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ground fault in undeground cable

1210 Views 4 Replies 4 Participants Last post by  dmxtothemax
We have a 12-2 UF cable going underground 20 feet to a driveway lamp post. After some spring flower digging was done in the yard, the GFCI breaker for the circuit began tripping. I isolated the underground wire by disconnecting the white and black wires at the lamp post and also in the junction box in the crawl space where the UF feeder wire exits the house. A multimeter gave a continuity reading of about 60 K-ohm from black to the ground wire and white to ground, which I assume indicates a ground fault. I dug down to the UF wire where the yard digging had taken place, and a section of wire was found to have several significant nicks. I cut out that section of wire. At that point I expected there to be zero continuity in the remaining underground wire going back to the house. However, now the reading from black to ground and white to ground is 11 M-ohm. There is zero continuity from white to black. My question: Is this amount of continuity to ground negligible and/or acceptable and/or to be expected in an underground situation? Or does it indicate another ground fault problem elsewhere in the remaining 19’ of underground wire that must be corrected, i.e., a small ground fault that might not be enough to trip the breaker but still leaks current to ground. Many thanks for your assistance with this perplexing question.


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I don't have a direct answer, but the old spec for PVC was a minimum of 2000 K Ohms (2 Megaohms) ICEA-NEMA Standards 5-61-402 WC-5. All the specs were replaced with new ones a few years ago. I believe the one that replace the one above is ANSI/ICEA S-95-658 / NEMA WC70 Nonshielded 0-2kV Cables

NEMA want you to pay a minimum of your first born to see inside their documents. Maybe someone here can can show the information.

The only online reference I can find is 8 Insulation and Related Cable Components.pdf

BTW The testing is done with what is called a Megger which applies low current high voltage and measures the resistance. The key being the high voltage.
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