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Old 09-09-2011, 10:04 PM   #1
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Question about dual main panels


I've read through most of the related posts, but haven't seen this exact question before. I have two 200 amp panels in my house. They are right next to each other and each is connected directly to the meter. I even opened up the drywall to confirm there is a feeder coming through the wall into each of of 2 boxes. There is no wiring between the 2 panels.

In this setup, shouldn't each panel be considered a "main" and therefore have the neutral and ground bonded together? It's my understanding that neither of these would be considered a sub-panel. Only one of the boxes has a bonding screw installed, which doesn't seem right to me. I wanted to check to see if there was a reason why that would be.

Any help is greatly appreciated.

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Old 09-09-2011, 10:09 PM   #2
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Question about dual main panels


BOTH are considered main panels. You can actually have up to six "mains".

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Old 09-09-2011, 10:11 PM   #3
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Question about dual main panels


Does each panel have its own ground wire (GEC) going to an approved grounding electrode?
Why are you asking this question?
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Old 09-09-2011, 10:20 PM   #4
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Question about dual main panels


Yes, both panels have a ground wire going out to a ground rod.

I'm asking because I am in the process of wiring a subpanel in the garage, so I just opened up the boxes for the first time. I was making sure that both were actually main, and that one wasn't sub-ed off the other. That's when I noticed that only of of them had the bonding screw installed.
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Old 09-09-2011, 10:24 PM   #5
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Question about dual main panels


Do these panels have two ground/neutral bars that are linked together? If so, either bar could have the bonding screw.
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Old 09-09-2011, 10:32 PM   #6
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Question about dual main panels


No, I looked pretty carefully. The ground bar is on one side and the neutral bar is on the other. There is a metal plate at the bottom that runs from where the main neutral connects to the lug, connects to the neutral bar on one side, and runs out the other side toward the ground bar. There's a hole there that's clearly designed for a bonding screw. That's the only place where there could be a physical connection between the neutral and the actual ground bar. I suppose you could technically put a screw anywhere through that bar into the box and make a connection, but since there's clearly a hole there designed for a bonding screw I can't imagine doing it any other way. I'm sure there are no other screws in it. The one box has the bonding screw there, the other doesn't. I was going to put one in, but just wanted to make sure there wasn't a reason why I shouldn't. I've never worked on a setup with 2 mains before, so I figured it's always better to ask before you do something stupid.
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Old 09-09-2011, 10:46 PM   #7
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Question about dual main panels


Your GEC is connected to the neutral bar. The neutral bar is isolated from the panel case. The bonding screw is used to connect the case to the neutral bar. Is the ground bar screwed directly to the case?
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Old 09-09-2011, 11:04 PM   #8
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Question about dual main panels


The ground bar is screwed directly to the case already. The neutral bar is completely isolated from the case. The plate that connects to both the neutral bar and the incoming neutral lug doesn't touch the ground bar. However, the hole in it lines up with both a hole in the ground bar and a hole in the case itself. The bonding screw would connect all three.

I have one other question about actually running the wire for the sub-panel. Not sure if I should start a different thread, but since I'm here. I'm running a 100 amp circuit out to a detached garage. I'm using 2-2-2-4 aluminum wire. I will install a 100 amp breaker in the main box which has the lower load currently. I obviously connect the 2 hot wire to this breaker. There is an empty spot on the ground bar to connect the ground wire. However, I'm not sure how to best connect he neutral wire. There is no hole in the neutral bar large enough to fit my neutral wire. I could easily connect it to the main lug where the neutral comes in from the meter, but everything I've read says to never double tap a neutral connection. I'm going to have everything inspected by an electrician once I'm done to make sure it's all good, but I want to do it right in the first place. Is there some type of connector that will allow me to connect a larger #2 wire to the existing neutral bar, or do I need to do something else?
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Old 09-09-2011, 11:11 PM   #9
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Question about dual main panels


You panel should have a neutral lug adapter available. Square D has one called the LK70N.
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Old 09-09-2011, 11:19 PM   #10
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Question about dual main panels


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Originally Posted by drodge View Post
... I'm running a 100 amp circuit out to a detached garage. I'm using 2-2-2-4 aluminum wire. I will install a 100 amp breaker in the main box which has the lower load currently....
You can not use #2 Aluminum wire for a 100 Amp sub-feed. Either use a 90 Amp breaker, or #1 Aluminum wire, or #3 copper wire.
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Old 09-10-2011, 08:56 AM   #11
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Question about dual main panels


Jim - Thanks, it's a Square D panel and that's exactly what I need. I had no idea what to call it.

KBSparky- Thanks for the reply. The electrical people I've talked here said that no one uses copper here for feeding subpanels, which I guess is common elsewhere. They didn't even have copper that big when I went to look. The guy at Lowes told me use the 2-2-2-4, so I'll go back and see if the have #1 instead.
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Old 09-10-2011, 09:10 AM   #12
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Originally Posted by drodge View Post
KBSparky- Thanks for the reply. The electrical people I've talked here said that no one uses copper here for feeding subpanels, which I guess is common elsewhere. They didn't even have copper that big when I went to look. The guy at Lowes told me use the 2-2-2-4, so I'll go back and see if the have #1 instead.
Just for your understanding, #2 AL is allowed to provide 100 amp service to a dwelling but as for feeders it is limited to 90 amps.
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Old 09-10-2011, 09:17 AM   #13
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Question about dual main panels


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Originally Posted by drodge View Post
The guy at Lowes told me use the 2-2-2-4, so I'll go back and see if the have #1 instead.
Typical idiot at Lowes. They screw up this question all the time.
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Old 09-10-2011, 09:20 AM   #14
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Typical idiot at Lowes. They screw up this question all the time.
Don't forget the other place either. Why the store can give out "information" from unqualified people and get away with it I don't know.
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Old 09-10-2011, 09:24 AM   #15
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Question about dual main panels


I have to say off the record, MANY places still allow the use of #2SER for a 100A sub-panel. No one around here gives it a second thought.
#1SER is nonexistent around here, and 90A breakers are lame.

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