On Wed, 02 Dec 2015 03:35:57 -0600, wrote:

On Tue, 01 Dec 2015 19:19:01 -0700, Don Y
wrote:

The outlets in the back of the house are on a 20A GFCI.
(Note to self: are there any other outlets on that same
circuit that I need to chase down?)

Presently using them to light XMAS lights on one of the
citrus trees. IIRC, each string is about 250W. With
~700W on the circuit, turning the breaker ON (i.e., using
it as a switch -- instead of plugging/unplugging the
load) causes it to immediately trip. Repeating the
action in short order appears to get it to latch and
remain latched (ON), indefinitely.


What are yiou using for lights? It sounds like they are incandescent C9
bulbs in strings of 25 bulbs. (which is actually 225Watts). [25 times
9watts].

OK, so the surge when all the lamps are cold can increase
the inrush current -- on the short term -- to levels that
probably exceed the 20A limit of the breaker.


700W is not even close to 20A.
A 20A breaker can handle roughly 2400 watts.
(Of course you dont want to run it at it's maximum load).
Either way, 700W is only around 30% of the capacity of the breaker.
Yea, starting current is always higher, but even if it was double (1400)
watts, you're still way below the allowable load limit for a 20A
circuit.

"In theory"

OTOH, in years past, I've run the circuit at close to its
capacity (~10 strings) without this problem.

I've changed breakers (swapped with one feeding another
circuit) and the problem persists.

[There are no leakage paths in the wiring OUTSIDE]

This suggests something in the wiring/fixtures. I'll
start isolating outlets, tomorrow (dark here, now).
Perhaps some insect (leaf cutter?) has opted to nest
in one of the receptacles.

Anything else I should explore?

Check, check twice, check 3 times and check again for any minor breaks
in the light strings. One very tiny spot of bare wire, a bulb base
slightly exposed and touching a tree branch, or the soil, and so on....
Christmas light strings are notorious for electrical leakage and if
they're old, even more so.

Also, years ago, when I used to decorate outside of my parents house,
using those C9 (and C7) strings, more than once one of the bulbs seemed
to develop an internal short. Apparently the filament broke, but welded
itself back together but it was shorter and drew excess current. That
bulb would eventually burn out, but sometimes it would blow a fuse when
it died.

So, you might check every bulb for any sign of defect, which is easier
said than done. Or replace all the bulbs in one string at a time.

Better yet, just buy some C9 sized LED strings, and if you have them on
every night until the end of December, they will probably pay for
themselves in electrical savings. Just a guess, but a string of 25 LEDs
probably use about 20 to 30 watts.

Three strings of incandescent will use 675W (Roughly 700W) every hour.
So whatever you pay per KWH, is spent approximately every 1-1/2 hours.

As an example, if you pay 15 cents per KWH, Six hours per day will cost
you 60 cents per night. That's a cost of $18 for one month.

Three LED strings will use around 80W per hour. 480W in 6 hours, which
amounts to about 7 cents per day or $2.10 for an entire month.

You save $15.90 in that month.

But the current spike on LEDs can be pretty healthy too- depending
what kind of driver circuit. Just a series string, not so much - but
LED drivers? OUCH!!