I talked to a PG&E lineman. He said that it was a kind of breaker intended to shut down power in case of a detected short in the system (like a breaker in your house). He said that as a result of the recent court rulings (actually he blamed the Governer who has no say in the matter), PGE was forced to set these breakers at their highest sensitivity and that the excess power consumption due to the Holiday influx of people had caused the breakers to trip. Once tripped, PGE has also been ordered to do a 100% physical inspection of all the lines in the effected area and this is what takes most of the time.