gfci tripping on 200' run of wire

[synchro]

z = 240v/4mA = 60k; 4 mA low limit of GFI
= 1/(377*C)
C= 44,000 pF ; (0.044uF)
44k/250 ft = 176 PF per foot for UF 10/3 ???? (to lazy to go to the shop with capacitance meter this late/early and measure a roll<G>)

Unless I dropped a zero, methink the tripping NOT due to capacitive current - Unless there are a LOT of higher frequency harmonics.

A GFCI will trip on the difference of the L-G leakage currents on the two conductors, and this would be the current through the excess amount of L-G capacitance on one side when 120V is applied across it. And so to produce the 4 mA low limit trip current, 0.089uF more L-G capacitance on one side than the other would be required. In other words this would be the minimum amount of unbalanced L-G capacitance on the two conductors before a trip could possibly occur. I agree that the capacitance per foot required for this seems too high, especially since we are talking about the amount of unbalanced capacitance and not the L-G capacitance itself.

To make sure there are no other factors involved I did some testing. I applied a fault current from line to ground on the output of a 120V GFCI receptacle using various capacitors.
As I increased the capacitance it started buzzing, but it still did not trip with 0.185uF which would draw 8.4 mA at 120V 60 Hz. It tripped when I reached 0.205uF which would be 9.3 mA of leakage at 120V 60 Hz.

 

[kwired]

A GFCI will trip on the difference of the L-G leakage currents on the two conductors, and this would be the current through the excess amount of L-G capacitance on one side when 120V is applied across it. And so to produce the 4 mA low limit trip current, 0.089uF more L-G capacitance on one side than the other would be required. In other words this would be the minimum amount of unbalanced L-G capacitance on the two conductors before a trip could possibly occur. I agree that the capacitance per foot required for this seems too high, especially since we are talking about the amount of unbalanced capacitance and not the L-G capacitance itself.

To make sure there are no other factors involved I did some testing. I applied a fault current from line to ground on the output of a 120V GFCI receptacle using various capacitors.
As I increased the capacitance it started buzzing, but it still did not trip with 0.185uF which would draw 8.4 mA at 120V 60 Hz. It tripped when I reached 0.205uF which would be 9.3 mA of leakage at 120V 60 Hz.

There is possibly some leakage in whatever the connected load is as well. Supply conductor maybe not enough to trip, load not enough to trip but the two together maybe is?

 

[junkhound]

A GFCI will trip on the difference of the L-G leakage currents on the two conductors, and this would be the current through the excess amount of L-G capacitance on one side when 120V is applied across it. And so to produce the 4 mA low limit trip current, 0.089uF more L-G capacitance on one side than the other would be required. In other words this would be the minimum amount of unbalanced L-G capacitance on the two conductors before a trip could possibly occur. I agree that the capacitance per foot required for this seems too high, especially since we are talking about the amount of unbalanced capacitance and not the L-G capacitance itself.

To make sure there are no other factors involved I did some testing. I applied a fault current from line to ground on the output of a 120V GFCI receptacle using various capacitors.
As I increased the capacitance it started buzzing, but it still did not trip with 0.185uF which would draw 8.4 mA at 120V 60 Hz. It tripped when I reached 0.205uF which would be 9.3 mA of leakage at 120V 60 Hz.

you are correct, I should have used 120V in the calculation vs. 240 V.

Even less likely cable capacitance alone is 'culprit'
Took meter to shop, no roll of 10-3 handy, but 12-2 NM is 7.5 nF (.0075uF) per 250 ft black to ground, 10-3 UF may be 50% higher if that, cable still a minor contributor.