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... : )