Main Panelboard Bonding jumper .

[Miguel c]

1. I am a little bit confused. Should there be a main bonding jumper between the metal frame of a first disconecting means or service panelboard and the grounding electrode conductor? The reason I asked is because I have seen some graphics in which there is not any bonding jumper between those.
2. Should there be a bonding jumper between the EGC and the metal frame of a subpanel?

 

[don_resqcapt19]

The equipment grounding conductor is always connected to the metal enclosure.
A main bonding jumper is only installed in the enclosure that contains the service equipment. The difference being is that at the service equipment the GEC, the EGCs, the panel enclosure, and the neutral are all connected together.
At panels on the load side of the service equipment the EGCs, the enclosure, and the GEC, if any, are connected together. The neutral is isolated.

 

[LarryFine]

There's always an MBJ, but it's not always a wire. It can be a bolt, or a bus, or even a bolted bus.

It's whatever interconnects the service neutral and the premises EGC system.

 

[K8MHZ]

There's always an MBJ, but it's not always a wire. It can be a bolt, or a bus, or even a bolted bus.

It's whatever interconnects the service neutral and the premises EGC system.

This has always been somewhat confusing to me. In a residential service, the green screw connects the neutral/grounding bar with the enclosure. The connection between the neutral and the EGC, since they are basically the same bus, will be there with or without the green enclosure screw. I don't see how that screw can be called a main bonding jumper.

 

[LarryFine]

This has always been somewhat confusing to me. In a residential service, the green screw connects the neutral/grounding bar with the enclosure. The connection between the neutral and the EGC, since they are basically the same bus, will be there with or without the green enclosure screw. I don't see how that screw can be called a main bonding jumper.

They're only the same bus in the service panel, if you intermix them.

I prefer wiring every panel as if it is or might become a sub-panel. In such a case, the screw is indeed the bonding jumper.

If you mix neutrals and grounds on the neutral bus, and ignore the EGC bus(es), that screw merely bonds the enclosure.

 

[K8MHZ]

They're only the same bus in the service panel, if you intermix them.

I prefer wiring every panel as if it is or might become a sub-panel. In such a case, the screw is indeed the bonding jumper.

If you mix neutrals and grounds on the neutral bus, and ignore the EGC bus(es), that screw merely bonds the enclosure.

So you purchase and add an EGC bar for service equipment? Then count on a few tiny screw threads to function as a main bonding jumper? I know that's OK per code, but still....

Edit to add: The green screw isn't really connecting the neutral to the EGC. It's bonding the enclosure which is now in series with the two. IMHO, this would not be permitted and the solution would be a short conductor bonding the two bars. Ditch the screw because the EGC bar is bonded to the enclosure already.

 

[romex jockey]

So any comment on multiple SDS's & MBJ's under one roof fit here?

~RJ~

 

[LarryFine]

So you purchase and add an EGC bar for service equipment? Then count on a few tiny screw threads to function as a main bonding jumper? I know that's OK per code, but still....

For EGCs, yes. The enclosure, just like conduit, functions fine for faults. Electrodes must still land on the neutral bus.

Edit to add: The green screw isn't really connecting the neutral to the EGC. It's bonding the enclosure which is now in series with the two. IMHO, this would not be permitted and the solution would be a short conductor bonding the two bars. Ditch the screw because the EGC bar is bonded to the enclosure already.

Yes, the EGC bus is bonded to the enclosure already. That's not what the green screw does, or is for. The screw bonds the enclosure, and whatever EGCs are connected to it, to the neutral bus, not the EGC bus.

Remember, without the screw, the neutral is isolated from EGCs, enclosures, conduits, etc. as you would have with any sub-panel.(there would be no GECs)

A conductor would be required only if neutrals were landed on the EGC bus, which could only be done in the service panel.

 

[LarryFine]

So any comment on multiple SDS's & MBJ's under one roof fit here?

Not in this discussion (so far).

 

[Miguel c]

The equipment grounding conductor is always connected to the metal enclosure.
A main bonding jumper is only installed in the enclosure that contains the service equipment. The difference being is that at the service equipment the GEC, the EGCs, the panel enclosure, and the neutral are all connected together.
At panels on the load side of the service equipment the EGCs, the enclosure, and the GEC, if any, are connected together. The neutral is isolated.

Thank you very much, now I undestand.