLER that #6 shall comply with 250.120(C) and that just says the EGC shall be protected. The question remains as to why and how does the AHJ's require a #6 bare copper.

 

[ggunn]

But that doesn't address WHY go so large if #10 is all that is required by the table. 690.46 states conductors SMALLER that #6 shall comply with 250.120(C) and that just says the EGC shall be protected. The question remains as to why and how does the AHJ's require a #6 bare copper.

You are tilting at windmills. Ours is not to reason why; ours is to design it to the AHJ's specs or fail the inspection.

 

[wwhitney]

The question remains as to why and how does the AHJ's require a #6 bare copper.

I think it may be a holdover from when a PV array required both a GEC and an EGC, and the requirements of 250.64(B) for GECs.

The common practice of using bonding bushings all over the place in PV installs may be similarly a holdover from when the EGC was also a GEC.

Cheers, Wayne

 

[HoosierSparky]

I get it. I really do. However, what code section is the AHJ's hanging their hat on?