"James Sweet" wrote in message
news:bhcyh.1762$177.111@trndny08...
Ok on that, both replies. Makes more sense now if I'm understanding it
right. Less volts, more current, so thermal series trip opens - right ?
Yep, I'm in the UK. Mostly choke ballasts with PFC cap on the older
fittings, but some newer ones are starter-less, with no PFC cap. I'd
never really taken that much notice. I have a mixture of both between the
house and two lots of business premises, and I just replace the tubes
with whatever comes to hand at the time from the supermarket or wherever,
and have not had a problem so far - fingers crossed ;~}On the PFC cap, I
seem to remember years ago that it was a big thing to disconnect it.
Stopped the fittings registering on the electricity consumption meter due
to the big phase angle between volts and amps caused by the choke ??
Yep, our autotransformer fluorescent ballasts are thermally protected,
it's an automatic resetting thing wired in series with the primary
winding. The problem with this is once the ballast starts to fail and
overheats, it will start cycling and most people have no clue what's going
on and ignore it. Sooner or later the protector contacts weld together and
then if you're lucky, the ballast heats the fixture body enough that the
supply wiring melts, shorts out and trips the circuit breaker. Not
everyone is lucky, as it's not unheard of for houses or commercial
buildings to burn down due to faulty ballasts. Usually it's a fluorescent
light that gets left on all the time. It's not very common but it has
happened.
Disconnecting the PFC cap should make the fixture read higher on a UK
electric meter. I just found out fairly recently that they measure
apparent power rather than true power. On a US style meter, the PFC makes
no difference on the reading, but low power factor equipment makes the
power company happy. Not sure what explains the difference in meters,
cultural perhaps? Either way, the only sensible reason I can think of to
remove the PFC cap, if it can be called sensible, is the installation of
older tech fluorescent dimming systems.
Just as an aside on the subject, I was looking for some shatter-proof
types ( which I've since found out that they all are now, apparently ?? )
to go in a food prep area, and I found out where the " T12 " or " T8 "
thing comes from. It would seem that for some archaic reason, the
diameter of the tubes is quoted in eighths of an inch, so a T8 is one
inch diam, a T12 is one and a half inches, a T2 is a quarter inch and so
on. Just goes to show, you're never too old to learn ... !
It's not just fluorescent tubes, other bulbs are in T, BT, PS, R and other
envelopes using the same measuring system. There's a page in an old sales
book I have at http://sparcbox.hopto.org/files/GE%20HID%20Lamps.pdf which
shows all the different envelopes as well as has lots of other cool
lighting information. Do copy it down locally before you try to view it
though or you may see errors.
To make things more complex, our T8 tubes and your T8 tubes are not the
same. The T12s I believe are, at least the conventional type. 4' tube is
40 watts, rated 430mA, I have here a Thorn EMI ballast from the UK which
runs one of my tubes just fine using a 240V supply. The T8 tubes on the
other hand are 32W here, and are rated to run at 230mA from a high
frequency electronic ballast. The only magnetic ballast T8s we ever got
are either 18" or less in length and used with chokes, or the rare single
pin end instant start T8s, but most single pin lamps are T12.
Thanks for that James. As I said, not really my field, but one I have an
interest in, so this is all fascinating stuff. I visit the U.S. a couple of
times a year, and have never even begun to suspect that there is any
difference between our flourescent fittings, and the ones I see over there.
Just goes to show ... ! As far as I know, here the " T " number just refers
to the physical diameter of the tube, and has no bearing on the power
rating. Although I have just been and looked at a few around the house, and
all my 5 foot T12's seem to be rated at 65 / 80 watts, and a 5 foot T8 that
I have, waiting to be disposed of, says 58 watts on it. The 6 foot T8's in
my garage say 70 watts on them !! So now I'm not so sure. I must admit that
I have never really taken any notice, and have had both T8's and 12's in all
of the fittings over the years, without any apparent problems. They seem to
be sold over here as either 'standard' or 'slimline' tubes, with no
indicated electrical preference for any particular age or type of fitting,
and no special reference to the power rating. If I went in an electrical
shop and just said " A 5 foot flourescent tube please mate ", the only
question I would then get asked is " Standard, or slimline ? " Personally, I
prefer the standard fat ones. It's probably just psychological, but I always
feel that the much larger surface area, gives out a stronger more 'even'
light.
Interesting also about PFC and the meter, and the differences between UK and
U.S. metering of supply. I thought a watt-hour meter was just a watt-hour
meter. I wonder watt ( !! ) the difference is in measuring technique between
a " true " one and an " apparent " one, and which overall, gives the more
accurate long-term consumption figure ? Could this be anything to do with
PFC caps and flourescent fixtures not reading on the meter? This
disconnecting of the cap was definitely a big thing years ago here, and I'm
pretty sure that it wasn't the stuff of urban myth. I know for sure that
when I was a teenager, and had a room that I used for all my radio gear, I
had the cap disconnected in the fitting in that room. I am sure that I had
shut everything in the house off ( it was a lot easier to do that back then
!! ) and proved that the light no longer caused the meter to go round. I
will have to look into this further.
Sorry everyone for taking this a bit OT.
Arfa