Ask Me Help Desk - Subpanel Neutral Wiring

I just helped my son install a new Guardian generator that came with a subpanel containing an automatic transfer switch. I have a question about the neutral wires the panel came with. First let me describe the subpanel:

The subpanel has a 70 amp automatic transfer switch, which is fed by either the generator power or the utility power through a 70 amp 2 pole breaker in the main (house) distribution panel. The subpanel has a #6 ground wire to connect back to the ground/neutral bus in the main panel. The subpanel also has a #4 neutral wire connected to its neutral bus and this wire also connects back to the ground/neutral bus in the mail panel. The subpanel has 14 circuits with breakers (some are 2 pole) with hot wires already connected to each breaker (sized appropriately for the breaker size) – these hot wires are to be connected to the hot wires coming into the main panel, using wire nuts, after they are removed from the associated breaker in the main panel. This transfers the circuit from the main panel to the subpanel circuit controlled by the automatic transfer switch.

But my question is about the neutral wires. Each of the 14 circuits in the subpanel has an appropriately sized white neutral wire already connected to the subpanel neutral bus bar. These are brought over through the same conduit as the 14 hot wires to the main panel. The question is what to do with them in the main panel? I saw no reason to disconnect the neutral wire coming in to the main panel from a circuit to be transferred to the subpanel from the main panel neutral/ground bus bar. I therefore connected all 14 neutral wires to the main panel neutral/ground bus bar, the same as the #4 neutral wire between the main and subpanel. Was I instead supposed to connect each of the wires to the incoming neutral wire for each circuit after disconnecting that wire from the main panel neutral bus? If so, why? It would seem that electrically, both the main and the subpanel neutral bus bars are identical. By removing the incoming neutral wire from the main neutral bus and wiring in (using wire nuts) a “jumper” to the subpanel neutral bus, I would just be introducing another point of potential failure in the wire nut connection, plus cluttering up the main panel.

I would appreciate your thoughts on this issue.

I agree with your summation. And since the neutral is not broken by the transfer switch, I tend to agree with you. But I, like you await the answer from someone with knowledge on this installation. I also am about to install a transfer panel for a standby generator. If you get your answer somewhere other than here, please post it for others to see.

Good luck.

I did find another answer in another forum that appears relevant:

Neutral wiring for 16-circuit transfer switch - Ziller Electric Inc | Interactive Guardian Generator Forum

But I would appreciate more opinions. Basically it seems that the extra small neutral wires are electrically redundant, but here seems to be the main reason for including those wires in the provided conduit:

“The only reason for doing anything at all with the smaller gauge individual neutral wires is because the current carrying phase conductors cannot legally travel through a raceway without its associated neutral conductor(s). This rule is only waived on light switches.”

It is interesting to not that of the 14 circuits provided in the subpanel, 6 of them (3 240 volt) did not have associated neutral wires because they are 2 pole circuits. Since only the 120 volt circuits had the associated neutral wires, converting any of those six circuits to 120 volt circuits should also require a neutral due to the above quoted rule. In my case, I did convert one 240 volt circuit to two 120 volt circuits, but I didn't bother to run any more already redundant neutral wires.

You are making great points, but then code is written for reasons many don't understand, but follow anyway. I think that you need to follow the code, redundant as it may be. I'll check out the link...
Thanks for keeping it up to date.

Note that in my initial question, I stated that there were 14 smaller neutral wires in question. This is not correct. There were only eight. As stated above the other six circuits were for three 240 volt circuits which did not require a neutral.

As another comment, the Ziller Electric forum noted above is excellent for information regarding generator and transfer switch installations. There was one thread:

Replace 240V breaker with two 120's? - Ziller Electric Inc | Interactive Guardian Generator Forum

Which tends to contradict the one noted above, in that the replier states that when converting 240 volt circuits to 120 volt circuits, he states that you SHOULD run an extra neutral wire. So on one hand, they state the neutral is redundant and unnecessary, and the other states they are necessary. It seems to me that it is totally unnecessary, other than to satisfy the lack of exception in the code.

Ray

Quote:

Originally Posted by Missouri Bound

You are making great points, but then code is written for reasons many don't understand, but follow anyway. I think that you need to follow the code, redundant as it may be. I'll check out the link....
Thanks for keeping it up to date.

When you read the first link, they state that you need not connect the incoming circuit neutral to the subpanel neutral bus, but rather leave it connected to the main panel neutral bus. Then just connect the smaller neutrals between the busses in the subpanel and main panel. These smaller neutrals are then just more wires paralleling the large #4 neutral.

So adding more neutrals for converting 240 volt circuits to 120 volts circuits seems ridiculous. If the neutrals only connect the two busses in each panel, all they do is share a bit of the total neutral current.

I would certainly like to hear the argument for that part of the code, but it seems there should have been an exception similar to the one for light switches.

And I have a question as well... if you don't switch the neutral, aren't you feeding power back over the neutral wire? Doesn't it become part of the generator circuit?

Quote:

Originally Posted by Missouri Bound

And I have a question as well....if you don't switch the neutral, aren't you feeding power back over the neutral wire? Doesn't it become part of the generator circuit?

I'm neither an electrical contractor nor an electrical engineer, but as a mechanical engineer I happen to have quite a few years of residential electrical experience. So I'm not the best person to offer an opinion on your questions.

However, from what I remember seeing in the generator manual, the neutral IS part of the generator circuit, isolated from ground at the generator, but that part of the circuit is broken when the ATS is in the utility position. So if I'm understanding your question correctly, that part of the neutral "extension" at the generator is irrelevant. When the generator is providing power, and the hot wires are isolated from the utility hot wires by the ATS, the only connection to the utility power is through the neutral, but that is grounded at the main panel. So unless I am not understanding your question properly, I don't see an issue.

Ray

Some food for thought

300.3 Conductors
(B) All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).

Sadly (B)(1) through (B)(4) are quite specific. Even though (B)(4) deals with a similar situation to yours it cannot be applied because of how specific it is. If you did run just one common neutral to the main panelboard it would then be a multi-wire branch circuit and another code would come into play.

210.4 Multiwire Branch Circuits
(A) General
Branch circuits recognized by this article shall be permitted as multiwire branch circuits. A multiwire branch circuit shall be permitted to be considered as multiple circuits. All conductors of a multiwire branch circuit shall originate from the same panelboard or similar distribution equipment.

That last sentence it the problem, if you ran a common neutral to the main panel and then split it out through use of the main panel's neutral bar then the neutrals are originating from there and not the transfer panel.

Quote:

Originally Posted by Tev

Some food for thought

300.3 Conductors
(B) All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).

Sadly (B)(1) through (B)(4) are quite specific. Even though (B)(4) deals with a similar situation to yours it cannot be applied because of how specific it is. If you did run just one common neutral to the main panelboard it would then be a multi-wire branch circuit and another code would come into play.

210.4 Multiwire Branch Circuits
(A) General
Branch circuits recognized by this article shall be permitted as multiwire branch circuits. A multiwire branch circuit shall be permitted to be considered as multiple circuits. All conductors of a multiwire branch circuit shall originate from the same panelboard or similar distribution equipment.

That last sentence it the problem, if you ran a common neutral to the main panel and then split it out through use of the main panel's neutral bar then the neutrals are originating from there and not the transfer panel.

I appreciate your comments and information, and since you are familiar with the codes, I would like clarify what did, and how it applies to the code.

What I conclude from your code quotations, if I am reading them correctly, is that each circuit brought into the main panel and extended and transferred to the ATS subpanel should have both the hot wire AND the neutral wire extended to the subpanel. If that is the case, then the current returning to ground for that circuit would be through the extended neutral to the subpanel neutral bus, then back through the #4 neutral from the subpanel bus to the main panel bus, which is grounded. Is that correct?

If that is correct, it still seems like that is an inferior connection method since a new wire-nutted neutral connection is required in the main panel, rather than a direct connection to the main panel neutral bus - which would seem to accomplish the same connection to ground. When connecting the circuit neutral per the code (again, if I am reading it correctly), that neutral current has to pass through four additional connections (the wire nut, the connection at subpanel neutral bus, and the subpanel neutral bus connection for the #4 wire, and the main panel neutral bus connection for the #4 wire) instead of the one direct connection at the main panel neutral bus. Plus, the extra wire-nutted neutral connections make for a more messy main panel installation.

In addition to all of this, it seems that the code (300.3B above) is also saying that all GROUNDS should also be brought over to the subpanel. Yet there was no provision for any of the separate grounds to be brought over. There was one #6 ground wire (insulated green) from the subpanel, which was connected to the main panel neutral/ground bus.

I have to question the logic of these requirements from both a practical and a scientific perspective.

I neither agree nor disagree with you, that's the inspector's job. :D I would suggest checking local codes and asking the power company if they have any requirements for standby systems. The NEC has a whole page they call Article 702 that does a good job of saying use the proper transfer equipment and good judgment.

I wouldn't worry about the grounding conductors though, they seem to be covered by 300.3(B)(3) which I won't quote here because it only references to 250.130(C) which says that equipment grounding conductors for branch circuit extensions can go to the service equipment enclosure. Assuming your main breaker is in the panel and serves as the main disconnect then that is a service equipment enclosure.

Quote:

Originally Posted by Tev

I neither agree nor disagree with you, that's the inspector's job. :D I would suggest checking local codes and asking the power company if they have any requirements for standby systems. The NEC has a whole page they call Article 702 that does a good job of saying use the proper transfer equipment and good judgment.

I wouldn't worry about the grounding conductors though, they seem to be covered by 300.3(B)(3) which I won't quote here because it only references to 250.130(C) which says that equipment grounding conductors for branch circuit extensions can go to the service equipment enclosure. Assuming your main breaker is in the panel and serves as the main disconnect then that is a service equipment enclosure.

Thank you very much for your comments. That Article 702 sounds interesting to read. I'll see if I can perhaps locate it on the internet.

Thanks again,

Ray