In article m, David
Nebenzahl wrote:
On 1/22/2009 5:25 AM Don Klipstein spake thus:

In m, D. Nebenzahl said:
On 1/21/2009 8:06 AM TimR spake thus:

One thing sure, four tubes didn't reach end of life at precisely the
same time.

True; but if it has a newer electronic ballast, it may shut down all 4
bulbs if it senses that one of them is going out. Might be worthwhile
trying new bulbs first.

My experience with electronic ballasts for fluorescents is that they
don't do that. All bulbs going out at the same time is usually (in this
order) a bad connection, ballast failure, lack of grounding, or very
unfavorable conditions (sometimes including bulb-ballast mismatch).

Are you sure about that? I ask because I recently had a problem
installing a new ballast in a fixture; I connected it the way I thought
it should work, but it wouldn't light what I knew were good bulbs. (I
had connected the two leads to each bulb's end together as the old
ballast had been wired.)

Take a good look at the wiring diagram on the ballast - it may be
different from what you had before.

I called the manufacturer's tech support line,
and they advised me that I had to connect it exactly as shown on the
diagram, because the ballast incorporated a protection feature (I forget
the exact name of it now) that sensed when a bulb was about to fail and
then shut down both bulbs, rather than allowing them to flicker.

This was a 2-bulb ballast; not sure if this would apply to a 4-bulb
fixture, but it certainly seems possible.

OK, maybe true, though my experience is that this was typical of 2-bulb
magnetic ballasts, and that the 2-bulb electronic ballasts at my workplace
do not shut down when either or both bulbs have at least one foot or
both feet in the grave.

There might be some new safety feature, but I think the problem that
would solve is from the last bulb burning out. In a "pseudoparallel"
multiple bulb electronic ballast, when the last bulb is dying, at least
one end of the bulb usually gets awfully hot, sometimes cracks from the
heat. Sockets from before electronic ballasts became common may be unable
to withstand that heat.
Bulbs other than the last one, when in the process of burning out,
usually have at least one end getting fairly hot, but the last one while
in the process of kicking the bucket is the killer.

- Don Klipstein )