wjm@lcuxc.UUCP (B. Mitchell) (02/04/85)
<gulp> In most cases, the metal ears on a grounded receptacle (wall outlet) are NOT adequate to provide an equipment grounding conductor between the receptacle and the box. The National Electrical Code (and most local codes) specifically forbids using the screws that hold a receptacle to the box for grounding purposes, unless UL (or other recognized testing laboratory) has specifically listed (approved) the receptacle for this purpose. Approved receptacles will have the letters 'FS' stamped on them, next to the UL logo, and they have a metallic springlike strip that "bites into" the threads on the screw, insuring a good electrical connection. Otherwise, it is likely that the support screws may provide a good support but a poor electrical contact for the grounding conductor. If the receptacle is not of the 'FS' type, the Code requires a bonding jumper (a short piece of bare or green insulated wire - at least #14 for most residential general purpose 15 or 20 amp circuits) to bond the receptacle to a metallic box. The Code requires that metallic boxes be grounded. This is accomplished by connecting them to the conduit (if conduit is used for wiring), the armor of armored (BX) cable, or to the ground wire of non-metallic cable (including type UF). Non-metallic boxes (which can only be used with non-metallic cable) (and are not permitted by some local codes) need not be grounded, so you connect the ground terminal of the receptacle to the ground wire of the non-metallic cable. The Code also requires that metal cover plates be grounded, and this is accomplished by the screw that connects the plate to the receptacle. The reason receptacles are furnished with plaster ears is that in some places, the box is set back from the wall surface (which I regard as bad practice and would raise %^*%^ with any electrician who worked for me that I caught doing it) and the ears allow the receptacle to be set flush with the wall. They are detachable, and often have to be detached (you break them off with a pair of pliers) to fit in some places, including some surface-mount cover plates. By the way, the same grounding rules apply to surface mount boxes as well as the flush ones we've been talking about. The cover can only be used to ground the receptacle to the box IF it is specifically approved for the purpose (this is a new provision in the 1984 version of the National Electrical Code). Otherwise, a bonding jumper must be used. 73's Bill Mitchell, WB2IAU, PE (ihnp4!lcuxc!wjm)