So I needed extra circuits to wire a kitchen reno. There was an existing small sub panel (60A feed from main) which was full so I replaced it with a brand new homeline sub panel with plenty of circuit space. There are 2 other CAFI breakers in the sub with no issues. I wired some general use wall receptacles which, as per code, were protected by a combination arcfault breaker. This circuit also has a ceiling fan wired on it (with wall switch) but the fan didn't get installed until they bought the darn thing about a month later. Before the fan was bought, I energized the plugs (and the maretted fan circuit), tested them all and everything worked fine...no tripping. A month later I wired the fan in and fired that puppy up. Fan and fan lights worked well for about 30 minutes, until the homeowner came home and wanted to pull the pull chains on his new fan. He operated the fan and then the CAFI tripped. Naturally, I assumed a bond was touching the Neutral somewhere so I checked and it was not the case. I disconnected the first plug from the feed and confirmed the feed was good as the breaker held. Connected the feed again and opened the fan switch box. With the fan switch extended out of the box, the CAFI reset and held...I pushed it back in live expecting the breaker to possibly trip but it did not. It stayed working for a whole day then tripped again. Went back, took the hot leg off the fan wall switch and the circuit still tripped. I then took every plug out again and checked the feed again....This time, with not a single thing connected to the feed (Hot and Neutral both disconnected, just a open ended 14/2 connected only at one end to the CAFI... it still tripped. Put in a normal breaker and she held. Put a SECOND brand new CAFI breaker in and it tripped immediately...so likely not a bunk ARCFAULT breaker. Last ditch effort, installed a normal breaker and fed and ARCFAULT receptacle at the panel. Then put every single device back in the circuit one at a time, energizing the circuit each time to verify. Lastly, slapped the fan back in the mix and everything worked fine. Circuit has been fine for 2 days now. Any ideas? Comments? Advice? This one bothered me as there was no culprit found. Also, anyone know of any specific diagnostic tools that would be useful in one of these predicaments? Sorry for the novel.