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Old 12-08-2011, 10:31 AM   #1
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Re: Installing Grounded Outlet in Metal Box


I recently posted a question about Installing a Grounded Outlet in a Metal Box to replace a Two Prong Polarized Outlet, the Box having a BX cable running to it from a metal Junction Box. I have come to the solution on my own I believe which is that because of the BX cable the Metal Box itself is Grounded and one can simply install the new Grounded Outlet without having to run a copper wire from the Box to the Green Screw because the metal plate of the outlet in contact with the Box is sufficient and this can be tested by simply using a common two prong tester one prong in the hot slot and the other in the second ground slot and if the 120 light comes on it's functioning. Correct??? If I'm wrong let me know.

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Old 12-08-2011, 11:18 AM   #2
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Re: Installing Grounded Outlet in Metal Box


Unless the receptacle is a self-grounding type (most aren't) then the ground wire from the receptacle to the box is still required.

I haven't seen your other thread, but the other thing to be aware of is that old armored cable (BX) is not approved as a grounding conductor. It needs to have a bonding strip, which is a small metal wire running inside the cable. Without the bonding strip, a test light may show that there is a ground, but it is not legal. Without the bonding strip, a ground fault ("short") could potentially just cause the cable's armor to heat up, instead of tripping a breaker.

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Old 12-08-2011, 11:30 AM   #3
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Re: Installing Grounded Outlet in Metal Box


Thanks for responding McSteve. As you'll appreciate I wanted to check this out before I plug my Computer in the new outlet.

1) How can I check to see if the Metal Strip is in the BX? Do I have to disconnect it to look inside?

2) Assuming the BX does have the metal strip, would you recommend me doing what I originally wanted to do which was to snip a piece of copper ground wire and attach it to the Box and the Green Screw on Receptacle?

3) Would I be better off pulling the BX and replacing with Romex, Copper ground to the Green Screw on receptacle?
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Old 12-08-2011, 11:59 AM   #4
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Re: Installing Grounded Outlet in Metal Box


1) It can be hard to tell if there is a bond strip; it is not required to be connected to anything, so it is usually either cut off flush at the end of the cable, or wrapped back along the sheath outside of the box. Either way can be hard to tell without seeing outside the box. But if you know the approximate age of the wiring, one of the professionals here can probably make a good guess.

2) If the BX does have a bonding strip, then your plan of connecting a piece of bare wire from the ground screw on the receptacle to a ground screw in the box is fine.

3) If the BX is older, without a bond strip, then running a new cable would be a good choice, if you're willing to open up the wall or whatever might be required to get the cable to the box. And assuming NM cable is allowed in your area.
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