Two wire plus conduit ground

[michiganhotrod1]

Hi all;
I would like an opinion from the electrical experts here.
I have a 1930's commercial building in Detroit that is now my garage. It has a couple of 110 volt A/C circuits run with metal conduit, which are mostly buried in the floor concrete. The circuits are two wire, no ground wire, with two prong outlets.
My understanding of the code says that if I attach a ground wire via screw from the outlet to each outlet box, I can install three prong outlets and have safe, compliant, grounded circuits.
Am I correct in this understanding? There is about 2000 square feet in this portion of the building, so installing a separate green wire would be a lot of grief. Anything else I need to look out for?
Thanks for your help.
Mark

 

[frankush]

You'll be fine doing it that way. Don't forget the GFI protection. Seeing that it's been in the slab forever, you may want to check the continuity of the ground. Take a meter lead to the hot terminal of the existing receptacle and the other lead to ground. (Box or pipe) If you get 110V, the ground should be fine. Even if you don't have a ground, you can still install the GFI receptacle, but you'll have to label the outlet as not having a ground.

 

[theoldwizard1]

Don't forget the GFI protection.

I don't now about commercial applications, but residential garages require GFCI for all receptacles.

Even if you don't have a ground, you can still install the GFI receptacle, but you'll have to label the outlet as not having a ground.

Yep ! I installed a couple in my daughters house that has no ground wire (except were we have upgraded the wiring). About the only things that do not have a ground prong now a days are power tools !

BTW, the labels comes in the box with the GFCI receptacle.

 

[Charles (in GA)]

About the only things that do not have a ground prong now a days are power tools !

Except for lamps, and power supply bricks for cell phones, laptop computers, answering machines, and the like, toasters, and practically everything else in a house....... is two prong nowdays.

Charles