help - simple electrical question


I have under-cabinet fluorescent lights. Two light fixures in parallel, wired to one single pole switch. Each light fixture consists of 2 13W tubes, driven by a "ballast". (So, the total rig consists of 1 switch, 2 ballasts, and 4 fluorescent tubes).
Today, 3 out of the 4 tubes went dark. Long story short, all is well after I replaced only *one* tube. That one bad tube had caused both tubes in 1 fixture to go dark, *and* one tube in the neighboring fixture. (?!)
Anybody know what's going on?
Bill
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Mr_Bill wrote:

To be honest, I don't have a clue as to how flourescent lights work. However, I always replace all the tubes in any fixture that fails. To do otherwise seems like a total waste of time.
In regards to the second fixture, I would think that there is something coincidental going on. Assuming a good parallel connection, it strikes me as an impossibility that the one fixture could effect the other one (except for a short circuit situation).
There is a remote possibility, I suppose, that if the voltage is marginal, the power factor of the failing fixture's ballast could be dragging the power down on the other fixture. That seems kind of far fetched, though.
Do you have an evaporative (swamp) cooler by the way?
Have you tried removing the tube again to see if you can reproduce the failure?
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all the lamps are near the end of their life. all have the same number of hours, and same number of off and ons. most likely all tubes are darkened at their ends.
always replace all lamps in a mixture.
bottom line you will be needing more lamps soon........
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snipped-for-privacy@aol.com wrote:

Poor analysis, and doesn't fit with the facts. He said he replaced one bulb and all is fine.
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I have about 25 fluroscent fixtures here. bulbs act flakey, replacing one bad one often gets the other lamp working temporariliy.
after all asuming they were new and all installed at the same time their end of life should be similiar.
the other fixture is likely a fluke........
big question are bulbs ends dark?
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snipped-for-privacy@aol.com wrote:

fixes the problem but that is with shop lighting fixtures. The other fixture may be a fluke but the problem is likely to be some kind of interference from the first fixture.
In any case, replacing tubes in small under counter fixtures is often/usually a waste of money. The tubes often cost more than a fixture with tubes and the fixtures seem to suffer from heat exhaustion. I suppose it is due to the production numbers (high numbers lower costs) but the little tubes are very costly compared to regular 4 foot tubes.
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Mr_Bill wrote:

Pretty sure!
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Mr_Bill wrote:

I'd guess they're not properly wired in parallel.
Chris
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First, to restate the problem. I have 2 FSC3024 undercab lighting modules. Each module consists of 2 8W T5 flourescents and a single (complex) electronic ballast. These 2 FSC3024's are wired in parallel and run back to a single pole switch. One T5 tube went down, and brought down the other tube in the same 3024 module and one (?) of the tubes in the other module. When I changed the one bad tube, everything lit up. Everything ran ok for 1 yr before this happened. The switch is a Lightoleer MSP600NDW, one of those fancy-pants switches (non-dimmer) which is controlled by a "master" over an ASCII bus, and which can be manually overridden. When 3 out of 4 tubes were dark I bypassed the switch, hardwiring to "hot". No change, i.e. 3 out of 4 tubes still dark.
The wiring isn't exactly rocket science, but anyway I checked the voltage to each ballast and it reads 119.6vac from hot to neutral, both when the fault is showing and when everything is lit up.
I was hoping someone had encountered this before.
My only theory is that the electronic ballasts are of a lousy design, and that they "crosstalk" to each other, i.e. they put out some kind of noise spikes, especially when the load on the ballast drops below 16W.
Has anyone seen this type of behavior before. Have you had trouble with FSC electronic ballasts?
Bill
Chris Friesen wrote:

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Put the "bad" tube in and out several times to see if the three others always fail to light when it is in. It is common for two tubes on a common ballast to go out when one tube fails or is removed. I strongly suspect that the other two tubes going out was caused by something other than the one bad tube. Poor grounding of the metal reflector can cause some rapid-start tubes to not light.
Don Young
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