Sorry if you see this twice. I didn't see it make it out the first time.
Last week I had the Electrical Inspector at my house to check on the central
air conditioning which I had installed at the end of last summer. While he
was there, I took the opportunity to review with him my plans for adding a
sub panel for my shop to my existing service.
My plan is to use the old load center left over from my house prior to
renovations. This already has a 100 amp main breaker and all I have to do
is separate the neutral and the ground in this box. I also explained to him
that I would be adding a 100 amp double breaker to my main box. My main box
has 40 breaker slots (about 3/4s occupied) and I indicated that I would put
the new breakers near the bottom, just below the 50 amp double breakers for
the central air.
The inspector said to me that I might consider moving the higher amp
breakers to the top of the box. That would minimize the lights dimming when
these loads came on. My lights do dim a little when the A/C first starts
My questions then to the learned members of this group:
1. Do you agree that moving of the hi-load breakers to the top of
the box will really minimize the lights dimming when their loads come on?
2. If true then I will move some existing breakers. To do so, I will
have to extend the black wire on some 15 and 20 amp breakers. Are crimp-on
splices acceptable for this?
Marginally so. You are talking about the resistance of the bus bars.
Not unless you have the right crimping tools and the right splices. This is not
the ones you get at Home Depot.
I would avoid unnecessary splicing for a marginal fix to a problem.
You may also be seeing a lot of resistance in the drop and other connectios
that makes the busbar resistance inconsequential. Do what you can do along
these lines where it is easy but I wouldn't introduce one can of worms
(unnecessary splices) to try to fix another one.
It's highly unlikely that moving the high curent breaker will make any
difference in the dimming of lights. This is typically caused by a high
impedance power line. If you have any significant resistance in the buss bar,
in the set up you have now, it would be getting pretty hot with all that
current running through it.
no! the dimming is due to decrease voltage as the higher amps are drawn
(voltage drop). that decreased voltage will be the same over the entire
bus length. that's why they will dim in the house also which is on
another buss altogether and efectivly "higher up" the buss.
this is not worth the hassle of moving breakers and splicing wires.
Bill Leonhardt wrote:
Absolutely! The closer to the main breaker the high load taps are
located on the buss bars, the better.
Not appreciated by some AHJ, and kind of sloppy. A better solution is
attempting to pull some slack from outside the box into the panel and
strip back a little more insulation. But if that can't be done...
On Wed, 07 Jan 2004 15:10:43 -0500, Greg G. wrote:
I'm always amused by this topic, especially when perpetuated by people
who should know better.
Look at it this way: wire resistance is measured in Ohms/100 FEET. The
perfectly legitimate ampacity of 12 gauge wire is 20 amps. That safely
accommodates a circuit length of dozens of feet at that current load.
I don't know the exact cross sectional area of a typical bus in a 200
amp/40 slot load center, but it is a WHOLE bunch more than even 10
times that of 12ga. wire. And it's only a matter of inches long
(probably 18 or less).
I don't think it would be possible to measure the voltage drop on a
typical 18" bus at 1000 amps, much less 100 or 50. You certainly
wouldn't be able to solve light dimming by whatever insignificant
amount it is.
I was shocked (sorry) when I read the recommendation to put the higher
current breakers farther up the bus in a how-to electrical book by a
very respected author. He should have known better.
Master Woodbutcher and seasoned termite
Shamelessly whoring my website since 1999
As my follow up to this stated:
"Some of the cheap contractor-pack load panels are marginal affairs,
and the bus bars are barely adequate for the loads they are rated at.
A high quality service panel *should* show no improvement from this.
But in theory and practice, there are valid reasons for doing so."
I don't recall the statement that he had a 200 amp service, but...
The problem stems from the stab connector to bus interface and the
heat which is generated under heavy loads. The bus bars in some of
these cheaper panels are nothing more than 14 G stamped steel. I have
seen these bus bars get pretty warm under load conditions. In my
opinion, it is better to contain this heat in as little an area as
possible to keep it away from the other lesser connection interfaces.
Not reading the OP's question thoroughly, I probably jumped the gun on
this one. I was addressing the breaker location more than the light
dimming problem. If you are having light dimming problems, your
service or wiring is inadequate, you have a failing, high resistance
connection somewhere along the line to the panel, or the main breaker
could be failing.
It hurts nothing, and possibly helps. When I wire a panel, I do this
for the piece of mind of knowing that everything is as theoretically
optimized as it can be.
I'm the O.P.
First, thanks for all the replies thus far. I'm definitely gonna avoid
A little more background:
1. I have 200 amp service. The main panel, which is new (1.5 years old),
was installed after a "whole house" renovation. The panel is the Square D
"home special" (I think that's the name) you see at the Borg. It could have
a "thin" buss.
2. I have all new circuits, not heavily loaded, and had no dimming prior to
the A/C installation.
3. The dimming I do get with the A/C starting is momentary, not continuous.
4. The A/C has a 50 amp double breaker.
I appreciate LRod's point about the high conductance of the buss and then,
theoretically the light circuits higher up from the A/C on the buss
shouldn't be effected by the A/C. I can also kind of imagine that when the
A/C starts, there is a voltage wave (like a pressure wave in piping) that
might cause a "disturbance" in the circuits it passes in the main buss.
For now, I'm gonna investigate where I have wire slack and consider, where
possible, locating the higher load breakers higher in the box.
Again, thanks to all who responded.
Buy a hard-start capacitor for your AC compressor. My old unit was
causing no problems, but when I bought a new AC unit, the house lights
would nearly go OUT when it kicked in. I checked all the connections
and everything was OK. I went to an AC supply house and bought an
add-on capacitor. I think it was less than $20. It's about the size
of an orange juice can with several wires sticking out one end. It
comes with layman's directions to hook it up to the compressor wiring.
Now I get just a tiny flicker of the lights.
I should add that is hardly worth the trouble in an existing box if
the wiring isn't long enough to reach. This is something that is best
done when the panel is first installed and wired. Some of the cheap
contractor-pack load panels are marginal affairs, and the buss bars
are barely adequate for the loads they are rated at. A high quality
service panel *should* show no improvement from this. But in theory
and practice, there are valid reasons for doing so.
If you cannot rearrange things without splicing, I wouldn't do it. As
mentioned, many AHJ frown on this practice. The lesser of the two
evils is leaving things as they are. You need heavy crimp ferrules
and a tool to install them with. Then you have to worry about the
connection's integrity and the insulating tape unraveling if you don't
use good heat-shrink tubing.
Its scary when people like this have inspectors jobs.
Horse-hockey. If your lights dim when something kicks on or off then the
light circuit itself is a little overloaded to start with or you've got some
connections that arent as good as they should be. Ex. too many lights on one
circuit, other items on the circuit with the lights that shouldnt be like
receptacles, disposals, dishwasher and such, wire size too small or breaker
too small for the said circuit. I have a simliar setup to the one you
described and my lights never dim. Even with machines going in the shop,
central air in the house, electric water heater and so on.
A big no no. If you still want to do this procedure and the wires arent long
enough then..................dont do this procedure.
Wait a minute guy's. Why the big no-no on crimping the wires to extend
I ask this since it was last year when I purchased an emergency generator
and asked here about how they wire up the CB panels for the generators and
... asked the local utility for advice.
Both came back with using wire nuts inside the panel was ok and per code.
This is the same thing electrically and using wire nuts - not crimp-ons and
So did the world change while I wasn't looking?
I dunno. :) "Code" requirements _do_ vary.
At least as of the 1997 NEC, any sort of splice in wiring _inside_ the
breaker panel was verboten. OK in a junction box external to the panel.
Cannot run secondary wiring _through_ the panel, either.
Can't even run two wires to a single breaker.
Cite that, as soon as you can find a 97 NEC (they were 96 or 99)
What the code really says (312.8) is you can't use circuit breaker enclosures
as "junction boxes, raceways or auxilary gutters" and that splices made in
these enclosures can't fill the wiring space at any cross section to more than
40%. The total conductors, taps and splices can't occupy the total wiring space
more than 75%.
In layman's terms that means I can't bring branch circuit conductors back into
the box for a splice and go back out to the load but if the splice is in the
conductor that terminates in the panelboard it is OK. With that said most
inspectors won't let you go crazy in there since those 40% and 75% are going to
be more of a judgement call than a physical measurement.
Depends on the listing of the breaker. <example>Square D QO breakers are listed
for 1 or 2 conductors. If there are 2 slots, one on each side of the screw it
is usually listed for 2 wires. That should be on that tiny label on the
thank you for the last 2 posts, I watch a lot of these electrical posts
and am amazed the "information" that is passed off in here. As an "old
time" electrician (not knob and tube though) I assumed the code could
have changed but did not see any logic in prohibiting splices in the
panel. After all it is just another big metal box.
While not strictly forbidden, a lot of inspectors don't like
to see it. I can see their point in new construction. Splices
in the breaker box smacks of sloppy workmanship if it's new
stuff. Accomodating changes is another story though.
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