Re: Intermittent breaker tripping
Breakers do go out of calibration. I've had breakers trip randomly with no apparent overload or short circuit; replacing the breaker fixed the problem. I've also seen a breaker overheat (probably due a failing contact internally) and fail to trip.
If you've verified that the connections are good, that there is no apparent short circuit, and that you're not overloading the circuit, replacing the breaker is a fairly simple exercise.
The cost depends on the model of electrical panel. If it uses "current production" breakers, the cost of a replacement will be $3-10. If it's an obsolete panel, the cost could be as high as $50 (Pushmatic or Zinsco are horribly expensive).
Make sure you only use a breaker that's "listed" for your panel. The label inside the door should tell you what type of breaker can be used; usually it's a type-code of one to three letters. See the compatibility guide on this page -- ignore the "UBI" prefix (example: Zinsco is listed as "Type UBIZ" but it's generically known as "type Z".)
Another caveat: if you have a tandem breaker (two breakers in one housing without linked handles), bring the breaker in to the store and make sure the parts where it mounts to the panel are the same. There are subtle differences that can prevent a breaker from fitting.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.