On Sat, 12 Dec 2015 12:37:50 -0500, wrote:

On Sat, 12 Dec 2015 10:25:30 -0600, Muggles
wrote:

On 12/12/2015 3:11 AM, Don Y wrote:
On 12/4/2015 1:43 PM, wrote:
On Fri, 04 Dec 2015 13:12:26 -0700, Don Y
wrote:

On 12/4/2015 8:28 AM, wrote:

But, that will wait until at least the weekend. I have many other
things that need to get done in the short term and the forecast
suggests
I've got at least a week before temperatures begin to approach the
lows that are troublesome...

You can't get more "structured" that just plugging a comparable load
into the receptacle that fails (without involving extension cords tree
lights etc)

What if the nature of the load has an impact on the results?
E.g., say I plug a large power supply for that has an insane
turn-on transient in but idles at just a few watts (switching
losses). Smaller load but bigger turn on transient.

Or, drag out a longer spool of wire to use as the extension cord?

Or, try the toaster oven on one and lights on another?

Don't add variables to the analysis. Just come up with a
consistent test strategy and apply it consistently.

E.g., the second set of 3 strings that I dragged out to
mimic an "equivalent load" (as the first set that are
presently IN the tree) is only conceptually an identical
load. Making observations with one set in one case and
another set in another case isn't apples-apples.
Even though it might (and quite probably is!) appear to
be so.

For the purposes if this discussion, a hair dryer would do just fine.
If it trips, you know you have a problem in the wall or receptacle
string. Then try it at the end of the extension cord. If still no
trip, there is a problem with your lights.

You've not been paying attention to the numerous "experiments"
I've already conducted.

E.g., different extension cord -- trips. Different light strings (same
cord) -- trips. Different GFCI breaker (same branch circuit) same
extension cord, same lights -- trips. "Cold" lights -- trips.
"Warm" lights -- no trip.

Extension + cold lights plugged into non-GFCI branch circuit -- *no* trip.
Ditto for different GFCI branch circuit, no trip.

I.e., nothing wrong with extension cord *or* lights.

Toaster oven (reported by SWMBO) plugged into same outlet WITHOUT extension
cord -- trips.

Problem is *clearly* with the wiring in the wall -- the only thing common
to all fault cases and NOT present in any of the non-fault cases! And,
only manifests when a load is present. Furthermore, only when the load is
significant ("cold" lamp strings)

The idea that an incandescent light will trip a GFCI in normal
operation (no faults) is ludicrous.

The whole point of the discussion is that there *is* a fault!
Note that a much larger load (3X) had been present on the same branch
circuit last Winter with *no* problems for the entire season!

That tiny surge while the filament
is heating up is well inside the trip curve of any breaker I have ever
seen. It would certainly be less than the heat up time of a hair dryer
element.

Forecast was for a cold night, tonight. So, rushed to get *something*
working -- regardless of an "explanation" -- in the hour I had before
sunset.

As it was obvious that the problem had to be in the branch circuit,
I removed all receptacles, examined the routing of the conductors
within each Jbox, inspected all wire nuts, screw terminals, grounds,
etc. and, then, reassembled everything. Washed the "wet use" covers
just to make things look pretty (continuous sun exposure turns the
exterior paint to a powdery substance).

No "obvious" problems: no "bugs" falling out of the receptacles, no
corrosion on terminals, no exposed wires under wire nut skirts, no
nicks in insulation, no moisture in boxes, no mounting screws pressing
on conductors, no cables pinched in clamps, plenty of room in each box
(35 cu in), etc.

Circuit has been holding without any problem -- even in the (unexpected!)
rain that's been falling (and the "false alarm" for the cold weather!).
Added another 2 strands of lights (with a second extension cord) just
to push my luck...

Took the (inexpensive -- $1) precaution of fitting "child proof" plugs to
all unused outlets to ensure nothing *can* crawl into any of the outlets
in the future.

No way to ensure I can recreate the problem -- as I have no idea
what it *actually* was -- so I'll leave well enough alone and wait
for the next hiccup. Maybe buy some 20A receptacles to replace
these when I next have to go poking around in the Jboxes...

Case closed.

Perhaps something wasn't plugged all the way in and you fixed it when
you checked everything?

More likely that there was a neutral fault that was cleared when he
pulled everything apart and put it back.
Lots of mystery GFCI problems are fixed by an inspection that didn't
actually find a problem. Who knows what it was?
"It's all in the way you hold your mouth"