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No ground wire???

Recently moved to a house built in 1961. When replacing outlets found that there's no ground wire, two wires only. Boxes are steel and I think there's metal conduit in there. Is ground provided by the screws holding the outlet in the box? Effective? I would assume only if the conduit is grounded?

Have a newer box with circuit breakers and a lot of Romex coming out but not to my two audio outlets.

Any comments or opinions would be appreciated. Considering having an electrician run a new line for audio (which wouldn't hurt in any case). I would be more comfortable with a separate copper ground wire. All y audio stuff is three prong.
rja

Showing 1 response by gbart

gbart
290 posts
 
As said above, if the metal box is grounded via the armor of the bx cable, you only need to install a "self-grounded" outlet. It will work without requiring the grounding pigtail attached to the box. A self-grounding outlet is a three-prong type that has a brass tab at one mounting hole that grips the mounting screw to guarantee ground contact. Even if the screw works loose, the outlet will still always be grounded to the box. No GFI necessary.

Self grounding receptacle:
http://www.cesco.com/resources/078477/572667-ProductImageURL.jpg

Grounding via yoke to box contact:
http://i171.photobucket.com/albums/u292/stickboy1375/graphic.jpg
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