On Thu, 03 Dec 2015 15:00:23 -0700, Don Y
wrote:

On 12/3/2015 2:47 PM, wrote:
On Thu, 03 Dec 2015 09:45:28 -0700, Don Y
wrote:

On 12/3/2015 7:03 AM, wrote:

You do know that incandescent bulbs can pull about 10x the current on
turn on?

You do know that having 700W of incandescents on even a 15A circuit is
very common and doesn't cause breakers tripping?

OK...Lets talk details.

I don't know the details of the inards of GFI breakers. Maybe you do.

Lets say the COLD turn on surge is 20 Amps for a short time and that alone
is not enough to trip a 20 A breaker.

We know it isn't -- because I moved the extension cord to a non-GFCI circuit
and the circuit had no problem holding the load.

(We also know that in years past, a 15A-18A load had no problem on the
same GFCI circuit!)

Lets say there is also 3 mA of leakage and the trip point for the GFI
breaker is 5 mA so 3 mA alone is not enough to trip the breaker.

But what about both together? Maybe both together will trip.

I don't know. Clearly (?) there is something "GFCI-related" with the
current situation -- as a second GFCI breaker swapped in to replace the
original GFCI breaker is behaving exactly the same way.

I don't know if each trip point is totally seperate inside the breaker or
if they somehow are added. Do you? (I'm not trying to be snooty)

I don't. As I pointed out upthread, there's no guarantee that a
non-GFCI's current holding characteristics, response time, etc.
are the same as that of a GFCI breaker WITH THE GFCI PORTION DISABLED.

I do know that a truely COLD bulb turn on draws a bigger surge then one
where the bulbs have been pre warmed. It doesn't seem logical I agree, but
I have seen it. You have to wait a good number of seconds for the filament
to totally cool to get the full surge current.

Again, note the (apparently thermal) characteristics reported:
- breaker IMMEDIATELY trips when switched on with a "cold" load
(we'll leave the definition of "cold" vague, for now)
- seconds later, throwing the breaker holds, indefinitely
- "cold" lamps "plugged into" a live circuit immediately trip it
- lamps that have been on for hours can be unplugged and replugged
within 1 (or 10!) seconds and the circuit will hold
- lamps that have been allowed to "rest" for 2 minutes will immediately
trip the breaker

It sure *seems* like allowing things to "cool off" -- or, starting
with something "cold" -- is the differentiating aspect of the problem.

It doesn't seem like this small diffence should be the OPs problem but at
this point, who knows?

I agree with the suggestion to change to a non GFI breaker as a test to
eliminate the leakage part of the question.

Note that all this would do is isolate the "in wall wiring" as a potential
cause of an hypothesized GFCI issue. We've already tried a non-GFCI
branch circuit with the extension cord and lamps.

I'll try plugging the extension cord into a kitchen outlet (unloaded circuit)
as that would test a different GFCI with the existing extension cord
BUT DIFFERENT WIRING (as we've already tried a different GFCI with the
existing extension cord and THE SAME WIRING).

[This is easy to do whereas tying the existing wiring to a nonGFCI
breaker is a significant effort]
What GFCI breakers are you using in that "old ch" panel??

Are they listed for the panel? If it is an "old ch" panel the GFCIs
were not original install - correct? or is it not that "old" a CH
panel?

CH GFCI's for this particular panel. Did my homework when I
bought them. Hard to find cuz the panel is old -- can't just
walk into a Lowe's/Home Despot and pick them up!

Took advantage of a contractor friend's discount to buy them
from an (overpriced) electrical supply house, locally.

Lots of scrounging - lots of fun.