On Thu, 3 Dec 2015 09:01:23 -0800 (PST), wrote:

On Thursday, December 3, 2015 at 9:17:11 AM UTC-5, trader_4 wrote:
On Thursday, December 3, 2015 at 9:04:11 AM UTC-5, 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.

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 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)


Yes, they are separate. The fault current is measured by comparing the
balance between the current in the hot and neutral and it trips
independently of the overall current. Adding wouldn't get you anywhere
because the fault current trip is three orders of magnitude smaller than
the load current trip.


Of course the currents are not added directly.
That is not what i meant.
5 mA is nothing compared to 20A.


I mean the trip forces in the mechanism might add.

If 19 Amps puts say 1 pound of force on the trip mechanism and 3 mA also puts one pound of force, then each alone might not trip it, but together they put 2 pounds of force which could be enough to trip it.

These are mechanical devices afterall.

Mark




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.


I agree that cold bulbs will draw a lot more current initially.


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.

Mark

I thought he said he had done that and it worked without tripping?
On the Square D the 2 trip mechanisms are totally separate, and the
GFCI load section is the same as the non GFCI breaker. No idea what
breakers you have in the CH panel, but "generally" that is how they
are made.