Neon light exploding and falling from fixture

What would cause a neon light to suddenly explode and fall from its fixture? There was a buzzing sound before it happened. It was two 6 foot long neon tubes that both basically exploded and came crashing down on the floor. I am afraid to replace these tubes until I know this will not happen again.
Has anyone ever had a neon light fixture do this?
Lesley
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Neon fixtures use very high voltage. A short circuit in the fixture could cause this. What is this being used for?

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Lesley wrote:

Were you there and observed them when they exploded?
If not, is there a possibility that somebody or something came into the carport and bumped into them?
Jeff
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I've never seen or heard of that happening. If these lamps are in fact fluorescent, and six feet in length, that in itself is an uncommon fixture. Common lengths for fluorescent fixtures are four feet and eight feet. A six foot fixture could be a hybrid and need special lamps

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I've had it happen in our warehouse. There is some vibration from the floor above though and it is still a rarity. I can think of maybe two times in 15 years with a couple hundred fixtures.
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"carport" suggests it's not truly cold there but if you do get sub-freezing temperatures there, you may want to put in regular screw-in light bulbs since they work no matter what the outside temperature is. Flourescents don't like cold weather. Yeah, there are flourescent fixtures designed for cold-weather use, but not extreme cold like I get here in Montana.
If you want to hang on to the flourescent lights, maybe replace the ballasts with electronic units. They don't buzz at all, at least not the kind you get at the electrical supply houses (not Lowe's, Home Cheapo, etc) and they run cooler, which means they're more efficient and use less electricity.
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On Sun, 12 Aug 2007 14:01:30 -0700, "Lesley"

I thought you meant florescent. You cant change the tubes on a neon (without special equipment anyhow).
Anyhow, when I was a young boy I was in a store with my father when a florescent bulb exploded. Both of us were covered with glass and florescent dust. The store wanted us to go to a hospital but my father said we were ok. I will never forget that. As a youngster it was quite frightening.
I'd suspect the ballast is bad. I'd replace the ballast if I were you. (or the whole fixture). But all you really need to change is the ballast. The rest of the fixture is just a metal shell and some wires, plus the lamp "sockets". Unless the bulb fell out of the socket, there is nothing else that could cause this except the ballast. You said it exploded in the fixture, so that eliminates the falling out of a bad socket.
I am glad this does not happen often considering how many places have florescent lights. I think those old "transformer" type ballasts were more likely to fail than the modern electronic ones. This dont happen to be one with the old twist in starters, is it?
Jim
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jamesrdens@ya_oo.com wrote:

It would be helpful if Don Klipstein jumped in and educated us about what sort of ballast failure causes a flourescent bulb to "explode".
My understanding of ballast operation is that aside from heating the filaments for starting their main purpose is to act as a "choke" which provides an inductive impedance to drop line voltage down to the voltage level which is correct for the particular bulbs they are rated for.
A fixed resistor could provide the same voltage drop, but would waste too much power as heat. Back around 1949 my uncle Mo, who was well versed in electricity and the electronics of that era made me a line voltage operated "black light" from a small UV flourescent bulb and a big wirewound resistor, all housed in one of those wooden Velveta cheese boxes about 10 inches long. (Rememvber them?)
So, maybe if the "choke" in the ballast which provides that inductive reactance in series with the bulb were to short out, the bulb would receive full line voltage and the resulting arc would be so intense that it could overheat the gas in the tube causing its pressure to increase enough to burst the bulb. Or, maybe it would just run so hot that the heat would precipitate a mechanical failure.
Just my .02, but I've got a feeling that if the OP didn't know the difference between neon tube and a flourescent bulb then he/she may not be able to judge the length of the bulbs "by eye" either. So let's not get too worked up trying to figure out what's really installed there and what went wrong.
Me, I'm down to telling the OP to get a qualified pro out there to check things out, I wouldn't dare suggest that the OP tries working on it him/herself.
Jeff
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The gas in most fluorescents has a pressure at room temperature in the 2 mm Hg ballpark, roughly .2-.3% of atmospheric pressure. I don't see much chance of one bursting from overpressure if the ballast shorted.
As for how I suspect a fluorescent lamp could explode? Or more likely implode since the pressure in one is most of the way to a vacuum?
This gets a bit towards grasping at straws...
1. Very serious ballast failure sends a few amps through the bulbs, the electrodes melt and the arc terminates on the lead wires, the leads melt down and the arc terminates on lead stubs where the leads pass through the glass, the glass overheats and cracks, then the bulb breaks and implodes.
I never heard of this actually happening. Most ballasts can't do this anyway:
a) The usual magnetic rapid start ballasts for 4-footers have current limiting by leakage inductance caused by magnetic shunts in the core. No short can defeat that. Shorting of part of the primary will increase output, but not by a whole lot before the ballast overheats so badly as to just burn out.
b) In any magnetic ballast, the windings will normally melt and work as a fuse before such a high amount of current can crack the bulb.
c) I don't see much chance of an electronic ballast malfunctioning in a way to put out that much current without conking out before the bulb can break.
But if the ballast is an old lead-lag type that makes bulbs flicker out of phase with each other, I am not as confident that it can't break a bulb if it shorts, especially if a capacitor shorts.
2. The ballast blows up and spits out shrapnel that breaks the bulbs.
This sounds awfully improbable to me.
One day I was close to a ballast that did go "Pow" and spit stuff out. This was one of the maybe 1,000 or at least a few hundred or so ballasts for the fluorescent lights in the ceilings where I worked then. The bulbs were 8-footers. The ballast started humming, then a few aseconds later the hum changed to a louder buzz, and after a second or two of that the ballast went POW! There was a small hole blasted in the metal ballast case. I suspect a localized small region of the tar poured into such ballasts boiled due to a short. If whatever blew out the hole hit a bulb, I suspect that could have broken the bulb.
This is fairly rare, and normally in fluorescent fixtures there is metal fixture material sorrounding the ballast.
3. Some instant start fluorescent fixtures have ballasts that put out enough voltage to refuse to take "burned out" for an answer. I suspect this is more likely with instant start ballasts rated for more than one bulb length and running a shorter one, if the ballast is rated for cold temperatures, or running a bulb that is shorter than the ballast is rated for. If the electrodes get worn out, the ballast provides enough voltage to maintain the arc in the bulb anyway. Possibly the arc can melt down electrode leads all the way to the glass and then crack the glass. Also, sustaining of an arc on electrodes that are in no shape to do so my occur, and the electrodes get much hotter than normal doing so, and the ends of the bulb may overheat and crack.
I would give this increased chance if the bulbs are those old "slimline" ones with only one pin on each end.
I have seen this occur with 32 watt 4-foot T8 (1 inch diameter) bulbs with instant start type electronic ballasts, especially in fixtures with the ballast running at least 2 bulbs (pseudoparallel arrangement in ballast, where patrt of the current limiting is common to all bulbs and part is applied individually to each bulb). When one bulb dies, the remaining one(s) get(s) a little brighter. When the last bulb dies, the ballast sometimes keeps it working by brute force. I have seen a few bulbs where the glass cracks in the region of the bulb around one filament. So far, I have only seen cracked bulbs and not imploded ones. However, I have heard of lampholders (sockets) burning up if they are not high temperature ones rated for this kind of heat.
Warning signs: Bulb flickers, one end (less frequently both ends) is blackened, and the failing end may have purplish/pinkish flashes or pinkish/orangish/orange-incandescentish glow. The failing bulb should be removed unless you are confident that your fixture is fully tolerant of whatever can happen there.
Bulb failure is much more of a non-problem with rapid start ballasts than with instant start ballasts. Meanwhile, I'm sure that the manufacturers have done things to mitigate bulb failure problems with instant start ballasts for T8 fluorescents of 17-32 watts.
4. The ballast failed or malfunctioned and vibrated, or posibly just got loose and vibrated, or external vibration shook the bulbs out, and bulbs fell out of the fixture and imploded upon landing.
- Don Klipstein ( snipped-for-privacy@misty.com)
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Neon or fluorescent?
I'd suspect a power surge or failed power supply.
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Sorry. I meant fluorescent.
Lesley.
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Lesley wrote:

Perhaps the ballast failed. That would account for the buzzing, too.
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Lesley wrote:

Uh, are you sure you know the difference between a neon light and a flourescent bulb, Lesley.
Neon lights are usually not in "fixtures" znd used for lighting to see by, they're used on signs, and are held in place pretty well by lots of clips and permanent wiring.
Please clarify what the "fixture" looks like and maybe we'll understand for certain what it is and be better able to help.
Jeff
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Lesley wrote:

If one drills a small hole in the end of a florescent bulb, then administers about a tablespoon of gasoline into the tube, then when the bulb is energized one gets an explosion of totally immense proportions.
That's probably not what happened in your case.
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