Bonding before main disconnect

[Doc13067]

With regard to the GEC being bonded to the neutral at one of 3 locations, in residential I always make the bond at the first disconnect (in my case that’s almost always an indoor main breaker load center, although sometimes it’s an outside disco or ATS). If the GEC is ran to the meter socket or the service drop, for that matter, what happens afterwards, particularly at the main disconnect? I have a situation that I believe falls under 250.24(A)(3) because there are two meter sockets connected by RMC and a ground rod under them with an aluminum GEC that runs from the rod (I know, 250.64(A)) to the first meter socket and is under the same lug as the line side neutral. From there a 3-wire SEU cable goes in to the main disconnect. There is a separate GEC going from the main disconnect to a water pipe but I never understood if the “main disconnect” should be bonded or isolated when there is a GEC landed before it. I can’t seem to find the answer in the code book. Could someone help me understand this and advise on what to do with the two separate GECs? This was done in 1978.

 

[jaggedben]

I find your description of the installation confusing (are there two service disconnects?) but here are the general principles.

You always have an Main Bonding Jumper in each service disconnect. No matter the GEC location. That is bonding.

You can have the GEC at the service disconnect or anywhere upstream of the first disconnect. The NEC doesn't require the GEC connection to be in the same place as the MBJ.

If you have multiple service disconnects you can have multiple GECs or GEC taps or run a single GEC to a common point upstream of all disconnects. See 250.64(D).

It sounds like your aluminum GEC might not be compliant with the latest code although I can't speak to whether it was compliant in 1978.

 

[augie47]

My read is you have to Grounding Electrode Conductors from two points one from meter, one from service panel) to two different electrodes.
I don't see that as a violation. GEC can connect anywhere up to and including the service and there is no requirement they must all terminate at one point.
(The AL GEC to the rod pn the other hand)

 

[TwoBlocked]

...

You always have an Main Bonding Jumper in each service disconnect. No matter the GEC location. That is bonding.

...

Recently came across an installation that has the neutral bolted to the backplane in the metal meter box (MBJ), metal conduit going to the metal main service disconnect, and the ground connection (GEC) going to the back plane of the main disconnect. I didn't like the looks of it and may have the opportunity to change it.

Installing services is not my main line of work. Can you point out the NEC article requiring an MBJ in every service disconnect?

 

[augie47]

. Can you point out the NEC article requiring an MBJ in every service disconnect?

250.24 and 250.28

 

[Doc13067]

If the neutral is bonded to the GEC in the meter socket or at the service drop and you have a 3 wire SEU cable going from the service drop to the meter to the first disconnect, what happens at the first disconnect since the bond has already occurred?

 

[Doc13067]

Recently came across an installation that has the neutral bolted to the backplane in the metal meter box (MBJ), metal conduit going to the metal main service disconnect, and the ground connection (GEC) going to the back plane of the main disconnect. I didn't like the looks of it and may have the opportunity to change it.

Installing services is not my main line of work. Can you point out the NEC article requiring an MBJ in every service disconnect?

And my question with this is should the neutral now be isolated in your main disconnect.

 

[TwoBlocked]

... Can you point out the NEC article requiring an MBJ in every service disconnect?

250.24 and 250.28

Thanks, another question if you can help me. If there an article requiring a MBJ in the meter enclosure?

 

[TwoBlocked]

And my question with this is should the neutral now be isolated in your main disconnect.

250.24 and 250.28

Nope.

 

[Doc13067]

Nope.

If it’s not isolated you’re going to put objectionable current on the GEC or SSBJ. And 250.24(A)(5) seems to say that a neutral should not be connected to metal enclosures and conduits etc. to prevent objectionable current. If you bond in the meter isn’t the disconnect going to be treated as the load side of the service equipment? It is looking to me like the main disco or indoor panel (whatever the first disconnect after the meter is) neutral must be isolated and a SSBJ should run between the point of bonding and the ground bus/enclosure of that main disco or panel.

 

[infinity]

If you bond in the meter isn’t the disconnect going to be treated as the load side of the service equipment?

No the meter is not the service equipment. Every metal part ahead of and including the service disconnect gets connected directly to the neutral.

 

[Doc13067]

So then it is acceptable to have the portion of the grounding electrode system that connects the bonded main panel to the bonded meter socket in this example sharing objectionable current?

 

[jaggedben]

If the neutral is bonded to the GEC in the meter socket or at the service drop and you have a 3 wire SEU cable going from the service drop to the meter to the first disconnect, what happens at the first disconnect since the bond has already occurred?

"The bond" has not occured. You still always need an MBJ in the disconnect. The MBJ connects all EGCs on the load side of the disconnect. Bonding the neutral to the meter can does not do that. With SEU you have parallel path between the meter and the disconnect.

Grounding and bonding are not the same thing. Again, the NEC allows you to do them in different places. Stop thinking of a GEC as performing bonding. The MBJ performs the bonding, always.

 

[jaggedben]

If it’s not isolated you’re going to put objectionable current on the GEC ...

There is no such thing as objectionable current on a GEC. If you choose to ground a system at multiple points, as the NEC effectively requires (because it requires us to ground services that are already grounded on the utility side), then some earth current will occur, however large or minute. This cannot be objectionable according the NEC if the NEC requires.

 

[jaggedben]

So then it is acceptable to have the portion of the grounding electrode system that connects the bonded main panel to the bonded meter socket in this example sharing objectionable current?

What portion of the grounding electrode system are you talking about? You haven't described such a connection.

 

[roger]

So then it is acceptable to have the portion of the grounding electrode system that connects the bonded main panel to the bonded meter socket in this example sharing objectionable current?

Is this what you are thinking? It's shown as the EGC in the illustration and no it's not acceptable. Take the EGC out and all is fine. The neutral from the meter will be the fault clearing path through the Main Bonding Jumper (screw in the illustration), the GEC is fine where it's shown.

 

[LarryFine]

If the neutral is bonded to the GEC in the meter socket or at the service drop and you have a 3 wire SEU cable going from the service drop to the meter to the first disconnect, what happens at the first disconnect since the bond has already occurred?

The neutral and the grounding electrode were bonded in the meter.

The premises EGC system starts at the disconnect, which is also bonded.

There are still only three conductors, no EGC,thus no parallel current pathway.

 

[Doc13067]

The neutral and the grounding electrode were bonded in the meter.

The premises EGC system starts at the disconnect, which is also bonded.

There are still only three conductors, no EGC,thus no parallel current pathway.

Thanks Larry. So the grounding electrode system is terminated in the meter. Then 3 wires leave the meter and go to the main panel. No GEC goes to the main panel. But the main panel has the neutral bonded to the enclosure (bonding screw down). So in this case the service neutral connects the panel to the grounding electrode system. Am I understanding that correctly? This makes a lot more sense.

 

[LarryFine]

Am I understanding that correctly?

Mostly, yes. Electrodes may connect to the service neutral wherever convenient, including the main panel, and they all need not be connected to it in the same place.

You're lucky; we're not allowed to land ours in the meter, which is a shame, as it's the ideal location to land the GEC to driven rods.

 

[Doc13067]

For sure! And lots of meters come with ground terminals and the bonding bridge is best located under the meter. However, I don’t know if we’re still allowed to do this. I’m just working on a system that was placed in 1978 and I believe it’s this way because 2 services meet in one of the meter enclosures.