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

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

Reply to
Tom Horne
Loading thread data ...

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

Reply to
Tom Horne

You could write back to SquareD and ask if there are any ground bars available now that fit your panel.

Reply to
bud--

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?

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?

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:

formatting link
Which had an interesting exchange:

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.

Reply to
Robert Green

Already did that as soon as I found the *left* hand label that specified wire sizes for the panel and the part numbers for aux ground bars. (-:

I'm not too hopeful they'll have anything. In that case, I'll adapt the Cutler Hammer device I have. I'll mark through the mounting holes onto the panel's sheet metal back, drill two small pilot holes and then screw the bar down with self-tapping sheet metal screws. The only remaining problem is that it still doesn't free enough neutral holes in the neutral bar to accommodate the outlets I am installing if I use a bonding jumper between the neutral bus and the ground bus. I end up just one hole short. It's always something!

-- Bobby G.

Reply to
Robert Green

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

Reply to
Wayne Whitney

They've replied (very quickly, I might add!):

"The part numbers PK9GTA or PK12GTA are good part numbers and are available from either retail (Lowes, Home Depot) or from a Square D Distributor."

We'll see what HD has to offer. I need to get some GFCI's anyway, so I hope they have the bus bars and the final pieces of this puzzle fall into place. I suspect the Square D bus bar is going to look very much like the Cutler Hammer one does.

FWIW, Ace has the part and it looks so much like the CH bar that I am going to use what I have:

formatting link
The major different appears to be the spacing between the mounting holes. If I can see mounts for the Square D bar, I might still be tempted to return the CH and use the SQD part, but I suspect it's a drill your own affair for both, so they're equivalent.

-- Bobby G.

Reply to
Robert Green

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

Reply to
Tom Horne

Post your pics at tinypic.com and it will give you a URL to post in a Usenet message.

Reply to
Terry

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.

Reply to
Robert Green

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.

Reply to
Robert Green

Don't get too crazy about this, just splice on another wire the same size with a wirenut

Reply to
gfretwell
408.41 Grounded Conductor Terminations. Each grounded conductor shall termi nate within the panelboard in an individual terminal that is not also used for another conductor. Exception:? Grounded conductors of circuits with parallel conductor s shall be permitted to terminate in a single terminal if the terminal is i dentified for connection of more than one conductor.
Reply to
dcelectricllc

Which most are NOT.

Reply to
clare

Unclear what exactly your point is here. Even if a panel allows more than one neutral connection per screw, the above exception is irrelevant because only very large conductors are permitted to be paralleled, none of which would fit under a home neutral bar screw. And I've never seen a parallel conductor in a home, have you? It's not complicated, the answer is that more than one wire per screw on the neutral bar is not permitted.

Reply to
trader_4

You can only put one neutral in each hole but if they are grounding conductors most panel manufacturers list them for up to 3. It is not really the connection that is the problem. You just do not want to disconnect multiple neutrals to work on one circuit.

Reply to
gfretwell

Agree, my point was that the parallel conductor exception for current carrying conductors raised by Clare was a red herring, because it does not apply.

Reply to
trader_4

I was going to address that but I thought it might just add to the confusion. The minimum size for parallel conductors is 1/0. You do not see many parallel conductors in 1 & 2 family ... Maybe Bill Gates' house

Reply to
gfretwell

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.