Terminating the neutrals

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Nutmegger

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Fairfield County, Connecticut
Saw a job done by a Craigslist "electrician"... :rant:
A sub installed next to the service panel.

All the homeruns originate through the main panel knockouts.
Only the ungrounded conductors were brought from the main into the sub, through a short EMT nipple, and terminated at the breakers in the sub.

All the neturals were terminated in the main, effectively in a different panel from where the ungrounded conductors originate.
I know it is wrong, but I can't come up with the proper code reference.

300-3 (b) does not refer to a panelboard -- only to "raceway, cable tray, trench, cable, or cord"
210.4 AFAIK is only about MWBC's, but not every circuit is an MWBC.

Any thoughts?
 
My first thought was that the wiring sounded like that which I have seen in a transfer switch.

gentran-vinatage-models-manual-transfer-switch-wiring-diagram-1.gif
 
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Thanks Mark
Comparing it to a portable genny transfer switch does put it in perspective.
The installation that I saw looked REALLY sloppy, which is what made me question the qualification of the person who did it.

I was also thinking of practical reasons -- it is much easier to troubleshoot a circuit when the neutral originates in the same enclosure as the ungrounded conductor, and stays with that conductor.
"Staying with it" [300.3 (B)] and, and originating for MWBC's [(210.4)] are already in the code, so I was thinking that it was mandatory for ANY circuit. But perhaps not!
Thanks for clarifying it.
 
Nutmegger said:
Thanks Mark
Comparing it to a portable genny transfer switch does put it in perspective.
The installation that I saw looked REALLY sloppy, which is what made me question the qualification of the person who did it.

I was also thinking of practical reasons -- it is much easier to troubleshoot a circuit when the neutral originates in the same enclosure as the ungrounded conductor, and stays with that conductor.
"Staying with it" [300.3 (B)] and, and originating for MWBC's [(210.4)] are already in the code, so I was thinking that it was mandatory for ANY circuit. But perhaps not!
Thanks for clarifying it.
Click to expand...

Well, I could be totally wrong and missing something, too.

But, I did take a pretty good look through the book and couldn't find any article violated by such an installation.
 
K8MHZ said:
Technically, that is a good question.

I can't think of a reason the neutrals must be in the same panel as the breakers. How would moving them change their function?

It sounds like a funky installation, but I don't see any hazard with it.
Click to expand...

I can't cite code chapter and verse, but from a physics point of view:

Provided the supply conductors to the subpanel and all of the hot branch circuit conductors pass through the same conduit nipple between the main and the sub, there won't be a problem. However, if the supply conductors were to pass through one nipple, and the branch conductors, current flow wouldn't cancel out, and the possibility of inductive heating of the conduit nipple(s) exists.

When the neutral and the hot conductor(s) are in the same conduit, their magnetic fields cancel, and no inductive heating can take place. What if there's no neutral in the circuit, you say? Then the out-of-phase hot conductors' magnetic fields cancel just the same. No field, no possibility for heating.

Genny transfer switch banks work because the white wire carries the unbalance in current between the two hot phases. All those wires are in the same (flex) conduit, and so the magnetic fields cancel. I believe the neutral on those prewired genny panels is typically larger than the individual branch circuit conductors, yes?

I do know that it's somewhere in the NEC that neutral conductors must originate from the same panel as the hot wires in a circuit. It's also just a darn good idea from a physics standpoint. Also makes troubleshooting easier for the next person.


SceneryDriver
 
I couldn't find anything about the neutrals having to originate from the same panel.

Also, how is the sub panel any different than a switch box with several switches and no neutral in the switch box? I have seen hundreds in metal conduit and boxes and have never heard of any problems with inductive heat.

The neutral in the transfer box is larger, but it goes from the genny plug terminal through the box and lands on the panel neutral. None of the individual neutrals are in the transfer box.
 
SceneryDriver said:
I can't cite code chapter and verse, but from a physics point of view:

Provided the supply conductors to the subpanel and all of the hot branch circuit conductors pass through the same conduit nipple between the main and the sub, there won't be a problem. However, if the supply conductors were to pass through one nipple, and the branch conductors, current flow wouldn't cancel out, and the possibility of inductive heating of the conduit nipple(s) exists.

When the neutral and the hot conductor(s) are in the same conduit, their magnetic fields cancel, and no inductive heating can take place. What if there's no neutral in the circuit, you say? Then the out-of-phase hot conductors' magnetic fields cancel just the same. No field, no possibility for heating.

Genny transfer switch banks work because the white wire carries the unbalance in current between the two hot phases. All those wires are in the same (flex) conduit, and so the magnetic fields cancel. I believe the neutral on those prewired genny panels is typically larger than the individual branch circuit conductors, yes?

I do know that it's somewhere in the NEC that neutral conductors must originate from the same panel as the hot wires in a circuit. It's also just a darn good idea from a physics standpoint. Also makes troubleshooting easier for the next person.


SceneryDriver
Click to expand...

Found the part about induction heating:
300.20
(A) Conductors Grouped Together. To minimize induction heating of ferrous metallic raceways and enclosures, and to maintain an effective ground-fault current path, all conductors of a circuit must be installed in the same raceway, cable, trench, cord, or cable tray.
 
FREEBALL said:
what about shared neutral circuits ??
Click to expand...

Shared neutral circuits (MWBCs) still have to follow this rule. Where all three conductors (in the case of 120/240) are in the same raceway there is no net current. Where the MWBC splits into seperate 120V circuits with individual neutrals, the current is still balanced. And the third wire is no longer required to be present because it would carry no current on that segment. (Carefully not saying "branch".)
The Code explicitly acknowledges that an MWBC can have non-MW extensions and that you can consider the whole thing as one circuit or as individual circuits depending on the context of the rule being applied.

Tapatalk!
 
And for the case of generator ATS or MTS setups, ideally either the hot and neutral currents end up traveling in the same raceway or the hot side will go out in one raceway and the switched hot will come back through the same raceway while the neutral travels a different path.
A "switch leg" which also carries the current carrying neutral in the same run can have unbalanced current, as can the traveler run of a three-way.
I really appreciate the Canadian limitation of the induction rule to 200A or more to avoid the pain of those edge cases.

Tapatalk!
 
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