The Code reason behind the "return" to full-size Neutral?

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
It might also be worth noting that the NEC has the general provision for sizing feeder neutrals to the calculated load, but AFAIK had no such provision for branch circuit neutrals. So there's a bit of a catch-22 here. Unless the manufacturer gives you a 705.95(B) letter, you need a full size neutral (i.e. same as ungrounded conductors) for the branch circuit. But if the manufacturer can't tell you that because there's a teeny weeny bit of non-sensing current on the neutral, then you need a full size neutral for the branch circuit even if it's a ridiculously teeny-weeny bit. So why should they tell you how much if it makes no difference? (Answer: for feeders, but you get my drift.) I'd note that electric dryers and ranges have the same problem. There's an incredible amount of wasted metal in neutrals out there in the world. Maybe that's the point.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
But I would say that a PV inverter is not utilization equipment, so the circuit it connects to is a feeder, not a branch circuit.

Cheers, Wayne
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
But I would say that a PV inverter is not utilization equipment, so the circuit it connects to is a feeder, not a branch circuit.

Cheers, Wayne
Oh, not this again. Yes, you'd say that, but you'd have a hard slog changing all the AHJs and microinverter manuals that talk about the circuits as branch circuits.
 

Carultch

Senior Member
Location
Massachusetts
Oh, not this again. Yes, you'd say that, but you'd have a hard slog changing all the AHJs and microinverter manuals that talk about the circuits as branch circuits.
Fortunately, most microinverter branch circuits that you'd build today, don't use a neutral anyway, so it's a moot point for them.

The only exception I know about, is the rest of the world, with 230/400V, where microinverters are wired phase-to-neutral on staggered phases. In that case, the neutral would be required to be full size anyway, because in the event that only the A-phase optimizers are running, neutral will carry the full current.

Probably why the NEC only specified reduced neutrals on feeders, but not branch circuits, is that most branch circuits are small enough that the sizing rules govern the neutral and EGC to always equal the phase conductors. The same physical principles should ultimately apply to branch circuits and feeders, since the only difference is the rank of the circuit in the hierarchy of the site's distribution. They both are behind an OCPD that fully protects them.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Oh, not this again. Yes, you'd say that, but you'd have a hard slog changing all the AHJs and microinverter manuals that talk about the circuits as branch circuits.
If you and I have gone through this before, then I agree no need to rehash it. I don't have a good memory for past discussions like that. It's just obvious to me they are feeders, not branch circuits.

As to the AHJs, I would expect them to be able to read and logically interpret the definitions as well as I can. I mean, it's not like anything in Article 690 (or 705) refers to PV system wiring as branch circuits. Of course, if I were doing this professionally, I imagine my expectations in this regard could often leave me sorely disappointed. : - )

Cheers, Wayne
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Of course, if I were doing this professionally, I imagine my expectations in this regard could often leave me sorely disappointed. : - )
Well, I am doing this professionally, and I can assure you that I am indeed sorely disappointed from time to time when I am dealing with inspectors who have a modicum of authority but not a grasp of how electricity works. :D
 
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