Thanks Bill. I've taken apart (2) 3-gang, (1) 2-gang switch box and a receptacle JB in order to find this problem. I narrowed it down to the 3-wire NM cable between both 3-way switches which led me to believe it's either an over-driven staple or possibly a sheet-rock screw that hit the cable. I did not take the recessed lights down. There was no EGC-N short in that wiring. The wiring that I could see exposed in the basement and the wiring to the new MBP was done neatly and with extreme care. I want to believe this was an inadvertent problem caused by a staple or a sheet-rock screw. It could have happened to any one of us and not necessarily a hack or an apprentice IMHO. Thanks for the reply and your insight.
It's hard to believe that this renovation was done without permits but I found no inspection sticker on the MBP for the renovation or the service upgrade. So, I asked the HO to make an inquiry to the bldg dept. to find out why. At that point he will find out who the EC was and he can pursue it further if he wishes to.
Do you mind sharing what instrument is telling you this ?
For the entire circuit I initially used an Ohm meter. Once I established there was an EGC-N short I removed the circuit wiring in the breaker panel and used a "sounding" continuity tester that I made up years ago (everyone laughs at me when I make up my own stuff - like test equipment). That way I didn't have to keep going into the basement each time I split apart wiring. I narrowed it down to the 3-wire between the two 3-way switches and went no further. Once I remedied that situation, I put all the wiring back together in the JB's and re-connected the AFCI breaker.
I have about two-three arc faults that will trip every time we get a bad storm.
I've been there when they tripped when POCO had a cycling of a recloser as well. Maybe back in about 2010 or so, but was in new house we were still working in. Power "blinked" which is not totally uncommon on rural systems, reclosers operate occasionally for many reasons when you have a system that covers such large area in the open wilderness. Several AFCI's in that house tripped at that time but not all of them. The ones that did trip was mostly ones that had active lighting loads at the time so I assumed loading had something to do with them tripping and maybe a transient voltage on the line was another factor?
FIFY
Did one like that this morning. Defective power strip would not have been found with a continuity meter.
A good description of a megger test is the one required for RV's in 551.60
Did you not take note that I said after unhooking the cables from the 3 way and then test? Precisely because of the Led light.
Dwellings with cloth or rubber Type R insulation were made well into the 1960's, and never rated over 60 deg.C, much less for modern hi-pot testing per NEC 551.60.
Except for European standards for insulation tests during domestic commissioning @ 500+ V for their 220 V systems (United Kingdom BS7671-2008 Appendix 13) US regulatory bodies may only defer to OEM instructions for proper application of tools & equipment. The Supco500 does include appliances among its undocumented list of applications, however, unclear if that is 240v and 120v appliances.
Standard breakers & fuses tolerate low level faults that will often trip an AFCI, GFCI, or Dual Function device.
