Redsy,
Just a little trivia here. We had a rep from UL at a meeting last week and GFCI's was the main topic. (This was also in the Theory section)
GFCI protection for personnel is set to trip between 4ma and 6ma. An interesting thing mentioned was that the speed with which they operate depends upon the level of the fault. A low threshold 4ma fault could take up to something like 4.8 seconds to trip depending upon the sensitivity of the particular unit.
Another piece of trivia. An Electrical product is permitted to have a loss up to .5ma and still be listed. The importance of this tidbit comes into play where there is a 'nusance' tripping going on. As the GFCI operates on a cumulative value of stray current it could seem to be tripping for no reason but it may be operating perfectly. There could be 8 items on the circuit with a .5 'loss' each (8 x .5 = 4ma) and tripping could occur and there is nothing wrong. It's something to think about when deciding on CB vs Receptacle type GFCIs' and the number of downstream devices and length of a circuit protected by a single GFCI.
That's a good point to bring up because it is very common (around here anyway) to see a single GFCI protecting all the Bathroom, Basement, Garage and outdoor receptacles. (3 different levels) Most times it'll be fine (except for the Hairdryer and the dehumidifier in the basement on the same circuit that is) There is a distinct possibility that a GFCI towards the sensitive (4ma) trip rating might be nuisance tripping in a situation like this and replacing with another (possibly less sensitive) may solve the problem.
Sometimes I've noticed some inexplicable tripping going on especially where there are GFCIs feeding each other. Removing one seemed to solve the problem.
Bill
