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This is the main panel, the green neutral bonding screw is there. How to differentiate the neutral and ground bars? In this case, does it matter which one I use as ground or neutral for the interlock kit installation?

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    Can you add a photo of the labeling on your panel? Not the listing of what the breakers do, but rather the label that talks about model number, screw torques, panel wiring, etc. – Harper - Reinstate Monica Aug 2 '20 at 18:46
  • Sorry, the wires blocking some of the information and I can’t move it too much. This is the best I can get, it’s QO load center has 40 breakers space, the interlock kit QOCGK2C fit perfectly. – 1997diyer Aug 2 '20 at 20:55
  • Alright, so you need bare minimum 40 neutral spots and 14 ground spots (assuming triple-tapping grounds, as is usually allowed). I see about 56, so that's about right. – Harper - Reinstate Monica Aug 2 '20 at 21:54
  • In this case, which one should I use as ground and neutral for the interlock kit installation? Thanks – 1997diyer Aug 2 '20 at 22:11
  • OK, edited my answer. That companion lug on the neutral main lug is fine for a generator NEUTRAL input. Don't use it for a ground. But the neutral bars are fine for grounds. – Harper - Reinstate Monica Aug 2 '20 at 22:40
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This is wired as a main panel (not a sub-panel), so they are effectively the same. Best practice is to wire grounds and neutrals separated in case this panel ever needs to become a sub-panel, but what you've got here now is a typical main panel where the neutrals and grounds are intermixed.

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  • Where are they connected, inside the house or outside in the transformer? I know how this is done in EU, but not in USA. – Mast Aug 3 '20 at 8:49
  • @Mast in the house. That's what the bonding screw in the main panel does. – Dan Is Fiddling By Firelight Aug 3 '20 at 10:32
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In a main panel with bond, there is no (functional) difference.

Many workers will still separate the functions, and "you tell" based on "what's in this bar? - White or Green/bare?" Also, Neutrals are one wire per hole, while grounds in most bars are allowed to be multiple wires per hole (check the label on the box for details and torques - and always use a torque driver.)

In a bonded main, mixing them is allowed, as they are "the same" due to the bond.

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You can use that lug for the neutral from the generator. I would not use it for ground. Go to a neutral or ground bar for that.

It appears all the bars in this panel are configured as neutral bars. There are ~56 neutral lugs, and 40 spaces, so barely enough neutrals. If you needed to run this panel as a sub, you would need accessory ground bars.


On a service panel, the metal chassis is grounded. It's important to be able to separate neutral and ground.

The key feature of a neutral bar is the insulation: it is insulated from the panel chassis. You only need to remove a ground screw or strap, and the bar is isolated from chassis.

Neutral bars have a heavy, high-current path between the bar and neutral lug, which is itself isolated from the chassis It is obvious that the neutral lug-to-bar connection is heavy, and designed to flow a lot of current all the time.


Ground bars are, by design, in direct contact with the panel chassis. This can't be removed; there'd be no way to isolate them even if you wanted to.

Ground bars may not have a dedicated electrical connection to neutral. They may rely on the case itself for their current flow to the other ground bars and any neutral-ground bonds.

In a main panel, there is nothing wrong with using neutral bars to attach grounds.

Do not put neutrals on ground bars. Their current paths are not designed to flow high current continuously.

If you see "an awful lot of neutrals", consider the worst-case for the panel, of every space in the breaker filled with a tandem/duplex/twin breaker driving a single circuit; thus you need twice as many neutral screws as you have spaces. If you have a gross excess of that number, then most likely the manufacturer intended some bars to be ground bars.

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  • If I following correctly. In my case, 1 2 3 4 all can use as ground. Which one should only use neutral? – 1997diyer Aug 2 '20 at 17:23
  • @1997diyer I edited for some more clarity. Please re-read... – Harper - Reinstate Monica Aug 2 '20 at 18:47
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"No, the neutral and ground should never be wired together. This is wrong, and potentially dangerous. When you plug in something in the outlet, the neutral will be live, as it closes the circuit. ... However, if there is something wrong and the neutral is disconnected, it will make the appliance dangerous."

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  • This doesn't speak to a situation within a panel – ThreePhaseEel Mar 24 at 3:51
  • Welcome to Home Improvement. Please take the tour to see how this Q&A site differs from general discussion boards. Also, since you have quotes around that text, it looks as though you copy/pasted from somewhere else. While that's acceptable to do, please include a link to the source. If it's not a direct quote, but your own words, please edit to remove the quote marks as they are misleading. – FreeMan Mar 24 at 15:05

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