More than one wire to a hole/set-screw on neutral bus bar?

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Robert Green wrote:

Bobby That's fine as long as the label indicates that the terminals will except more then one wire. If the label does not list multiple wire combinations under one screw then you are gambling but you are not risking much. The supplemental buss bar is the way to go if you want to do it right. -- Tom Horne
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Robert Green wrote:

Bobby That last idea is a problem right from the start. The reason that the electric code specifically forbids connecting two neutral conductors under one terminal is that the two circuits will be loaded and unloaded in a random way during normal use. Each of the conductors will then expand and contract at different times causing the connection to the more lightly loaded of the two wires to be looser than the connector is designed to be and inducing heating in that connection beyond it's design limits. That leads to connection creep which gradually makes the connection less and less firm. Eventually arcing occurs and the neutral goes open leaving a circuit that appears to be dead energized from the breaker all the way back to the open neutral connection inside the panel. As one example of the danger to persons the screw shell of Edison based screw in light bulbs would be energized at 120 volts to ground. Someone thinks the bulb is burned out and tries to change it. If their finger comes in contact with the screw shell while they are unscrewing the bulb they get a shock. Even if there is no path to ground through their body their startle reaction alone could throw them off of a ladder or cause them to fall. If they are also in contact with some grounded conductive surface such as the metal surface of an installed lighting fixture they could receive a fatal shock. SquareD makes an isolated ground buss bar that is designed to be added to a panel were isolated grounds need to pass through a panel without being connected to other Equipment Grounding Conductors (EGC) in that panel. Installing one of those buss bars is a perfectly safe way to add additional neutral terminations to any panel No matter what the panel is being used for. It would be a technical violation of the panels listing and the listing of the isolated grounding buss bar but it would not in fact be unsafe as long as there is plenty of room in the existing cabinet to install the buss bar and the room to bend the additional conductors to each terminal. The additional buss bar would be connected to the the original buss bar by a copper conductor at least as large as the main bonding jumper called for in 250.28 Main Bonding Jumper. (D) Size.
250.28 Main Bonding Jumper. For a grounded system, an unspliced main bonding jumper shall be used to connect the equipment grounding conductor(s) and the service-disconnect enclosure to the grounded conductor of the system within the enclosure for each service disconnect. (D) Size. The main bonding jumper shall not be smaller than the sizes shown in Table 250.66 for grounding electrode conductors.
If your panel is two hundred amps or smaller then that wire need be no larger than number four copper. IF AND ONLY IF YOUR PANEL IS ALSO THE SERVICE DISCONNECTING MEANS FOR YOUR HOME you could just install a supplemental Grounding buss as others have already suggested. Since the Equipment Grounding Conductors and the Grounded Current Carrying Conductors; by which read neutrals; are bonded to each other and to the cabinet you can use the supplemental EGC buss bar in the same way you use the neutral buss bar. In order to avoid having neutral current traveling on the bonding connections through the steel of the panel's cabinet you just add a main bonding jumper between the two buss bars so that current from any neutrals you terminate on the extra buss bar will have a low impedance pathway back to the utility neutral and thence back to it's source in the utilities transformer secondary winding. -- Tom Horne
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That's in line with what I had read, although it thought it was really only a problem for CU and AL mixes. As I now understand it, the critical difference between allowing multiple wires to a set-screw hole for grounds and but only one wire to the same hole for neutrals is that the latter is designed to carry current in normal operation but the grounds are not. An open neutral is a far more drastic fault than an open ground, correct?
<stuff snipped>

Yes, I learned that after so many people told me that there should be wire connection info in the panel. Since the panel's in an awkward place, I couldn't see one inside edge of the box without a lot of contortions. I used a tilt-head camera to photograph that part an inside was a label that said:
"When grounding bar kit is req'd, use kit PK 9 GTA for QO 12MW and PK 12 GTA for QO 16MW and QO 20MW Suitable for #14 to 4 CU, #12 to 4 AL, TWO #14 or 12 CU or TWO # 14 or TWP #12 or 10 AL. This box used with interiors QON 12M, 16M and 20M May be used with auxilliary gutter Cat # QOAG17m 26 or 34."
What's an Auxilliary Gutter? When it says TWO # 14 or 12 CU what exactly is it referring to?

Size.
Thanks Tom. I searchedEbay for the correct grounding kit for that panel but nothing showed up. I guess it's too old for even the liquidators to have one. I just counted up the grounds going to the neutral bus bar and if I moved them to a supplemental bus bar, I can have all the neutrals from the new outlets mounted one to a set screw on the original factory installed neutral buss bars. Not quite sure what gauge wire I should connect to between the ground bus and the neutral bus. In doing some futher searching I found this:
http://www.selfhelpforums.com/archive/index.php/t-2278.html
Which had an interesting exchange:
<MD, when you use two or more ground bars like this do you normally wire them together with a "bond" wire, or is the panel mounting enough? >
<<For commercial work, particularly in 277/480 panels, yes I do. In a dwelling, I do not. If you said that you wanted to, there would be nothing wrong with that. I have just never felt the need to do so in a residential panel where the available fault current comparatively not that great.>>
That would lead me to believe some sparkies do simply ground the bus bars through the panel. I am afraid that I may not have enough neutral setscrew hole openings if I use a jumper between the ground and the neutral bus bars and that I may still have to mount a neutral to the ground bar because I'd be short by one neutral. I'm not sure which is worse: the neutral and ground being connected by the steel case or a lone neutral being connected to the supplemental grounding bar.
Who ever thought adding a couple of extra outlets could be so much fun? )-:
-- Bobby G.
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PK9GTA and PK12GTA I believe are the grounding bar kits for Square D's current line of panels, so they should be readily available at your local electrical supply.

That the grounding bar (unlike the neutral bar) is listed for two conductors of that size per hole.

I would say the latter is worse, as it causes some neutral current to pass through the enclosure case all the time, while the former simply makes the case part of the EGC system.
Cheers, Wayne
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wrote:

GTA
I was able to adapt the Cutler Hammer bar by drilling out one of the holes. The CH bar's mounting holes were much closer together than the Square D's, but they were on the same centers so I lost one wire set screw hole by converting it to a mounting hole. The newest problem is that no matter which side of the box I mount it on, some of the ground wires just won't reach because they were cut to reach the neutral bar that was very close to the top of the box where the wires enter. The solution, I suppose is to mount a bar on each side of the box. I think I can get them all to reach then. I may also be able to pull new wire to replace the short one.

OK. That makes sense since they are discussing the grounding kit options on that label as well.

Yes, I see. I also have a new option. We no longer use our central A/C so I may end up disconnecting those wires from the panel to give me some more space. I hate to do it, but I am adding the 220VAC outlet primarily to drive a coupler/repeater for my X-10 lighting control which I will remove before we move. That would mean disconnecting the A/C wires, taping and capping the ends and leaving them inside the box until it was time to reconnect them. That's probably a code violation, too, but it's one I can live with.
Thanks for your help, Wayne.
-- Bobby G.
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Robert Green wrote:

Bobby If you bond the two together with a copper conductor you can use either one for the neutral conductors because electrically speaking there would be no difference between them. If you only need the extra buss bar to move Equipment Grounding Conductors (EGC) to then don't bother with the bonding conductor. In that second case the steel of the cabinet would only have to briefly carry fault current and that job it can do very adequately. -- Tom Horne
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<stuff snipped>

Understood. I think I finally have this under control and understand the reasons for the various rules and methodologies. Now the problem is dealing with the ground wires that are too short to reach from the old top mounted neutral bus to the new side mounting supplemental ground bus bar.
-- Bobby G.
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On Tue, 18 Dec 2007 21:50:56 -0500, "Robert Green"

Don't get too crazy about this, just splice on another wire the same size with a wirenut
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besides
The panel label should have the information that you need. Usually you can double or triple the ground wires together. The neutral wires must be by themselves. As others have suggested it is possible to add a ground bar to the panel.
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It's a Square D QOC-20MW (on the cover label) but a QO8W-20M100-5 on the panel label. There are three diagrams on the label and the one that appears to apply shows three levels of neutral bus bars with arrows pointing to the center of the center bar. One arrow says "Box bonding when required" and points to the very center of the bar at a O in between two X's. The other says "Ground when required" and points to the innermost left setscrew on the center bus.
v [ O O O O X o X O O O O ] ^
(The O's are set screws There's also an abbreviation S/N next to a circle that's drawn inside the lines of the third bus bar. On the other two drawings where there are only two bus bars, the circle is outside the bus bars.)
Not anything written on it that would seem to shed light on the "more than one to a hole" issue.
The box label has 4-81 in the lower left corner and the box's forged inspection label is dated 6/82 so I assume this box is 25+ years old.
-- Bobby G.
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With some Square D panels the covers are sold separately. Hence the model number difference. There may be one small sentence somewhere inside the PANEL label that states the wire sizes and number of wires for the neutral/ground bar. Look for "Wire range 4 -14" or something to that effect.
You should be fine with at least doubling up the grounds. If you need more room add another ground bar.
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<<Somewhat repeating gfretwell - ground wires can be doubled up but only if the label indicates that is permitted.>>
I will check the label shortly and report back. I think it's a Square-D circa 1981.
<<Neutrals may NOT be doubled up - NEC 408.41>>
Well, at least I can be thankful I'm not completely senile. I do recall reading one to a hole *somewhere* during my life. IIRC, it was because the setscrew wouldn't hold two wires as securely as one, but it seems there are other considerations as well.
<<In a service panel you can add a ground bar which the label indicates is acceptable and move ground wires to it. In a subpanel that doesn't help.>>
It's a main panel in a very small house. More details to follow for the experts.
<<ONLY IF YOU KNOW WHAT YOU ARE DOING - you could take a neutral from an A-leg circuit and a neutral from a B-leg circuit, wirenut them together with a single wire to the neutral bar. It is easy to do this wrong.>>
I don't think I want to fill the panel with wire nuts and pigtails. And if it's easy to do wrong, I doubly want to stay away from that procedure!
Thanks for your input, bud.
-- Bobby G.
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