"Tom Horne" wrote in message
news:jDH9j.9717$c82.8181@trnddc01...
Robert Green wrote:
"The Freon Cowboy" wrote in message
m...
yes, its permissible, and done everywhere .
FWIW, it looks like the reason it's done everywhere is that the "by the
book" solution is pretty drastic. As far as I can tell from what Square
D
said, to gain more neutral holes, I'll have to change out the whole box.
That's a little too drastic a solution and I have a few options. One is
to
disconnect the central A/C since we never use it. That would free some
openings. Another is to mount the supplemental Cutler Hammer ground bus
bar
in the case, feed it with a large diameter wire from the existing
neutral
bus bar and move the three or four ground wires now connected to the bus
(old house, very few grounded outlets) to the supplemental ground bus
bar.
The third seems to be what most people do. Put two wires under a
setscrew
and print up a big label for the box "Disconnect Main Breaker Before
Neutral
Rewiring!"
--
Bobby G.
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'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
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.
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?
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.
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/archiv...hp/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.