Capacitive coupling and gfci

[domnic]

HYPOTHETICAL QUESTION, IF HAVE SAY 300 FT OF ROMEX 12-2 WG, AND I HAVE 300 FT 12-2 NO EGC, AT THE END OF EACH RUN I HAVE A GFCI, CAPACITIVE COUPLING CAN MAKE THE GFCI TRIP WITH THE EGC, BUT NOT THE ONE WITH NO EGC . ????????????????????????????????????????????????????????????

 

[junkhound]

see the UF thread
wg has about 10 nF per 250 ft, no EGC negligible path for leakage current if against wood in air.

higher if buried, on concrete, or grounded metal. Either way, unburied against wood not enough to trip.

 

[jim dungar]

If the GFCI is at the end of the run, as per the OP, the amount of capacitive coupling on its line side should not be an issue.

 

[domnic]

see the UF thread
wg has about 10 nF per 250 ft, no EGC negligible path for leakage current if against wood in air.

higher if buried, on concrete, or grounded metal. Either way, unburied against wood not enough to trip.

GFCI at start of run. sorry.

 

[synchro]

It's very unlikely that the capacitance of 300 ft. of Romex (with or without an EGC) would cause a GFCI to trip. See the responses to your earlier post:
https://forums.mikeholt.com/threads/gfci-tripping-on-200-run-of-wire.2563675/

 

[Jraef]

Some GFCI mfrs state a maximum circuit length. IIRC, Square D says 250ft.

Some references:

What is the maximum total length of load wire that can be used with a QO-GFI or QO-EPD circuit breaker? | Schneider Electric USA

Length of conductor on GFCI breaker

I read a note in the SQ D digest that said we should not run the conductors fed from a GFCI breaker longer than 250' (one way) to avoid nuisance tripping. Has anyone dealt with this? Have you had a problem in the past? The reason I'm asking, I'm looking at ways to comply with 555.3, and one...

forums.mikeholt.com

Understanding GFCI Nuisances | Henderson Engineers

Since the expansion of the 2017 National Electrical Code (NEC) ground fault circuit interrupter (GFCI) requirements to include single-phase receptacles up to 50A and three-phase receptacles up to 100A, we’ve seen a trend of increased ...

www.hendersonengineers.com

 

[synchro]

Some GFCI mfrs state a maximum circuit length. IIRC, Square D says 250ft.

Perhaps this is because a 250 ft. length would not be enough to cause it to trip by itself, but it would begin to reduce the amount of leakage current required for it to trip (say by some noticeable amount such as 10%). But it would take a 2500 ft. length that had 35.4 pF / ft. to cause 4 mA of leakage at 60 Hz, which then could trip a GFCI by itself.