If a metal water pipe is bonded to ground at one point, can I then use the other part of this pipe (e.g. on a different floor) as an extension of the ground wire to retrofit 2-prong outlets into 3-prong ones? This is of course to avoid having to run a long ground wire from the panel.
I think the NEC says you can't just tie the ground pin to any water pipe. But what about a water pipe that is known to be grounded?
According to peter :
Current NEC (and CEC) doesn't permit you to use water pipe as a grounding conductor[+]. Because now, or in the future, the conductivity of the pipe might be interrupted with plastic pipe, and now you have a ground that's highly dangerous - a hot-ground short in a device connected anywhere to that pipe will make EVERYTHING ELSE attached to that pipe (including the plumbing _itself_) live.
Could make a real bad day.
It's simpler, more cost effective, and safer to replace the 2 prong outlets with GFCIs. In fact, if you can figure out which outlet is "first" in every circuit, you can install one GFCI (for < $10), and substitute ordinary 3 prong outlets for all of the downstream
2 prong outlets. [Provided you use the little "protected by GFCI" stickers on all of the 3 prong outlets that don't have a real ground.] [+] "grounding conductor" means a conductor that connects a "to be grounded" device (say an outlet) to the grounding "electrode[s]" (the rod in the ground). The NEC/CEC _does_ require that metallic plumbing be grounded (so your plumbing doesn't go hot), and the NEC requires that underground metallic supply pipe is used as part of your grounding electrode system, but doesn't permit it to be used to supply grounding to circuits.
No. It's neither code, nor a good idea.
You *can* use GFCIs to replace two prong outlets. You must attach a label that says "No equipment ground". You will find these labels included in the GFCI package.
You can also use three prong outlets downstream of the GFCI. You must label these "GFCI protected", and "No equipment ground". You *cannot* connect a ground wire from the GFCI to the downstream outlets.
According to Seth Goodman :
More clearly: you MUST NOT connect _anything_ to the ground lug on the downstream outlets. In other words, you must not provide any ground pin continuity between the ungrounded outlets.
If you do, a hot-ground fault on one device in one outlet, will make all other grounded devices interconnected to that outlet (via the illicit grounds to other outlets) live.
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