Need help with Concentric rings and bonding

Little confused with coencentric knockouts and when your required to use a bonding bushing or grounding wedge. The service panel in this picture has non metallic conduit between panel and meter. The panel has concentric rings at the line side of the panel. Correct me if im wrong but since non metallic raceway was provided you dont have to use a bonding or grounding wedge, Correct? Any one have any good reference on this?

Thanks in advance



Non metallic raceway used between meter and service panel because the meter was grounded?

I have no ides what this means. Can you re-word the question?

Yes, since the raceway between the enclosures is NM there is no concentric KO issues. The raceway has nothing to do with grounding/bonding so the KO’s are of no consequence.

In my area meter pans do NOT get “grounded” by anything but the service neutral. We used to have to hit the meter pan with a GEC but this was dropped years ago. Now all GECs go to the main panel/disconnect.

You cannot “bond” non-metallic parts, so there will be no reference to support this.


In this picture the connection between panels is PVC, the "Grounded" conductor would apply the connections required in this setup.

When assured bonding is required for example on Ess. and Cons. KO's it would be required to use the methods you have stated....either a bonding wedge or ring for other cases a bonding busing is used.

Here…this might help explain it better

**(B) Method of Bonding at the Service. **Electrical continuity
at service equipment, service raceways, and service
conductor enclosures shall be ensured by one of the following

(1) Bonding equipment to the grounded service conductor
in a manner provided in 250.8
(2) Connections utilizing threaded couplings or threaded
bosses on enclosures where made up wrenchtight
(3) Threadless couplings and connectors where made up
tight for metal raceways and metal-clad cables
(4) Other approved devices, such as bonding-type locknuts
and bushings

Bonding jumpers meeting the other requirements of this
article shall be used around concentric or eccentric knockouts
that are punched or otherwise formed so as to impair
the electrical connection to ground. Standard locknuts or
bushings shall not be the sole means for the bonding required
by this section.

But without going into too much detail in the example you show here the panel to the left is backfed, it should have it's own support ( unless it is bolted type and I dont think it is ) holding it addition to it's current support methods.

I am curious however…how come they did not simply terminate on the MLO terminals…it is clear that if this is a service it is under the 6 throw allowance…

anyway…hope it’s helpful

Sorry Paul, Im not following?

Sorry Petey, I worded my question poorly.

The neutral is usually bonded in the meter base, I assume that is what Ian is talking about. Depending on how your AHJ feels about parallel paths and how they read 250.142(A)(1) they may not want to see a parallel path from the meter can to the service disconnect can.
Some say it is no sweat but there are still some crusty old guys who say “parallel neutral” and don’t want to see any path but the white wire. (plastic raceways or SE cable).
I tend to agree with those who say on the line side of the service disconnect/MBJ there is no problem with those parallel paths particularly if it is a massive total path. (like industrial switchgear with multiple 4" RMC risers, all using bonding bushings and jumpers the size of your finger)

lol…I lost you did I James…lol…

Ok…Basically I don’t see a requirement for a Bonding Wedge or Ring in your photo since the connection between the meter enclosure and the service panel is non-metalic in nature ( ie: PVC )…using PVC like they did on this image is saving the issues Greg is refering to…

The " Grounded " conductor is serving it’s proper function in this example you have posted.

The example I was saying about the KO’s was to explain that if assured bonding is required lets say at the service equipment as the NEC speaks about in 250.92(B)(4)

Note that method (4) in 250.92(B) requires other similar devices, such as listed bonding-type locknuts or bushings. Standard locknuts or sealing locknuts are not acceptable as the ``sole means’’ for bonding on the line side of service equipment.
Grounding and bonding bushings for use with rigid or intermediate metal conduit are provided with means (usually one or more set screws that make positive contact with the conduit) for reliably bonding the bushing and the conduit on which it is threaded to the metal equipment enclosure or box.

Grounding bushings used with rigid or intermediate metal conduit or with tubing (EMT) fittings, such as those shown in Exhibits 250.35 and 250.36, have provisions for connecting a bonding jumper or have means provided by the manufacturer for use in mounting a wire connector. This type of bushing may also have means (usually one or more set screws) to reliably bond the bushing to the conduit.

Light bulb just came on, its dim but does come on some time Paul. I see what you mean about back fed. No Idea why they would do that. Seams like more work to me.

yeah…sorry…I kinda jumped onto another topic on ya…but it’s all good because it is helping you learn and thats the only goal here.

But without going into too much detail in the example you show here the panel to the left is backfed, it should have it’s own support ( unless it is bolted type and I dont think it is ) holding it on…in addition to it’s current support methods.

Paul was this meant with the set up that I show? What do you mean by holding it on.

Man the more I learn about electrical the more I realize I dont know anything. Make it stop.

lol…meaning it needs to be held on when backfed by something other than just clicking it in…in other words if it is backfed it must meet this code requirement.

**(F) Back-Fed Devices. **Plug-in-type overcurrent protection
devices or plug-in type-main lug assemblies that are
backfed and used to terminate field-installed ungrounded
supply conductors shall be secured in place by an additional
fastener that requires other than a pull to release the
device from the mounting means on the panel.

Paul, there is a white, possibly clip on that 125 amp breaker. It appears to be bolted to the enclosure and looks like it lays over the top of the breaker.

That white clip is the breaker retention device.

most excellent…could not see it in the picture but then again I am getting older…:wink:

still do not know why they went through all that trouble…in regards to backfed of the breaker to begin with…but alas what is done is done.

Anyone want to comment on the ground bar with nothing on it, the grounds on the isolated neutral, and the neutral bar isolated(no green/bonding screw)?

Seems like the serious issue here(or I’m looking at the photo wrong). :smiley:


I think I see a “Z” bar strap in the back of this panel shown which is doing the bonding at the main service equipment, This is the first disconnection location and the “Grounded” and " Ground " terminations should share the same buss bar…it is the panel INSIDE I worry about…because that one we can’t see…:wink:

Now dont get me wrong thomas…maybe I am looking at the wrong picture or have not had ALL my coffee this morning…entirly possible…as I am going for my 3rd cup right now…( working on pricing a plan so I am bored )

Paul , your are correct. The panel shown is the service equipment panel not the distributiion panel. The distribution appeared to wired properly.