Does it make a difference if Neutral and Ground Busbars are shared on 120/240 VAC Panel when I ad a Subpanel?

I

Installer

Senior Member
Location
DesMoines, Washington
I'm trying to help a friend install a 120/ 240 Subpanel of 1 120/240 main Panel Most of my experience is with my employer, which has strict rules.
When I started to draw up the subpanel connections, I noticed that the Neutral bar on the Main Panel has Ground connections and the Ground bar has neutral connections.
Since the two should be bonded together, perhaps it doesn't make a difference.
But if that were true why bother running a separate neutral and ground to the new Subpanel?
What do I not understand?
Thank you in advance


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Installer said:
When I started to draw up the subpanel connections, I noticed that the Neutral bar on the Main Panel has Ground connections and the Ground bar has neutral connections.
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I don't see a "ground bar". I see only several sections of neutral bar.

Also please update your profile to include your occupation. Thanks.
 
readydave8 said:
Are you asking why grounds and neutrals are together at service disconnect, and separate after service disconnect?
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I think he was asking about neutrals and EGC conductors being mixed on both the ground and neutral bars of a panel where the bars are bonded. I have seen this a lot and I don't think that in and of itself that it is a problem until you want to install something ahead of it, like an ATS.
 
ggunn said:
I think he was asking about neutrals and EGC conductors being mixed on both the ground and neutral bars of a panel where the bars are bonded.
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But that is not what the picture shows. The picture show two (actually 4) bars that are insulated from the case, with a busbar between them that has a bonding screw to the case. Those are both neutral bars. There are no ground bars.

If you had one neutral bar insulated from the case, one ground bar mounted to the case, and a MBJ connecting the neutral bar to the case, then it would be a violation to land a neutral conductor on the ground bar. As the neutral current path would then be through the case. In the picture in the OP, the neutral current path is only through terminal bars and busbars, regardless of which terminal bar you land the neutral on.

Cheers, Wayne
 
So
ggunn said:
I think he was asking about neutrals and EGC conductors being mixed on both the ground and neutral bars of a panel where the bars are bonded. I have seen this a lot and I don't think that in and of itself that it is a problem until you want to install something ahead of it, like an ATS.
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That's what I meant. That makes running the sub panel ground and neutral conductors confusing to me.
 
Installer said:
That's what I meant. That makes running the sub panel ground and neutral conductors confusing to me.
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See post #5. If the bar has a connection to the neutral supply conductor via busbars and wires only, it's a neutral bar. If the connection is via the panel enclosure or other metal not used as a circuit conductor, it's a ground bar.

So in the service panel with the main bonding jumper, it is OK to land EGCs (ground wires) on the neutral bar. And in your photo you have only neutral bars. It is never OK to land neutrals on a ground bar.

Cheers, Wayne
 
wwhitney said:
But that is not what the picture shows. The picture show two (actually 4) bars that are insulated from the case, with a busbar between them that has a bonding screw to the case. Those are both neutral bars. There are no ground bars.

If you had one neutral bar insulated from the case, one ground bar mounted to the case, and a MBJ connecting the neutral bar to the case, then it would be a violation to land a neutral conductor on the ground bar. As the neutral current path would then be through the case. In the picture in the OP, the neutral current path is only through terminal bars and busbars, regardless of which terminal bar you land the neutral on.

Cheers, Wayne
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Of course, but an issue arises when an ATS (for example) is installed ahead of such a main panel; the N-G bond is now in the ATS and the jumper between the bars in the panel must be removed. The bars are no longer equivalent; EGCs must be connected to the one bonded to the enclosure and neutrals must be connected to the other.
 
wwhitney said:
For the panel shown in the OP, that would require adding ground bars, as there are none in the picture.
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Two possible solutions, in no particular order:

1. Install a pair of accessory grounding buses; the enclosure already has holes.

2. Cut the neutral strap, and use the side with the green screw as the EGC bus.
 
LarryFine said:
Two possible solutions, in no particular order:
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To be clear, solutions to the hypothetical that ggunn introduced; there is no problem with the photo in the OP. Those photos are all of the "main panel"; the only relevance of the term "subpanel" is that the OP is adding a feeder supplied from the main panel to a new subpanel elsewhere.

Cheers, Wayne
 
"You run a separate ground to the subpanel because you want the neutral current to return to the main panel via the neutral conductor." I would add the word 'ONLY' to that. or

'You run a separate ground to the subpanel because you want the neutral current to return to the main panel via the neutral conductor. and ONLY the neutral conductor.
 
OldBroadcastTech said:
"You run a separate ground to the subpanel because you want the neutral current to return to the main panel via the neutral conductor." I would add the word 'ONLY' to that. or

'You run a separate ground to the subpanel because you want the neutral current to return to the main panel via the neutral conductor. and ONLY the neutral conductor
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Good point. I guess I could have also said, “run a separate insulated neutral so the neutral current doesn’t return to the main panel via the grounding conductor.”
 
Installer said:
When I started to draw up the subpanel connections, I noticed that the Neutral bar on the Main Panel has Ground connections and the Ground bar has neutral connections.
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The panel that has the first disconnecting means will have a both N and G bonded and the bus will have both N and G branch circuits landed on them. The panel pictured does have all the bus es connected together so it is correct. This panel is likely to be a "Service Only" panel with the Neutral permanently bonded without a removable bond.
Issue I do see is the multiple Neutrals under single screw terminals and that is a violation. OP Picture show intent to use metallic conduits for connecting the 2 panels, technically if the metallic components are electrically continuous then all you would need is to bond the conduit at each end and wouldn't need to add the 4th wire in the conduit and then not bond (or isolate) the second panel Neutral from the enclosure and have a sperate ground bus electrically bonded to the enclosure.
 

1. Main Panel vs. Subpanel Bonding Rules​

  • In the main panel, the neutral (N) and ground (G) are bonded together. This is why you see neutral and ground wires on both bars in your main panel. The bonding ensures that any fault current has a direct path back to the source.
  • In a subpanel, neutral and ground must remain separate. This prevents unwanted ground currents (which can cause safety hazards and improper operation of circuit breakers).

2. Why Run Separate Neutral and Ground to the Subpanel?​

  • The neutral wire carries current under normal operation, while the ground wire is only for faults.
  • If you bond neutral and ground in the subpanel, return current could travel on both, turning ground wires into active conductors—which is unsafe.
  • Keeping them separate in a subpanel ensures that only the main panel handles the neutral-to-ground connection.

3. How to Wire the Subpanel Correctly​

  • Run 4 conductorsfrom the main panel to the subpanel:
    • Hot 1 (H1)
    • Hot 2 (H2)
    • Neutral (N)
    • Ground (G)
  • In the subpanel:
    • Keep neutral isolated (do not bond it to ground).
    • Connect the ground to a separate grounding bar, which is connected to the panel enclosure.
    • If the subpanel is in a detached structure, it may also require a grounding electrode (ground rod).
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