I know that this question has been asked and answered before however I have a possibly unique twist.

The old question: Does a sub-panel require that the ground and common wires be on separate bars?

The old answer: Yes.

So, looking at the 2 images below, the sub-panel in the second image would need to be corrected because as it is it is potentially dangerous. Correct?

  • Image 1 is the main panel where you can see common and ground separated. There is a 60 AMP breaker that feeds off to the sub-panel.
  • Image 2 is the sub-panel where the ground and common share the same bar.
    Question 1 To correct this, I would need to buy and mount another bar to the panel on the left side of the box directly to the metal without any plastic spacer to complete the ground and run a ground wire from the main panel ground to it that is the same gauge as the line/common wires coming from the panel? And then reroute all of the ground wires to it?

Now the twist...please scroll passed the 2 images for more

enter image description here enter image description here


It is unclear if the previous owner did this himself (he is now deceased) or if a licensed contractor actually did the work. My issue is I am now the owner and doing some renovating and need to clear this up. At first I simply thought that the original panel was too full to handle any more circuits hence the need for a sub-panel. But today I began run some new circuits and made the first of 2 revelations, the first up above. The second is that it is possible that number 1 above may be correct OR that number 2 could burn down my house, kill someone or both.

This brings me to image 3 below.

enter image description here

I first thought that the wires from the 60 AMP breaker in the main panel passed through this panel and into the sub-panel, which it actually does. However, it does so after the switch in this middle panel first.

The previous owner had this switch going to a giant extension cord that plugged into his gas powered generator I assume for power outages.

So now I am thinking that this panel was not merely for additional circuits, but rather to isolate certain circuits that he could power during an outage with his generator. That would explain the use of the red (stranded) wires from the three breakers in the sub-panel (on the right side) that go into the main panel and are wire nutted to other circuits. The latter I began separating prior to realizing this.

Facts The sub-panel breakers only work if the middle switch is flipped upwards ON. That is the side that is powered from the 60 AMP breaker in the main panel. In the OFF position pictured those circuits are off. Same as in the down ON position which of course plugs into the generator.

So more questions:

Question 2 Is question 1 above still valid? I would think either way It could not hurt to have separate bars and may be the only right thing to do.

Question 3 Is this actually a legit configuration. I am now living in Connecticut (US) and being from AZ and TX am not accustomed to major power outages so am unsure if this is new or not. It would be cool to have this as a backup someday but am not married to it and would just as soon remove it as it seems dangerous so your opinions are appreciated here.

There are probably more questions but will open this up for discussion first. I have more images of details and can provide clarification of the schematics if needed.

Thanks in advance!

A simplified drawing of how the three panels interact. I'll provide additional closeups upon request.

enter image description here

Main to switch detail.

enter image description here

Plug detail. enter image description here

  • Can we get those extra up-close pics? This is probably best analyzed for Code compliance as a unit...also, can you get us a pic of the generator inlet? Jul 15, 2016 at 22:15
  • @ThreePhaseEel - I just added a simplified drawing that shows exactly how the three boxes are tied together. If this is not helpful, I do have closeups of all three boxes from many angles. Thanks! Jul 16, 2016 at 0:17
  • The white wire from the main panel neutral bar to the subpanel in your diagram doesn't seem to exist in your photos. Jul 16, 2016 at 0:20
  • Also, is the run from the main to the transfer switch in a metal conduit nipple, or made some other way? Jul 16, 2016 at 0:20
  • 2
    yes -- a metal conduit works just fine as a ground wire Jul 16, 2016 at 0:56

2 Answers 2


This is related to what is known as separately derived systems and non separately derived systems, and it concerns avoiding unnecessary impedance on the grounding system that would adversely effect over current protection, i.e., breakers and fuses.

If the neutral is switched along with the phase conductors in the transfer switch, you have a separately derived system and you would NOT separate the grounds and neutrals in the generator only, which contains the main over current device "main breaker". You WOULD separate the grounds and neutrals in the sub-panel. Again, this is because the main over current device, "main breaker" is contained outside in the generator.

So, in your condition the generator is portable and thus does not fall under the permanently installed generator rules. But if it were, you would want to separate the grounds and neutrals at the generator and sub panel and be done with it.

To address your main question whether your current setup is safe. As mentioned above you ideally want the lowest impedance for ground fault protection. But by not separating the grounds and neutrals in the sub panel you are creating MORE impedance.

  • Thanks Kris. I do believe the gentleman that lived here had dialysis machines thus possibly the need for sustained power. Just a WAG there. Anyway, I have added a simplified wiring diagram to my post at the bottom. Although I believe I understand your explanation I do want to verify a couple things if I may. To be clear, the generator was not installed nor permanent, in fact it was moved with his belongings. A heavy gauge, three prong extension cord runs from the switch to where the generator sat. Not sure that matters but is of lesser concern. Continued below... Jul 16, 2016 at 0:31
  • My bigger concern looking at the drawing is that the sub panel does not appear to be grounded at all. The only ground wire runs straight to the extension cable which is not active. So the question is how best to ground it? I believe you may think that the ground was coming from the main. If so, can I simply run a ground from main into a newly added bar and move over the grounds in the sub thus separating the grounds and neutrals? And leaving the switch in the always ON (up position) the sub panel will always be powered via the main panel. Or is the best option removing the switch altogether? Jul 16, 2016 at 0:39
  • 1
    @Jared -- we need to know more about the setup to discern if the subpanel is grounded or not (remember, metal conduits are perfectly cromulent equipment grounding conductors) Jul 16, 2016 at 0:42
  • @Jared I've totally rewrote my answer which I feel better addresses your question.
    – Kris
    Jul 16, 2016 at 9:55

Forgive me for answering my own question. Credit goes to ThreePhaseEel and Kris along with many thanks!

I wanted to summarize all of the comments as this was a many fold question and some parts might get lost. In case this helps someone in the future.

My original system - is it safe and what needs to change was my original question. The original system (what I inherited) is a main breaker panel and a sub-panel separated by a 3-way switch that is fed by a generator. The purpose of the switch and sub-panel was meant to isolate certain circuits in the house (housed in the sub-panel) that can be powered via a gas powered generator connected to one leg of the 3-way switch and flipped in case of an outage.

Though not typical to your average home. This is a legitimate system, sort of. However, in my case, it was not executed correctly.

  • First, a system like this is meant to utilize a permanently installed generator that is properly grounded and has a separated neutral. This is because when switched to generator power, you are relying on the fault protection of the generator.

  • Next, while a panel can have a combined neutral and ground bar (why would you want to), it can only be the main panel. The sub-panel in my system has only 1 bus bar and both neutral and grounds are connected to it. See Kris' answer regarding impedance. The simple answer is add a second bus bar and connect it to the case grounding it. Then move the ground wires to it. Also need to make sure that the first bus bar is not grounded to the case physically or wired so that it can house only the neutral wires.

  • I was also concerned about the sub-panel not being properly grounded. The ground leg coming in to the sub-panel actually comes from the extension cord that feeds to generator leg of the switch (see wiring diagram image above). It led me to think that the sub-panel is not grounded unless the switch was in the generator position which it never is, and is plugged into a generator of which I have none. ThreePhaseEel pointed out that since these panels are indeed connected via metal conduit to the main panel directly which is properly grounded that these panels are directly grounded as well. However, if these panels were not attached to the main panel (say in another room, garage, shed, etc.) they would need their own independent grounding system.

Main and sub-panels defined - a main panel is the panel that has the utility feed (from the pole or underground and after the meter). A sub-panel is every other panel fed from the main panel regardless of location or distance.

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