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Don Y[_3_]

On 12/2/2015 12:57 PM, wrote:
On Wednesday, December 2, 2015 at 2:07:56 PM UTC-5, Don Y wrote:
On 12/2/2015 11:54 AM, dpb wrote:
On 12/02/2015 12:08 PM, Don Y wrote: ....

This can't be the problem. Lights have been on all night. "Unplugged"
them (i.e., don't muck with the breaker).

Wait *1* second and plug in, again. Lights come back on (i.e., breaker
does not trip).

After a few seconds, unplug again. Wait 10 seconds and plug back in.
Again, lights come on.

After a few seconds, unplug a third time. Wait 2 *minutes* and plug
back in. Breaker immediately trips.

That's got to be a thermal problem in (probably) a particular
lamp...eventually it'll burn out and let you isolate it or the base
itself will fail.

Unplug the three strings from the extension cord. Leave cord exactly as
is. Take three *other* "identical" strings out and wire them in exactly
the same fashion as the first set-of-three.

Turn on breaker. Trips immediately. Let it reset and turn it on a second
time. Holds.

Walk around house to return to the point where the extension cord is
plugged in.

Unplug. Wait a few seconds. Plug back in. Breaker trips.

(No, I'm not going to keep repeating this test to see how long it takes
for the load to "deteriorate" between power applications. The fact that it
tripped suggests the problem is not in the original three strings of
lights -- or, coincidentally ALSO happens to be in the OTHER three
strings, as well. And, no, I'm not going to drag out a third set of
three... or a fourth set of three... : )

Seems that the surge current of all those bulbs is just a bit too high for
the breaker.

In the past, there were 3 times as many bulbs in place without a problem!

So here's a question...

I assume the lights in question are small incandescent bulbs.

IIRC, they are 9W, miniature base.

Are they the type that you can unscrew one and all the other bulbs stay lit
(indicating they are wired in parallel) or are they the tiny bulbs that if
you unplug one bulb many others in the string go out as well (indicating
that they are wired in series)?

The bulbs are wired in parallel. I.e., the two conductors pass *to*
each socket and continue onward to the end of the string. At that
point, an outlet is located -- which feeds the next string in the
"series" (as in "sequence").

The wire gauge is such that you aren't supposed to daisy-chain
more than two additional strings onto any string in the "series".
Hence the reason we use a cube tap to start a new "set".

Running each string to a single feed point (from the extension
cord) greatly complicates the logistics of getting lamps all the
way around the tree. And, makes the end of the extension cord
a crowded place...