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.
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.
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?
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
"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?
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:
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? )-:
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
Thanks for your help, Wayne.
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
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.
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
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
[ 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
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.
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
You should be fine with at least doubling up the grounds. If you need more
room add another ground bar.
<<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
<<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
<<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.
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