Reduced Neutrals

[Grouch1980]

Hi,
Are reduced neutrals allowed in NYC? I have an existing feeder serving a lighting and receptacle panel, and it has a reduced neutral. We're relocating the panel, thereby extending the feeder, however I was told that in NYC that feeder cannot have a reduced neutral. I calculated the unbalanced current on that neutral, and we're way below its ampacity. So technically it works, but code-wise, does anyone know of any restrictions?

I found nothing in the NYC amendments that prohibits it.

 

[Elect117]

220.61

I am not in NYC, but if you didn't find anything prohibiting it, that is the section to use.

 

[suemarkp]

How do you know what the imbalance will be? Receptacle loads are random. Lighting on one leg can be switched off. In the NEC, the neutral for a panel with only 120V loads generally needs to have the same ampacity the same as the ungrounded conductors unless the feeder is over 200A in which a factor can be applied. Table 250.122 also provides for a minimum size of the neutral even if its load is minimal.

If you had some 240V only loads, that load could be subtracted from the neutral because it is impossible for them to affect it. If the ungrounded's are oversized, but the neutral is sized to the breaker, that seems OK.

How reduced is this neutral, and what size are the ungrounded conductors and the upstream breaker?

Now, I have no idea if New York has additional restrictions.

 

[Tainted]

Hi,
Are reduced neutrals allowed in NYC? I have an existing feeder serving a lighting and receptacle panel, and it has a reduced neutral. We're relocating the panel, thereby extending the feeder, however I was told that in NYC that feeder cannot have a reduced neutral. I calculated the unbalanced current on that neutral, and we're way below its ampacity. So technically it works, but code-wise, does anyone know of any restrictions?

I found nothing in the NYC amendments that prohibits it.

I don't think it's prohibited, in fact NYC permits it in residential installations for 1000kVA service filing, see here:
https://www.nyc.gov/assets/buildings/rules/1_RCNY_4000-01.pdf

(C) For residential installations, the calculations justifying a de-rating of the neutral must be submitted.

Weird thing it doesn't explicitly say for anything other than residential installations

 

[electrofelon]

I love reducing neutrals. I don't think I've ever seen over 30-40 amps on a service or feeder neutral, even on a bigger buildings with a 1000 amp service.

 

[LarryFine]

Weird thing it doesn't explicitly say for anything other than residential installations

Perhaps because non-residential loads tend to be better balanced.

Or maybe because they always require neutral-load calculations.

 

[Tainted]

I love reducing neutrals. I don't think I've ever seen over 30-40 amps on a service or feeder neutral, even on a bigger buildings with a 1000 amp service.

I honestly don't even think I've ever seen Con-Ed reduced their neutrals. Maybe they don't want to take any chances with unexpected harmonics.

 

[LarryFine]

I don't think I've ever seen over 30-40 amps on a service or feeder neutral, even on a bigger buildings with a 1000 amp service.

That's because the rest is traveling on the water pipe.

 

[Tainted]

That's because the rest is traveling on the water pipe.

lol, yea and maybe some of those 3rd order harmonics along with it

 

[Open Neutral]

I love reducing neutrals. I don't think I've ever seen over 30-40 amps on a service or feeder neutral, even on a bigger buildings with a 1000 amp service.

What about the increased harmonic content of switched supplies in everything except the toaster?

 

[electrofelon]

What about the increased harmonic content of switched supplies in everything except the toaster?

I think that is pretty much a myth, I haven't seen it, I think power supplies are pretty "clean" these days.

 

[Elect117]

I think that is pretty much a myth, I haven't seen it, I think power supplies are pretty "clean" these days.

It does happen, but it is less likely an issue on a single phase service. Without getting into the weeds of it, the increased heating effects it can have are less likely an issue when the power supplies are a small portion of the service's general load. Kinda like having a small amount of unbalance at any given time.

It really shows up in 3ph industrial applications where the service size and the amount of variable speed drives start to impact the total harmonic distortion at the service. Then the heat can start to wear on motors faster or lead to nuisance tripping of overload elements.

It would be really uncommon to have a bunch of bitcoin farming units in a apartment that impacted the total distortion enough to effect the service or feeder circuits.

 

[electrofelon]

It does happen, but it is less likely an issue on a single phase service. Without getting into the weeds of it, the increased heating effects it can have are less likely an issue when the power supplies are a small portion of the service's general load. Kinda like having a small amount of unbalance at any given time.

It really shows up in 3ph industrial applications where the service size and the amount of variable speed drives start to impact the total harmonic distortion at the service. Then the heat can start to wear on motors faster or lead to nuisance tripping of overload elements.

It would be really uncommon to have a bunch of bitcoin farming units in a apartment that impacted the total distortion enough to effect the service or feeder circuits.

Perhaps where there are a lot of VFD's, I dont have any experience in those situations where the majority of load is VFDs's. Have measured on 3 phase branch circuits and feeders with mostly "electronic stuff" and never seen anything noteworthy. Balanced LED lighting circuits might see a couple amps on the neutral on a fully loaded circuit.