Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!decwrl!nsc!voder!blia!ted From: ted@blia.BLI.COM (Ted Marshall) Newsgroups: sci.electronics Subject: Re: How can I recognize true ground? Summary: GFCI outlet does not require a ground Message-ID: <8541@blia.BLI.COM> Date: 14 Jul 89 23:35:25 GMT References: <18425@mimsy.UUCP> <10040007@hprmokg.HP.COM> <29646@cci632.UUCP> Distribution: na Organization: Britton Lee, Los Gatos, CA Lines: 30 In article <29646@cci632.UUCP>, rdi@cci632.UUCP (Rick Inzero) writes: > A curious thing (before I discovered this ungrounded wire) is that when I > replaced the existing ordinary outlet with a new ground fault interrupt > outlet, it thought that there was a valid ground!! It functioned correctly > for about a year and a half (using the "test" button) ALTHOUGH NO ACTUAL, > TRUE GROUND WAS PRESENT!! Actually, a GFCI does not require any ground connection to operate. It works by comparing the current flow through the hot line with that through the nutral. If one is passing more current than the other, the button pops. The ground line is not involved at all other than you assume that the extra current must be flowing to ground somewhere. I assume that the test button works by connecting a resistor between hot after the GFCI circuit and nutral before the circuit. Finally, be aware that in houses where there is no ground run to the outlets (i.e. built before the National Electrical Code (or whatever the name actually is) reqired 3 prong outlets), the Code allows you to replace two prong outlets with GFCI three prong outlets with the ground lug unconnected! I originally read this fact in Popular Science magazine and it was confirmed by a code inspector for the city of San Jose. Because the GFCI will detect current flowing from the hot line to a ground (including through your body), this provides the same kind of protection as a conventional, properly wired 3 prong outlet. -- Ted Marshall ...!uunet!blia!ted ted@blia.bli.com ShareBase Corp., 14600 Winchester Blvd, Los Gatos, Ca 95030 (408)378-7000 The opinions expressed above are those of the poster and not his employer.