mm wrote:
On Mon, 26 Apr 2010 20:42:50 -0500, The Daring Dufas
wrote:

Don Klipstein wrote:
In article , mm wrote:
On Sat, 24 Apr 2010 01:56:57 -0400, mm
wrote:

On Fri, 23 Apr 2010 16:03:45 -0700 (PDT), JIMMIE
wrote:

On Apr 23, 10:07 am, mm wrote:
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?
Sounds like whoever installed the smoke detector may have connected it
to the switch wires for the light.

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. .
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,
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.

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.

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.


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