Fluorescent fixture won't turn off completely!


A friend tells me that, The two fluorescent bulbs in the furnace room were were doing what they do in old age. After the electrician had installed AC-connected smoke detectors, I saw that the light was partially on even when switch off. So I disconnected the fixture.
And he wants to either fix it by replacing parts or install a new one.
For once I know the project beforehand and can ask your advice beforehand, since I certainly don't know what to do.
How can it be partially on when the switch is off? How can disconnecting the fixture be more effective in turning it off than just flipping the switch?
It didn't used to be like this. Certainly the new AC smoke detector doesn't have a magnetic field strong enough to make this happen.
Advice?
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Fix the wiring. It sounds like the neutral is being switched and there is another (fault) path to ground somewhere. This is a dangerous situation, to say the least.
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mm wrote:

Florescent fixtures will glow like that if the neutral is switched instead of the hot wire. The electrician took a shortcut to keep power on the smoke detectors and that is the result. Not very professional, I wonder what other shortcuts he/she/it may have taken?
TDD
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wrote:

Yup sounds like might be dicey wiring, possibly a wiring shortcut to avoid another connection and/or create a situation where other work will have to be done and paid for! One does wonder what 'other' shortcut the electrician MAY have taken? Possibly wiring the smoke detector between, say live and ground????????????? To avoid running another wire? Either get another electrician or get that one back at no extra charge; then have the smoke detector disconnected and the light switch operated in such a way that the 'live' lead (usually black or occasionally red) to the fluorescent is clearly being switched off/on. Have this fact proved using a light bulb. Might be a remote chance something else is happening! Smart to notice and ask the question; congratulations to the OP.
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The Daring Dufas wrote:

I have an old, old florescent lamp on my desk, the type that has two momentary buttons. A red start button instead of a starter and a black button to turn it off. I didn't open it up, but I think the Black/Off button switch is NC (normally closed) and just breaks the circuit while depressed and letting go of the off button again completes the circuit, but it needs the start switch again to warm the filaments to light. Now and then I'll brush up against it and it will light dimly. You gave me an idea. I'm going to try reversing the polarity by turning the plug 180 degrees and see if it still happens.
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Tony wrote:

I love those old desk lights, I think I have one in storage. With the right lamps, they're great for doing close detailed work.
TDD
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Sounds like whoever installed the smoke detector may have connected it to the switch wires for the light.
Jimmie
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On Fri, 23 Apr 2010 16:03:45 -0700 (PDT), JIMMIE

Thank you, and Keith, Dufas, and Terry. You all agree on the problem. That' pretty good. I"m going over there on Sunday, and for once I'll know something before I get to a project. I'm curious to see what can be seen, and they'll give me lunch. I may just call him and tell him what you said, to save myself time, but I really do what to see what the ee-leck-trishon did, if I can. .
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wrote:

Well, my friend forgot he had to go to a concert! so I only spent about 5 minutes there. The electrician came highly recommended and my friend called him today and the elec. said he hadn't done anything wrong like that.
There seems to be no particular reason to think the wires to the light were fiddled with because it looks like all the wires are right there. The hot is as accessible as the neutral.
It was a round junction box, packed with 5 pieces of Romex**. On the ceiling, and I only had a few minutes so I didnt' tug them apart, or measure anything. Will go back with more tools and more time and a radio to keep me company later this week.
**Power in, ceiling fluorescent out, switch for fluorescent out, closet ceiling light out, and new wire to CO alarm and Smoke Alarm out,
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I would see if the ground wire of the romex cable going out to the switch got disconnected from ground.
With the ground wire ungrounded, or with 2-wire romex (older installations), there is enough capacitance between the hot and neutral to allow easily tens of microamperes of current to flow through.
120V fluorescent fixtures with bulbs up to 22 watts and series inductor ballasts sometimes continue to glow very dimly from this after being switched off. At least usually, only one bulb on the same switch glows from this low current. If more than one bulb is glowing, chances are the cause is something else, such as nearby high voltage AC or high voltage pulsating DC or a fairly powerful radio radiation source.
Although dim glow is often hard on the filaments, this very low amount of current (flowing through a switch cable) appears to me to be fairly harmless. However, I cannot guarantee that this will not shorten the life of the bulbs. Meanwhile, if the switch cable's ground wire is not connected to ground, then get that fixed. The ground wire is there for safety purposes in case of the unlikely event that the hot wire contacts the switch box.
--
- Don Klipstein ( snipped-for-privacy@misty.com)

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In wrote:

The filaments are not lit; the missing ground simply never allows enough bleed down to stop the glow of the gases.
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Don Klipstein wrote:

I forgot to ask if there was a lighted switch hooked to the fixture. Folks have had problems with certain equipment when it was hooked to a lighted switch.
TDD
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On Mon, 26 Apr 2010 20:42:50 -0500, The Daring Dufas

No lighted switch. Just a regular toggle.
When it wouldnt' stop glowing he disconnected the fixture and it appeared that there were three wires, two wires and a ground, but I didn't measure any voltages. So I can't tell you more about it, and I don't feel like going alone after all so I won't have more to report until after Friday or maybe evne Sunday. I should probably start a new thread then, because that will be 600 or 800 posts from nowr.
Thanks again, to all.

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mm wrote:

Back in the late 1980's I worked at The Kwajalein Missile Range for a contractor who was building, among other things, the new mission control center for SDI. We had a number of native people, The Marshallese working for us. A smattering of the 2'x4' lay in fluorescent light fixtures had battery backup built in. One of the fixtures was disconnected, leaning against a wall and was lit up with the MC cable dangling loose behind it. A group of our Marshallese help were gathered around the light pointing and excitedly jabbering in their native language while one of them picked up the disconnected power cable, looked behind the fixture and scratched his head in complete bewilderment. It was hysterically funny.
TDD
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On Apr 28, 12:22am, The Daring Dufas <the-daring-

A Navy friend said that when they saw a worker carrying an arm load of 8 foot fluorescent tubes across the tarmac they momentarily aimed the RADAR at him...when they all lit-up...I'm sure you can guess where the went...straight up! bob_v
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Bob Villa wrote:

If it was at dusk or on a dark day, it would have been quite effective.
TDD
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In wrote:

That's a classic symptom of a missing ground for the fixture.
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