On 12/2/2015 12:31 PM, dpb wrote:
On 12/02/2015 1:08 PM, Don Y wrote:
On 12/2/2015 11:54 AM, dpb wrote:
....

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.

....

Hadn't seen the duplicated test result...

I'd stick with the thermal issue and I'd suspect the cord if it's one of those
w/ the indicator lamp built into the plug.

Did you ever isolate whether there were any other loads on this circuit besides
these two (I think were mentioned early on?) exterior receptacles?

The only (intentional!) load on the circuit is these (or "those" -- depending
on whether you refer to the original 3 or the replacement 3) 3 strings of
lamps.

I.e., in a theoretical scheme, it's just a long wire with a bunch (5)
of duplex receptacles hanging off it, fed through a circuit breaker
(which has been replaced with an "unused" GFCI).

The fact that the different strings don't appear to make any difference
to the result *suggests* it's not in the "load".

The fact that a different GFCI doesn't appear to make a difference
tends to rule that out.

This leaves outlets, wiring and extension cord.

The fact that lights plugged into extension cord doesn't cause a
problem on another branch circuit suggests the cord MIGHT not be
a problem (it could still be "leaky" and the non-GFCI doesn't
notice that).

I can remove receptacles from the wiring (a bit of a hassle to
remove the "outdoor" covers, remove the receptacle, then
remove the two conductors -- I can leave the safety ground as
long as I ensure the receptacle is "dangling freely")

Isolating portions of the wiring gets to be a bit more
involved; instead of "daisy chaining" through the second
set of contacts on the receptacles, I tie the upstream and
downstream wiring together with wire nuts and run a pigtail
off to the receptacle. This ensures the receptacle is not
"in series" with the downstream devices.

But, today is shopping day. frown So, instead of using the
daylight hours to troubleshoot the problem, I'll waste them
running around buying "stuff". (sigh)