"James Sweet" wrote in message
news:hx9tb.200610$Fm2.189138@attbi_s04...

wrote in message
news:8H8tb.12766$f7.662436@localhost...
: I've never seen a fixture with a large electrolytic across the power
: line. Are you from the UK since you use the word "mains" for the
: power line? Any capacitor is probably just to filter out
: high-frequency noise from the lamp arc, 50 or 60 Hz and many, many
: harmonics. The capacitor is probably breaking down when exposed to
: the full line voltage, but not under the low voltage from the ohmmeter
: section of the multimeter. Almost any capacitor rated at twice the
: line voltage will reduce the "noise going back onto the power line.
: It is most evident when listening to AM radio. If you can use the
: radios in your house with the light on, without the capacitor, then it
: probably is ok to continue to use it without interfering with your
: neighbors radio reception. But if you are in an apartment house, you
: may cause interference to your neighbors radio due to the ac power
: lines radiating the noise.

: H. R. (Bob) Hofmann


The cap might be there for power factor correction. But on a single
fixture? I doubt it unless local code specifies so.
--

debaser at ecn.ab.ca
-@+.%

See this link
http://www.ambercaps.com/lighting/po...n_concepts.htm

Virtually all rapid start ballasts in north america have a power factor
correction cap, but it's traditionally sealed within the ballast casing.
These can be identified by the lable saying High Power Factor, next time
you're in a hardware store have a close look at a typical F40T12 rapid
start
magnetic ballast. In the UK the mains voltage is high enough that most
fluorescent fixtures use a simple choke ballast, it's more efficient than
the autotransformer ballasts we have here, but you need more than 120v to
reliably start tubes longer than about 2 feet. Choke ballasts here
generally
don't have a capacitor (never seen one that did) likely because small
tubes
are rarely used more than a few at a time.



I should add that older preheat ballasts had this as well, hence the reason
that they contained PCB's, which were used in the capacitor.