From: "Chuck Guzis" <cclist at sydex.com> Subject: Re: New DEC museum entry :D <snip> As mentioned by several others, GF(C)Is detect an imbalance between hot and neutral and do not in fact care about ground at all. Since the neutral is normally bonded to ground at the main panel, it would require considerable current in the neutral to generate a detectable voltage difference between neutral and ground at the receptacle; in the unlikely event that the neutral is not at ground potential a GFCI would still trip on a fault. In fact, if you have to replace one of the unobtainium 2-prong ungrounded receptacles in an old house wired with knob & tube (or the '50s era 2-wire NM non-metallic sheathed), replacing it with a GFCI receptacle will give protection similar to a grounded outlet (although of course running a ground wire back to the panel is preferable, since an internal short or leakage will not be detected until there is an external path to ground, and noise suppression filters will be ineffective). The "bedroom GFCI"s that Ethan mentioned are actually Arc-fault interrrupters, required by most jurisdictions for the last 4 or 5 years in bedroom circuits because neither a circuit breaker nor a GFCI will trip on an arcing short or connection (the cause of many if not most residential electrical fires) if the current is less than the breaker rating. mike