On Thursday, December 3, 2015 at 12:01:30 PM UTC-5, 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


The GFCI isn't putting gradual force on the breaker to open it. It's
detecting when a fault current exceeds the ~6ma level and driving a
solenoid that opens the breaker. It's an all or nothing, instantaneous,
thing, not gradual.