Flickering Lights and Buss Arching

I've been in my home almost 10 years and all of a sudden, a single circuit in my home started to flicker and intermittently power on and off (the breaker never tripped). I've done electrical work in the past when I finished my basement. The first thing I thought of was to replace the breaker. It's a Cutler Hammer twin (slimline) 15A breaker.
After replacing it, the problem still occurred (so it was unlikely it was the breaker). After some diagnosising, I noticed that there was some arching ocurring in one of the terminals on the neutral buss bar. I tapped on the panel, and a small spark shot from the terminal. I turned off the circuit in question, and the arching and spark ceased. I then knew that the arching neutral belonged to the circuit in question.
I found it odd that there are one or two ground wires on the neutral buss bar. However, the neutral buss bar is right on top of the ground buss bar. Don't they go to the same place anyway? Is this odd or OK? I know I've seen some panels where the ground buss is totally separated from the neutral buss.
This neutral wire is sharing the same screw terminal on the buss bar with a ground wire from another circuit. I shut off the main breaker and screwed down the terminal firmly which fixed the problem. However, 5 days later, it started happening again. No sparks fly when I tap on the panel, but there is slight arching in that same termAinal.
Just eyeballing it, it looks like my neutral is a 14 gauge whilst the ground in the same terminal might be a 12 gauge which would explain why the neutral is not secured enough by the screw terminal. I am going to to shut off the main breaker do some housekeeping on the terminals making sure the same gauge wire is shared by neutrals in the same terminal.
1. Does it look like I've diagnosed the problem and I'm taking the correct measures to fix it?
2. Why would this happen all of sudden after 10 years of living in the home? The terminal screw didn't seem all that loose when I tightened it the first time. I barely got 1/16 to 1/8 of a turn on it.
3. Is it OK for neutrals and grounds to share the same terminal on the neutral buss bar? Of different or same circuits?
4. Any other comments to add on what I've described?
Thanks,
Jason
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Sounds like that terminal is a bit loose. Did you tighten it?
And is this copper wire, or aluminum?

It's OK, as long as this is your main panel. Neutral and ground are required to be connected at the service entrance (main) panel, and required to *not* be connected anywhere else.

That is *not* OK unless the terminals are specifically listed for use with more than one wire. If they are, it will say so on the label inside the panel access door.

Better still to use only one wire per terminal.

Diagnosed the problem, yes. Correct measures to fix it, probably not. The best fix is one wire per terminal (unless the terminals are specifically listed for two wires).

Copper or aluminum wire? This is VERY important.

As long as we're talking about a main panel, not a subpanel, and the terminals are listed for use with two or more wires, that's fine. Since the neutral and ground are electrically continuous in the main panel, there's no problem electrically. Mechanically, you may have a problem attaching multiple wires securely.

If this is aluminum wire, you have to be *very* careful not to overtighten the connections.
--
Regards,
Doug Miller (alphageek at milmac dot com)
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Thanks Doug,
This is copper wiring. I do notice on the buss bar that there are two sizes of screw terminals. The ones containing two wires are of the larger size. However, the point is taken. When I do my "housekeeping" on the panel, I will try to keep it one wire per terminal. It does look like, however, that there may not be enough terminals for each circuit to be in it's own, but I'll get a closer look. The last time I worked closely with the panel is when I installed a 50A breaker and wired in a sub-panel for my finished basement.
It definitely seems like a poor connection on the buss since it worked fine for a week after tightening it. However, this morning it was back to flickering and arching.
Thanks for your help.
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daokfella wrote:

That may be indication of other connections on the circuit having similar problems, too (although I guess you're seeing arcing at that same neutral in the box so that would definitely be a problem).
See my other response on cleaning terminals and wires to remove corrosion/oxidation. If the wires have been flattened by previous connection might snip off to a new end if have a little slack. Moving one or more to alternate location on the neutral bar is a possibility although shouldn't be necessary unless the arcing has significantly damaged that connection location. It is likely that if there has been sufficient arcing you have seen it that it has caused some oxidation of the surfaces. If so, may not be making good contact even if you did retighten connections.
Whatever, don't give up until resolve it as (I'm sure you're well aware) this ain't good...
--
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If you have to put two wires into the same terminal, either try to keep the wire gauge the same so that the pressure is the same on both wires, or twist the wires together before inserting into the terminal, which may be difficult to insert the twisted wires without them untwisting, but you will get a much better connection with equal pressure on both wires.

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Doug Miller wrote:

Neutrals must be 1 per terminal - 408.41. [From an RBM post]
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Didn't know that. Thanks.
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Doug Miller (alphageek at milmac dot com)
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Doug Miller wrote:

Grounds, however, may be more than one (three I think?)
nate
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Nate Nagel wrote:

I didn't know until I read RBM's post. Amazing what is lurking in the NEC. In any case, as you said, the panel label will indicate what is allowed.

RBM also wrote: "UL Std. 67 (Panelboard Standard) permits up to three 10 AWG equipment grounding conductors to terminate on a single terminal, if the terminal is marked for this purpose."
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daokfella wrote:

What Doug said plus...
2. Time is the key along w/ load cycling and relaxation/compression of the conductors. Things gradually tend to loosen some over time. Particularly, if a small amount of corrosion begins, that acts as a small heater and then it is a progressive thing w/ a positive feedback--more heat leads to more thermal expansion/contraction and corrosion which causes more loosening and so on. Very slow initially, but eventually troubles become apparent.
4. As Doug says, depends a lot on whether this is copper or aluminum wiring.
Either way, my recommendation would be to also turn power off and take the affected circuit(s) neutrals free from the bar and check carefully for signs of oxidation/corrosion on both the wire end(s) and the connections and the screw. Shine 'em up a little can't hurt.
If it's Al, connections need to be made w/ anti-oxidant lube--I'm assuming probably aren't or would have been mentioned, but if are, that's critical as Doug says.
I would also do a routine check for tightness of all connections in the box at the same time -- you might find a couple of others that aren't as tight as they might be.
And, of course, examine all wire ends for any signs of excessive heat just as a precaution since you're in there anyway...
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daokfella wrote:

Hmmm, First thing you'd do is checking for loose wire(hot, neutral, ground) for that circuit. At the panel neutral and ground is same.
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daokfella wrote:

One terminal, one wire is the rule. Go to an electrical distributor outlet and buy an additional buss bar for your panel. There are often pre-tapped mounting holes for the new bar in the enclosure. Mount and bond it to the other busses, then segregate your neutral and ground wires to single occupancy. Cost should be under $10 unless you're driving a giant SUV to the store. HTH
Joe
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Electricity should never arch. It should spark in a straight line, not arched. If your electricity is arching, that's not good. Curved like the golden arches (McDonalds) isn't normal. Have you checked to see if the power company is selling you straight electricity, or the new curved kind?
As to resolving the arcing, since you're already in the panel box, how about shut off the breaker, and put the neutral into a different hole, in the neutral bar? Then, screw it down snugly and see if that helps.
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Christopher A. Young
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Stormin Mormon wrote:

...
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