On 12/16/2012 9:11 PM, DerbyDad03 wrote:
I bought a few sets of Philips mini Christmas lights this morning. As I was
putting them on the tree, I noticed something about the plugs and sockets.

1: The plug does not have a wide neutral prong.
2: The socket on the back of the plug will not accept a wide neutral plug
because there is no wide neutral slot.
3: The socket at the end of the string *will* accept a wide neutral plug
since it has a wide neutral slot.

I wonder why that it is. Yes, it allows me to string together lights from
other manufacturers that use a wide neutral plug, but there is no guarantee
that the neutral is actually connected to the neutral because the Philips
plug doesn't force the user to orientate the plug in any given manner.

Why not build the plug and socket at the start of the string with a wide
neutral prong and slot or build the socket at the end without one? Why mix
and match?

I've read all these replies, but I really think I have an answer. I too
have always wondered, but for me I've wondered why are these things
polarized. I think I have an answer. On older light strings, with a
non polar plug, they usually have 2 fuses in the plug so if the plug it
put into the socket in either way, the hot will have a fuse. In
essence, because the lights in the strings are wired in series, the 2
fuses are also in series. But the safety aspect is that if something
shorts to earth ground in the beginning of the string, it should take
out the fuse that's on the hot side, whichever way it is plugged in.
BTW, the second reason for the fusing itself is that in each bulb there
is a shunt which 'activates' when the bulb's filament burns out (opens),
thus keeping the circuit complete and keeping the remaining lamps lit
(if the shunt actually works!). If multiple bulbs in the string burn
out, you can get to a runaway situation where more and more current
flow, burning out more and more lamps until all that is left is shunts.
The fuse(s) protect against the large currents causing bad things to
happen with the bulbs and/or wiring. But, of course, for this case only
one fuse is needed. So, to save on putting in the 2nd very cheap fuse,
they only put one fuse on the hot side and use polar plug to guarantee
it. BTW, some older strings had 2 special bulbs, which were called
'fuse bulbs' which apparently didn't have shunts and usually had some
green paint on the bulb. They usually had a different base, so a
regular lamp could not be plugged in these special sockets. But these
seem to have disappeared through the years. So now, we seem to be
stuck with this polar stuff. A small file or a moto tool works wonders,
but I always make sure they are plugged in the 'right' way .... yeah sure