We came out today due to circuit #24 which is on a AFCI breaker tripping. The customer stated that the breaker would not stay on even when everything was unplugged. The circuit controls the two bedrooms, the left bedroom has (5) receptacles, (1) single pole switch for a ceiling fan and right bedroom has (5) receptacles and (1) single pole switch for a over head light. These two rooms have a 12g NM-B cable feeding the rooms and is on a 20 amp breaker. We started with a diagnostic and only found one area in the left bedroom where the insulation on the black and white wire where damaged and exposing the copper conductor. We turned the breaker on and turned the lights on with no tripping. I made the homeowner aware that due to the breaker on and holding it is very difficult to find the issue. For a piece of mind we replaced the breaker, corrected the damaged wire. I went into the crawl space to see if any wires were damaged or to see if any illegal wire had been done. The only thing that I