I got to use my
volt tester twice today, which is good, because I carry it
around all day in my
pocket
protector; but bad, because I only use it if I'm not sure an
action that I am about to take will kill me or not.
I replaced a socket in a fluoro can light; because when one of the
lights burn out, in this particular type of fixture, the other
socket then gets hot enough to melt to the folded tube's plastic
base, but
not hot enough to trip the thermal protection
fuse. When the second lamp dies of accelerated old age[1], you get
up there (on a 10-foot ladder,
of course) to discover that
the lamp can't be changed without pulling the entire fixture apart
and replacing the socket.
All this means that every time I walk through the lobby I have to
stare up at ceilings, hoping to spot a light out. I can't just look
for dark cans, since there's
two bulbs per fixture.
Thanks, whoever designed this bastard. Thanks a lot.
However, replacing the socket requires shutting off power at the
panel, since there's no service disconnect inside the fixture (not
enough room) nor on the junction box feeding the fixture.
(prohibitively expensive) However, again, this means shutting off
the lights in a elevator lobby, so repairing the fixture is best
done with
haste.
Guess who
didn't manage to repair it with haste? Me.
Vlad had been sitting on this fixture for a couple of weeks, hoping
that nobody would notice that it was only holding one bulb, but
eventually that bulb went out, (Two days after he retired, of
course.) and I had to go up and change it. He had told me, quite
clearly[2], which breaker controlled that bank of lights, so I
switched it off, and screwed on the fiddly little circuit breaker
lockout to ensure that nobody would flip it back on while I was at
the top of a ladder[3]. Walk back out to the lobby, and discover
that, nope, that's the lobby
entrance lights, and hey,
wow, looks like emergency exit lights start blinking when you cut
off their power!
So I start flipping each breaker with the word "lights" in its
tag.
Breaker 2? 6? 11? 31?
Ah, that's the ticket.
Replacing the socket was uneventful, (checking it with the volt
tester to make sure it was off, returning to the topic) but turning
the power back on revealed that shutting the power off at the
breaker was traumatic enough to kill lights in two other
fixtures.
The second time I used the volt tester was while replacing a
ballast. The work order had been for a light out in Reception, and
in the employee kitchen. The reception bulb was a weirdo, a BR base
(incandescent floodlight form factor) compact fluorescent; (model
number
CF16BR30, in case you care) but in the kitchen, all four lights
in the fixture were out, which is pretty damn rare. Engaging in
some forensics while waiting to see if the lights would burn
out[4], just working off the dates, it looked like three of the
lights went out, and the fixture limped along with one for a couple
of years (!) before the last one went the way of its
brothers.
On my way out, I noticed some lights out in the secretarial quad,
and after getting authorization,[5] I started changing them. One
fixture with both lights out
did have a bad ballast,
(which required using the volt tester for the second time) and by
the time I left I had gone through 12 tubes, about half a
case.
After dropping my cart off at my office, I went down to the loading
dock to get some of those chocolate wafer things, when I discovered
that we were in the process of having a new vending machine
delivered. The guy had just finished testing it, so I offered to be
the first customer.
The vending machine had an XY (rather, YZ, since it didn't traverse
the
depth of the machine, ah ha ha ha) gantry, with a
basket and a motor on it. The gantry would move over whatever row
you selected, the motor would engage a sprocket on the front of the
row, and vend whatever you selected. I put my money in, it goes
through its song and dance, and nothing happens. The gantry resets
and repositions itself, nothing happens. Gantry moves back to the
bottom row, and now the display reads "SELECT ANOTHER
PRODUCT".
Vending machine guy: Huh.
Me: At least it didn't steal my money.
Some troubleshooting later, we figure out that the row itself
wasn't positioned correctly. Pop it open, fix it, now it vends
correctly. Get back to my office, and the mountain dew's warm,
since he had just put it in.
ALL I GOT IS PROBLEMS
1: The typical end-of-life failure mode of a fluorescent lamp is
failure to achieve
discharge
due to insufficient gas ionization, which is in turn due to cathode
failure, high gas pressure, or incorrect gas mixture.
The electrode filaments on fluorescent tubes are great big beefy
things, especially compared to the ones in incandescent bulbs,
which have to be thin thanks to physics; but the therminonic
emission "catalyst" (not literally a catalyst, since there are no
chemical reactions occurring) coating on the cathode filaments
still boil off fairly briskly. Some of these newly liberated ions
will slam right into the side of the tube, producing the dark spots
on the ends of old fluoro tubes, and, eventually, cracking them;
allowing the atmosphere in, which both changes the composition of
the gas, and raises the pressure high enough to extinguish the
discharge, but the rest of the ions are lost forever.
This is bad, because the coating is what enables the discharge, and
when enough of it boils off, the lamp won't light, or, in
borderline cases, will only light when cold. This causes the light
to turn itself on and off (the electronics will manage to light the
lamp, but internal pressure will rise as the lamp warms up until
the electronics can't supply enough current to sustain the
discharge, at which point the lamp turns off, rinse, repeat) until
the temperature cycling boils enough catalyst off to kill the lamp
dead. This doesn't occur very often in fluoro tubes, since they
start so quickly; but is fairly easy to observe in aged low
pressure sodium bulbs; since they warm up slowly, thanks to their
greater mass.
The
point being, heat kills fluorescents, and keeping them
hot kills them faster.
2: Lit. "Looby lights, they are controlled by breaker von on panel
seeven. I am Russian, despite how bahdly Sam is mangling my
accent!"
3: Being shocked at the top of a ladder usually results in death of
falling
off a ladder.
4: In almost every case, an entire fixture going out means the
ballast's bad. So far, I've only seen this failure mode
twice.
5: Some tennants like to leave fixtures half-populated, to save
energy, and to confuse poor lighting fixture maintenance personnel.
On these occasions, I only change lights when
directly
asked by the person
sitting closest to the
fixture.