How can you tell if a breaker is good or not? What you don't want to do is "test by tripping." That method merely proves the breaker can be opened — it does not prove that the breaker will automatically open or will do so at the correct setting. Doing this with loads on the breaker is extremely unsafe once you get beyond the small branch circuit breakers. Before opening a breaker, remove the loads by opening all downstream breakers (using lockout/tagout).
The process of verifying if a breaker is good consists of many tasks. The first task is to remove the loads and take it out of service. Using your DMM, verify that this breaker is de-energized. Now you're ready for the next step, which is a visual and mechanical inspection. We'll look at this in our next issue.