| email@example.com writes:
|> It's that increasing current I was wondering about.
|> But you guys have actual fuses in your plugs. Why not set that fuse to
|> a bit above the proper current? Of course someone will end up replacing
|> the fuse with one of the wrong value.
| The plug fuse is for protection of the appliance flex only,
| not the appliance. If an appliance requires fusing in order
| to remain safe, it must include appropriate provision within
| itself. It is not permitted to rely on the plug fuse.
| Plug fuses go down to 2A in value, and that's still almost
| 500W which is plenty enough to ignite a christmas tree.
The string of Christmas tree lights isn't really an appliance. The ones
we have over here are basically the same wires coming out of the plug and
going all through the string. So there isn't any real boundary between
the flex cord and the rest of the string, unless you want to define that
as being the first bulb.
I remember some past light strings my family had. An older set of strings
my father got from his father was parallel wired with C7 bulbs. The plug
on these were strangely very flat and wide. You could easily plug several
outlets spaced very close together. They were non-polarized. But the
one interesting thing about these plugs is they were fused. You could
twist the prongs with a bit of force and release them and the prong and
fuse would come out. The prong actually connected directly to the fuse.
There was a small spring behind the fuse. But once the prong was twisted
in, it could not move either inward or outward. I do remember once my
father managed to have one come out while in the socket. Both prongs were
fused and neither were polarized (you could rotate the plug 180 degrees).
I'm sure the non-polarized aspect would be prohibited today, and the fuse
on the neutral might be as well (e.g. it's unsafe to have an apparently
dead, but hot, wiring).
We also had a series string with blinker lights. They blinked by means
of a thermal element that shorted the filament when it heated up. There
was what was called a "ballast bulb" at the head of the string. It was
a larger bulb with a different socket. It glowed a bit dimmer, but was
always going up and down in brightness as more or fewer blinkers shorted
out. There was no dead bulb bypass so if one bulb burned out the whole
string went dead. There were typically about 6 burn outs per season.
Today we have some non-blinker series strings with some kind of burnout
bypass. The bulbs have some very fine wire wrapped around the posts to
hold the filament. I suppose this is the bypass. These bulbs indicate
a 2.5 to 3.5 volt operating range.
OK, so let's assume 3 volts per bulb. You would have 80 bulbs for your
240 volts, and we would have 40 bulbs for out 120 volts. I think they
are about 1 watt each. I'd have to go dig them out early to see that
right now (should be doing that in about a month, anyway), as well as
count exactly how many are on a string. That would mean a current of
about 1/3 amp. So why not put a 1/2 amp fuse in the plug? It would be
better than say a 5 amp fuse just because the cord can handle 5 amps.
Then if too many bulbs burn out, and the current rises too high, the
fuse will blow. Or do they just not make 1/2 amp fuses in the size to
fit plugs? They should, at least for the light strings.
One thing I have found with these light strings is that about 30% of the
burnouts do not result in the bypass. Then I have to find the dead bulb.
The strings and lights are made in some small Asian Pacific Rim country.
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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