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Electrical Code - USA Commercial or Residential 1999 / 2002 / 2005 versions - for UNITED STATES

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  #1   IP: 69.137.232.80
Old November 3rd, 2004, 05:33 PM
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Default Separating Neutral and Ground in a Subpanel

I'm in the process of installing a 40-amp subpanel in a small workshop on the back of my property and had a question regarding the neutral and ground connections feeding my subpanel. When I bring in the 8-3 into the subapanel......I'll connect the two hots to the hot lugs, which leaves the neutral and ground. On all the subpanels at my local home improvement store, it looks as if the neutral and ground bus bar are connected. Isn't the neutral and ground suppose to be separated? When I ask this question at the home improvement place......the so called electrical experts look perplexed! I'm comfortable with the wiring in a main pannel (residential), but I'm thrown off a bit on what to do with the neutral and ground coming into the subpanel. any thoughts???....Thanks.
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  #2   IP: 151.205.240.220
Old November 4th, 2004, 04:39 AM
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Don't let the fact that the clerk at the home center appeared perplexed. They are seldom the "experts" that they proport to be.

Yes, you are correct that the neutrals and the grounds need to be kept seperate in the subpanel. In some panels, that come factory equipped with two bars, you can seperate one bar from the other and use one for neutrals and one for grounds. The neutral bar must be insulated from the "can" of the panel, and the ground bar must be connected to the can. Still some panels contain only one bar, so you have to buy a "ground bar kit" (Such as Square D, 'QO'). Some panels come with two bars, but you still have to add a ground bar kit (such as Square D 'Homeline').

You can repost with the manufacturer and model of the panel that you propose to use, and an expert will respond with exactly how your panel is utilized as a subpanel.
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  #3   IP: 69.137.232.80
Old November 4th, 2004, 05:39 PM
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Question ground bar kit for subpanel

Even though it's only going to be a 40-amp subpanel, I purchased a 70-amp Square D, Homeline Indoor subpanel (it was available and inexpensive and the lugs looked like they would work just fine). So I assume I need a ground bar kit for the subpanel. Any thoughts on how to install the ground bar specifically would be great. Thanks again.
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Old November 5th, 2004, 05:20 AM
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Oh sure, that's a great panel for a subpanel (the breakers are certainly cheap enough). If you look at the back of the panel on the right and left sides (near the corners), you'll see 3 or 4 punched holes in a row. These are to accept the ground bar kit. You can use just about any square d ground bar kit in this panel. The part number starts with PK and ends with GTA with a number in between. I like to use two PK15GTA ground bar kits in the Homeline panels (one on each side). With a ground bar on each side, you will have a "neater" panel, since you won't have ground wires criss-crossing the panel to get to the ground bar. The "15" in the middle of the ground bar part number corresponds to the length of the ground bar. You can use one shorter or longer if you wish. I would highly encourage you to install one in each side though, just for neatness. They're certainly cheap enough.
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Old November 6th, 2004, 01:34 PM
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Default ground bar kit

I've got my subpanel in front of me now and I'm not sure if I'm looking at the right holes on the back of the panel. There's 1 hole in each corner for the attachment of the pannel to a surface and 6 knockouts if I were to run cable through the back of the subpanel as well (4 small ones....1 in each corner and 2 larger ones...1 at the top and 1 at the bottom of the panel for a total of 6. Other than that, there's only one additional hole in the back of the panel (if you were looking inside of it) that is 3/4 of the way up on the right side. And the whole location arond the screw hole is recessed into the panel a bit. Do I need to drill my own holes for the ground bar kit? Also, I don't need to run 4AWG copper from this subpanel to the ground....do I.............since the main panel is grounded correctly?

Just to be more specific about my subpanel:
70A, Main Lug, Indoor, 2 Spaces - 4 cirucits
Square D / Homeline

Thanks for the advice on using 2 ground bars. I think it will make the subpanel nearter and easier to work in if I ever need to work in it in the future.

Last edited by amp : November 6th, 2004 at 01:40 PM.
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Old November 6th, 2004, 03:45 PM
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Sorry, amp, I may have given some bad advice and confused you. I didn't realize that you were installing such a small subpanel, even though you did say that you were feeding it at 40 amps. Sorry. I take it you're using a HOM24L70F or HOM24L70S panel.

That subpanel will only accomodate one ground bar kit, to be installed in the factory swage punched hole. Normally there's a little ground symbol stamped into the steel at the location of this hole. The symbol looks like a little antenna. Don't worry if you don't see the symbol, sometimes it's not there. That panel will only take either a PK3GTA or a PK4GTA ground bar kit, which attaches with one screw.
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Old November 6th, 2004, 05:16 PM
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Default PK4GTA ground kit

md,
You're exactly right.....my 70-amp subpanel only accomodates 1 bar, thus the one small screw hole....I just figured this out...(sort of by accident as I was looking at all the ground bar kits at the store). I opted for the PK4GTA rather than the PK3GTA since it has an addtional hole in it for conductors to go. If I go any higher in length, the ground bar requires 2 screws to mount it, which means it needs two holes in the pannel (which mine doesn't have. My only other qustions are...

1. Do I need to attach some 4AWG copper to this ground bar kit and run it into the ground with a ground rod?....or am I ok since the main panel is grounded correctly?
2. Also, the green screw (that came with the subpanel) that bonds the other bar to the panel....I'm assuming I don't need that since this subpanel is a subpanel, rather than a main panel? Thanks for all the advice!
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  #8   IP: 151.205.241.225
Old November 6th, 2004, 06:00 PM
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I'm glad you got this ground bar situation figured out.

Quote:
Originally Posted by amp
1. Do I need to attach some 4AWG copper to this ground bar kit and run it into the ground with a ground rod?....or am I ok since the main panel is grounded correctly?
Yes, if this is a detached building, you need to drive at least a ground rod. You'll only need to run a #6 ground wire to the rod. Well, technically you could run a smaller ground wire to the rod for this small of a feeder, but #6 is the smallest gauge that the code will permit to run without some form of protection. If #4 is all that's available, use it if you want to. If this building happens to be served by a metal water line that is metal underground for a substantial length, then you could run the ground wire to this metal water line in leiu of driving a ground rod.
Quote:
Originally Posted by amp
2. Also, the green screw (that came with the subpanel) that bonds the other bar to the panel....I'm assuming I don't need that since this subpanel is a subpanel, rather than a main panel?
This is true, you don't need the green screw. These little 2-circuit boxes often get used as the temporary power breaker box on construction sites. In that case, the bonding screw would get used. In your case, no. If you're the sort of person that saves things, keep ahold of this green screw. They're hard to get ahold of seperately, and you or someone you know might need one some day. If you roll the screw's threads through your fingers, you'll notice that it feels "lumpy". Then, look directly in on the end of the screw. You'll notice that the screw is not round, it is triangular. This helps it get a good bite into the sheet metal.
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