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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.
128x128rja
elevick
2,636 posts
 
Using the BX shielding as your ground varies on building codes. The good thing is that if you have the shielding there and it's a home run to the box, you can ground it to the outlet on one end and the panel on the other. At a minimum consider using a GFI outlet in case this shield shorts somewhere...
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
jea48
4,425 posts
 
Back in 1961 steel boxes were used for rough-in boxes along with 2 wire Romex. In this case the metal box would not be grounded. A quick look inside would reveal a Romex clamp with a screw in the middle of the clamp holding down the Romex in place. You should also see the outer sheath of the Romex extending into the box beyond the Romex clamp.

Steel box with Romex clamp.
http://www.zoro.com/i/G0645337/?utm_source=google_shopping&utm_medium=cpc&utm_campaign=Google_Shopping_Feed&kpid=G0645337&gclid=CP-xkKyevcICFcGPMgodHVIADg
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