Vince O'Brien, Emeryville, CA
My daughter’s house was rewired in the 1950s. It has adequate wiring (#12 on the receptacles), but none of the circuits has a ground wire. Can I run a single ground to the receptacles, or do I need one for each circuit? Can I tie to cold-water pipes when they are available? (I’d make sure the pipes were grounded.)
Clifford A. Popejoy, a licensed electrical contractor in Sacramento, California, replies:
To answer your second question first, no, you can’t grab a ground from a cold-water pipe. Several years ago, this setup was allowed, but with the increased popularity of nonmetallic water pipe and fittings, there’s too much chance of an interruption in the metallic piping to allow its use for something as important as a grounding conductor. See 2002 National Electrical Code sections 250.130(C)(1) and 250.52(A)(1).
Even if the pipes are continuous when you install the ground wire, you can’t guarantee that the integrity of the ground would be continuous in the future, say, after a section of galvanized iron or copper pipe has been repaired with PVC. It’s not worth risking someone’s life.
Where do you attach the equipment-grounding conductor, then? Although the NEC allows a few other options [section 250.130(C)], the best place to connect a ground (when retrofitting) is on the ground bus of the panel where the circuit is connected to its breaker.
To answer your first question: In a retrofit situation where the ground is not part of the cable or in the same conduit, each circuit needs a separate grounding conductor. See NEC sections 250.122(A) and (C).
I’ve found that the appliances and tools typically used in many parts of the house don’t need a grounding outlet (i.e., one with an equipment ground). For receptacles where an equipment ground is needed for safety, like in the kitchen, outdoors, or in the garage, or for surge protection, I recommend running a new circuit. It usually isn’t much more work to run a new 14/2 or 12/2 nonmetallic cable than to run an insulated AWG 12 grounding conductor. Adding the new circuit also will provide more capacity and a better equipment ground.