Location of main versus sub panel & bonding of grounding & neutral conductors

When the same electrical services two different structures on the same property, should each structure have its own main electrical service panel?

With the multitude of different panel configurations, I often get confused about what is or is not a main or sub panel based on the way grounding and neutral conductors are bonded in each one.
Supposedly, when grounding conductors are bonded with neutral conductors, it’s a main panel.
But what if the electrical contractor made a mistake and bonded a rogue grounding or neutral conductor to the wrong bar? Then I have to know if it was intentionally done that way or a mistake.

Adding to the confusion is the fact that the local state electrical inspector has told me that the exterior service disconnect on a pedestal is not usually the main electrical service panel, even though the grounding and neutral conductors are bonded together in the same panel with the exterior service disconnect.

Check out these pictures of some panels that I inspected yesterday. I’m looking for help in determining which panels are mains versus subs in two different structures. One structure had a panel on an exterior wall and a sub panel on an interior wall.

The other structure had two panels on an interior wall.

Starting with the exterior service disconnect with the electric meter:

Then, it goes to the panel on the exterior wall of the closest structure:
The fat yellow conductor goes from the main panel of the first structure to the main panel in the second structure–connected to the neutral & grounding bus bar.

From the panel on the exterior wall, some panels on an interior wall of a different structure is fed.

Is this supposed to be a main panel? I’ve never seen a disconnect like this before. There’s obviously some solar hooked up to the system in this room.

Then, the panel that this one feeds just to the right of it. It has what appears to be a bonding strap connecting the grounding bus bar to the neutral bus bar routed behind the main bus bar. Is this supposed to be a main panel? If you don’t understand it any more than I do, is there something that you would say that I could to limit my liability with this?


Each “structure” should have its own grounding system (rods, foundation rebar ties, etc.). I say “structure” in quotes because for these purposes the pedestal is a structure. As you go to a different structure, the one feeding it essentially becomes the power pole and you start over again with grounds/neutrals tied together at first disconnect. All panels downstream of that disconnect in the same structure must have neutrals and grounds isolated.

The above are the general rules but, like everything, there are exceptions and some things that used to be done differently.

Edit: I just remembered a training document I put together a few years ago that addresses this. I think it might be slightly outdated as it seems all of the newer installs I see between buildings are 4-wire and they used to often be 3. There was some “if/then” about metallic connections between said buildings (typically water pipes) but those are now plastic so it’s no longer an issue. Honestly, after years of inspecting I still often question whether or not I’m calling this right. And it’s not just us HIs that struggle with this. I recently walked around a property with a journeyman electrician and he admitted it’s confusing and as inspectors we don’t always have all the info to know exactly what it going on.

Disneyland.pdf (352.7 KB)


That makes sense to me. Thank you, Matt.

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I just edited and added a training doc that I put together a few years ago that might help.

That Disneyland document was very helpful. That clears up a lot of my confusion about this for me.
Thank you, Matt!

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A separate structure has required a 4-wire feeder since the 2008 NEC. 3-wire feeders (with some exceptions that Matt mentioned) were permitted under code cycles prior to the 2008. A separate structure when fed by a feeder requires a connection to a GES (grounding electrode system) with a GEC (grounding electrode conductor) to the EGC bus in the sub-panel. This GES may be as simple as two ground rods.

A separate structure also requires a disconnecting means which is often a main CB in the panel but it could also be a disconnect switch. When a separate structure is fed by a single circuit or a MWBC it does not require a GES.

I would avoid using the term main panel. The panel that contains the service disconnecting means is the service or if you so choose the service panel. All other panels downstream of the service are “sub-panels”. I put that in quotes because that term is undefined by the NEC but just about everyone knows what it means.


Isn’t this exactly the opposite of what @mfellman told me in the string that:

I usually use the term “main electrical service panel.” Is this term too vague or inaccurate?

I’ve seen plenty of sub panels that have a main disconnect breaker, so that’s a really confusing statement for me. Why would a panel enclosure with a main disconnect switch inside of it have any bearing on whether or not the panel is a service or sub panel?

Again, this statement completely contradicts what @mfellman just told me that basically says if a panel is the first one downstream of the first service service panel and on a separate structure, it can also be a service panel. This is what he said:

Are you saying that what @mfellman said above was inaccurate?

That is why the word “Main” should never be used. It confuses a lot of people.

Every electrical service has One Service Disconnect (in your case at the meter). All other panels Downstream are remote distribution panels. The " Main" breaker that you see at the remote distribution (sub) panels is Only a disconnect switch.


For this one, I believe what Robert is saying is that if the separate structure only has one circuit, it does not need to have a GES. In other words, you have a breaker labeled “detached garage” in the distribution panel in the house. The wire from that breaker goes to the garage and serves 2 outlets and a light in the garage. In this case, no GES is needed for the garage because it has only one circuit.

And @rmeier2 , correct me if I am wrong, but in the scenario above, we don’t even need a disconnect means in the garage do we?

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That is correct in the 1st paragraph, a separate structure fed with only one circuit or a MWBC does not require a grounding electrode system. For the purpose of this specific code section a MWBC is considered to be one circuit.

Regarding the disconnecting means for a separate structure it is still required even for a single circuit like one that provides power for a light and receptacle in a detached garage. It can be a toggle switch.


IMO that is fine since it contains the word service. IMO any other panel that isn’t the service panel can be called a sub-panel because it is widely known as a sub-panel.

The panel that contains the service disconnect (can be a main CB) is the place where the MBJ (main bonding jumper) is installed. The MBJ is commonly the green screw that bonds the neutral bus to the enclosure.

Any panel that is downstream of the panel with the service disconnect cannot be a service panel even if it’s in a separate structure because only the first upstream panel will have the MBJ installed. Back when it was permissible to have a 3-wire feeder to a separate structure (pre-2008 NEC) even if you bonded the neutral at the remote panel within the separate structure it still is not a service panel because it is fed by a feeder not service entrance conductors.

I know that this is confusing because there are many different terms to understand. That is one reason why using the proper terminology is important.

I left out the exception about a single circuit… and likely several others :slight_smile:

So, yes, what I said is technically incorrect. I should have said any panel should have it’s own grounding rather than any structure.

Any of your older guys that used to hang out on the Inspectionnews.com forum might remember Jerry Peck. He would go absolutely crazy if anyone ever used the terms “sub panel” or “main panel”. They are either “service equipment” or “non-service equipment” (he is technically correct but all his blowhard BS got in the way of an otherwise good lesson). I never understood his hype since it really boils down to EVERY panel you look at is setup in one of two ways. You can call them apple and orange if you want. One is the first stop and has neutrals/grounds bonded, the other isn’t/doesn’t.

And finally - I’m relieved that Robert Meier looked over my posts and hasn’t crucified me :slight_smile: He’s obviously more versed on this stuff than me and just about anyone else I’ve seen hanging around here. Point being - listen to him!

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Doesn’t this kind of throw the whole “Disneyland” explanation out the window if there’s only one main panel with a main bonding jumper installed? Remember, this is what the Disneyland document said:

Once you leave the “Disneyland” of a given structure and move to a SEPARATE structure you
start all over again. You can have a 3 wire feed from a house to this detached outbuilding. At this point
the main house essentially becomes the power company for the outbuilding and there is another
“Disneyland” in the detached structure.

If the detached structure was only fed by a 3 wire feed the panel was again bonded like a service. There were certain conditions that needed to be met to allow the 3 wire. This was changed in the 2008 NEC. Now detached structures require a 4 wire feed. An existing 3 wire feed is allowed to remain in service.

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Not sure I’m following - Basically, every structure starts over from scratch as though the feed is the power company - or it could be a feed from another building. Prior to 2008 (thank you to those clarifying the date) a house could act as the power company and send a 3-wire feed to an outbuilding. 2008 forward - house to outbuilding must be 4-wire. This doesn’t change the fact that every panel is one of two types: Service Equipment (aka “main”) = grounds/neutrals bonded, NOT service equipment (aka “sub panel”) = grounds neutrals isolated.

I would add that there is a third type, the pre-2008 panel in a separate structure with a 3-wire feeder and a bonded neutral. Even though the neutral is bonded it is not service equipment.

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How do you know what the difference is between a feeder and a service entrance conductor in the field?

When there’s a green MBJ installed on a panel that’s supposed to be a sub, what would you say about that in the report?

Since I’ve gotten conflicting information from most comments on this thread, and from the state electrical inspector, maybe I need to find some other training. Who offers training to electrical inspectors in the field? I need some in-person training on grounding and bonding, and I’ve already taken most if not all of InterNACHI’s electrical classes.

The service conductors end at the service disconnect. In a dwelling this is typically the panel or disconnect that is fed from the meter. After that the conductors that are run to another panel, be it in the same structure or a separate structure, would be feeder conductors.

If the sub-panel is in a separate structure, is installed under pre-2008 NEC, and has a 3-wire feeder then the MBJ (green screw) is required to be installed. Without the green screw the panel would be ungrounded.


That’s good to have a more precise terminology to use for those feeders. Thank you for sharing that. I will use that more accurate wording.

With that said I would think that sub panel with a 4-wire feeder should not have a green screw on the neutral bus bar.