[akheilman]

Imagine a house with a properly installed main panel. I have to add a sub panel because the main panel is full. If all the ground bars were full would it be code compliant to add a double lug to the panel case and land both the ground and neutral of the sub panel to that lug? Would that cause the neutrals and grounds of the sub to be joined at both the double pig and the original main bonding jumper?

 

[FrunkSlammer]

The main is the only place you should bring neutral and ground together. So if I understand you correctly, you want to tie the neutral and ground of the sub panel feed in the main at the same point?

Sounds good to me, though some sparky's recommend keeping neutral and ground electrically the same point, but physically separate points for troubleshooting.. I don't care about that, though.

 

[Pharon]

The sub-panel should have separate neutral and ground buses that do not connect. The neutral and ground wires in the sub-panel feeder should go back separately to the main panel and get connected into those neutral and ground buses, respectively. See NEC 250.30(A).

 

[akheilman]

The sub-panel should have separate neutral and ground buses that do not connect. The neutral and ground wires in the sub-panel feeder should go back separately to the main panel and get connected into those neutral and ground buses, respectively. See NEC 250.30(A).

They would be separate at the sub but would be connected at the same lug that ties to the main panel case. This would connect ground to neutral twice inside the main panel.

 

[wendon]

Imagine a house with a properly installed main panel. I have to add a sub panel because the main panel is full. If all the ground bars were full would it be code compliant to add a double lug to the panel case and land both the ground and neutral of the sub panel to that lug? Would that cause the neutrals and grounds of the sub to be joined at both the double pig and the original main bonding jumper?

I'd never do it this way! What happens if the screw holding your double lug comes loose? You don't want to go there. Install a separate ground bar in the main panel. Bond it to the existing ground bar with a piece of #8. Move some of the existing grounding conductors from the original ground bar to the new one, freeing up space on the existing one. Install your neutral and your grounding conductors feeding the new sub-panel to the existing ground bar. Clear?

 

[Pharon]

They would be separate at the sub but would be connected at the same lug that ties to the main panel case. This would connect ground to neutral twice inside the main panel.

The neutral bus can be isolated by removing the bonding jumper between the two. Then the panel case will only be tied to the ground bus.

 

[akheilman]

I'd never do it this way! What happens if the screw holding your double lug comes loose? You don't want to go there. Install a separate ground bar in the main panel. Bond it to the existing ground bar with a piece of #8. Move some of the existing grounding conductors from the original ground bar to the new one, freeing up space on the existing one. Install your neutral and your grounding conductors feeding the new sub-panel to the existing ground bar. Clear?

Clear. Good point. Thank you, I'll do as you said. So technically it's not illegal then?

 

[FrunkSlammer]

Clear. Good point. Thank you, I'll do as you said. So technically it's not illegal then?

He's just saying losing a neutral can be disastrous to the connected loads.. if you're certain this will not happen, then there is no concern.

 

[wendon]

Clear. Good point. Thank you, I'll do as you said. So technically it's not illegal then?

I usually install separate ground bars in a main panel and land the grounding conductors on them. Even though the mounting screw bonds them to the existing ones through the panel frame, I still install jumpers. Just my practice. I had a local tell me that the mounting screw was no longer sufficient. Maybe someone has a code or maybe it's a local thing.

 

[wendon]

the sub-panel should have separate neutral and ground buses that do not connect. The neutral and ground wires in the sub-panel feeder should go back separately to the main panel and get connected into those neutral and ground buses, respectively. See nec 250.30(a).

250.32 (b) (1) is another one.

 

[Meadow]

Sounds like its time for a main panel change.