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Old 05-24-2009, 11:56 PM   #1
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Generator SUB-SUB panel

My generator subpanel was installed with the help of an electrician years ago. He attached the both the white and green wires from the subpanel to the neutral bar in the load center. I remember asking him about this and him mentioning that neutral and ground both go to the same place anyway, and that it was only important that they be separate in the subpanel, which they are.

Well, I've learned more since then, and discovered that my load center has an isolated neutral bar, it is not tied to the ground bar. WHY? I wondered, then it dawned on me. There is no main breaker in my load center, the main breaker is actually beside the meter (50 feet away). Therefore, my load center is not the "main panel", it is technically a subpanel. Therefore my generator panel is a subpanel of a subpanel.

With this new knowledge, I assume it is not okay to connect the ground from the subpanel to the neutral bar in the load center, because doing so ties neutral/ground together, in a slightly indirect way. I have moved the green wire to the ground bar.

Does that sound like a correct fix? What bad things could have happened if I hadn't fixed this? With this configuration (Subpanel running off subpanel) what other issues/potential problems should I be aware of?

Last edited by Miranda7; 05-25-2009 at 01:29 AM.
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Old 05-25-2009, 02:14 AM   #2
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Generator SUB-SUB panel

Yes, you are correct. What bad things could have happened? The ground from the generator could have carried some neutral current, and depending on connections, possible energized the metallic frame of the sub panel or generator. Is that very likely? No, not really. In reality, it would have probably continued to operate fine for the rest of its life. But the chance still existed for parallel neutral paths.

How is the genny sub set up? Is it a transfer switch, or lockout or what? Just curious.
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Old 05-25-2009, 06:03 AM   #3
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Generator SUB-SUB panel

Except for how the ground wire and neutral wires are connected to its "parent", there are no other issues specifically related to "sub-subpanel" versus "subpanel".
The average homeowner who lost his house in the Oklahoma tornadoes should move for good and not rebuild. Too much complexity watchdogging the contractor. Too much a chance to be defrauded.
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Old 05-25-2009, 06:42 AM   #4
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Generator SUB-SUB panel

The reason you have a separate ground and neutral at subpanels is the same reason electrical outlets have a separate ground and neutral wire!

Let's take an outlet as an example. Say there was no separate ground wire, and that the ground was connected to neutral at the outlet.

Then let's say you have a microwave oven plugged into that outlet and the metal frame of that oven is connected to the ground prong of the outlet.

Then let's say a workman comes along and drills a hole into your wall to install something, and he accidentally drills through the neutral wire going to that outlet.

Now there is only a hot wire going to the microwave outlet...

You turn on the microwave and it does not work. Then you grab the metal cabinet of the microwave to move it to check the plug in the back and you get shocked! The hot connection is traveling through the "turned-on" microwave, then back out to the neutral connection, then to the ground connection at the outlet, then back up the ground wire to the metal cabinet! (Making the metal cabinet "hot".)

The same thing can happen with a subpanel basically. The only difference is the subpanel is further down the line. AND with something like this happening at a subpanel, EVERYTHING the subpanel feeds would have the problem of the metal cases being hot as opposed to the above example where just one outlet had the problem.

This separate ground/neutral wiring protects in certain "malfunction" situations, that being a broken (drilled through) wire. Or in the case of a "loose" connection. Actually these malfunction situations are not that rare.

As to the generator transfer switch, there are new OSHA rules that certain portable generators be equipped with a GFCI. In this case, a neutral connected to a ground can cause the generator GFCI to trip! (And this is a whole new set of problems!)
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Old 05-25-2009, 08:43 AM   #5
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Generator SUB-SUB panel

Wow, great information guys! Billy you have explained isolated ground better than anywhere I have seen it. You post should be a sticky!

The generator subpanel is a gentran, the type with the built in manual transfer switch/lockout. The generator is a portable generac, and the neutral/ground bonding strap has been removed from the generator. I also have a jumpered prong plug on hand to use to rebond the ground and neutral when the generator is used as standalone and not connected to the house. Sound right?

I have other questions relating to this generator panel under a thread "Arcfault grandfathered" and I would be VERY appreciative if you guys could take a look at that thread as well and give your opinions.

Last edited by Miranda7; 05-25-2009 at 08:49 AM.
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Old 05-25-2009, 10:26 AM   #6
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Generator SUB-SUB panel

Originally Posted by Billy_Bob View Post

Let's take an outlet as an example. Say there was no separate ground wire, and that the ground was connected to neutral at the outlet.
Then this is is non-compliant install from the start. Ground wires are and were never intended to carry current except fault current.
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