Xref: utzoo misc.consumers:4905 misc.consumers.house:2228 sci.electronics:2950 Path: utzoo!attcan!uunet!husc6!cmcl2!rutgers!mtunx!whuts!homxb!hou2d!hz1 From: hz1@hou2d.UUCP (H.ZARETSKY) Newsgroups: misc.consumers,misc.consumers.house,sci.electronics Subject: the truth about GFCI's Keywords: GFCI outlets on two wire circuits Message-ID: <2005@hou2d.UUCP> Date: 11 May 88 14:14:23 GMT Distribution: na Organization: AT&T Bell Laboratories, Holmdel Lines: 56 here is the untold truth about gfci's for all those who want to know. the following is from a top engineer at Leviton Manufacturing. i happen to have worked there for a year and i am still friendly with the engineers there. for those who never heard of Leviton, they are one of the biggest manufactures of electrical supplies (outlets, switches, gfi's, home control systems, etc.) and anybody who has done any electrical work is familiar with them. there has been some articles on the network about gfci's and i want to clarify the use and operation of gfci's to all that don't know or are unsure. so here it is straight from the horse's mouth uncensored. ============================================================================== The GFCI compares current in the phase (hot) wire to the current in the neutral (return) wire. As long as the two currents are equal, the assumption is that there is no ground fault. A key requirement (and that is met for all utility supplied electrical systems) is that the neutral be grounded at the service entrance. If there should be a ground fault (current from the hot wire through the victim to ground) the GFCI detects an imbalance in current. If of sufficient magnitude , (5 ma) the GFCI will trip (the time spec is 25 ms to open the circuit) Note that a ground wire is NOT required for GFCI operation. This is one of the original purposes of GFCI's. Thus, the GFCI WILL protect two wire receptacles down stream. There are two additional points to be made. 1. The receptacle GFCI does have a ground hole for the round pin in a plug to access. This is put there for additional safety, belt and suspenders. 2. If a GFCI is used with two wire receptacles, only two wire recptacles can be used in the other branch circuit locations. The reason is so that the user won't think the additional protection is available when it isn't. The exception to the above is naturally if there indeed is a ground connection available in the boxes, but two wire receptacles were originally installed because of economic or other considerations. A very good explanation of application aspects of the GFCI is in a publication from NEMA, and can be purchased from them. NEMA (National Electrical Manufacturers Assoc.) 2101 L Street NW Washington DC 20057 202-457-8400 ask for: "Application Guide for Ground Fault Circuit Interrupters" Standards Publication No. 280-1984 ============================================================================= well folks there it is. i hope it helps. howie z.