I've got a breaker that keeps popping. The 15-amp circuit in the basement consists of several light fixtures and outlets. None of the outlets have devices plugged in, and I don't think any outlets are controlled by switches. There's a set of switches for a bathroom (call it A), a set of 2 3-way switches for fixtures on the stairs (call it B), and a switch for 2 more fixtures (call it C). With everything turned off, the breaker does not trip immediately when resetting it. It takes a combo of at least any 2 of switching A, B, and C on to cause it to trip. Usually it trips immediately after turning on the second switch, but sometimes it can take 5-10 minutes. Early on, I tested the breaker and it read 120V. I have replaced all switches B and C. Switches on A read at 120 V. Fixtures on B and C read 120 V in each socket. All the outlets are fine (grounding included) with testing via neon tester. It seems like a question of wattage load but we're not anywhere near 1800W. Could the breaker have gone bad since I tested it, considering the countless times I've tripped it trying to troubleshoot it?