AFCI nuisance tripping is the most common callback complaint in residential right now. The short answer: most nuisance trips are caused by either (1) wiring issues that the AFCI is correctly detecting, (2) incompatible loads on the circuit, or (3) a bad breaker. The trick is figuring out which one you’re dealing with without spending three hours chasing ghosts.
Start by isolating the circuit. Kill everything on it. If it still trips under load, you’re looking at a wiring problem - likely a parallel arc somewhere in the run, a nick in the insulation, or a loose connection that’s arcing under current draw. If it trips only with certain loads (LED dimmers, motors, some older electronics), that’s the load causing a waveform that the AFCI interprets as an arc.
The NEC (2020 and 2023, Article 210.12) requires AFCI protection on ALL 120V 15A and 20A circuits in dwelling units. That includes circuits added or modified - so any time you pull a permit for a remodel, you’re potentially on the hook for upgrading existing circuits too. Some AHJs are enforcing this more aggressively than others. Know your local adoption before you’re standing in front of an inspector.