Plumbing used as equipment ground?

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Old 09-24-02, 06:50 AM
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Plumbing used as equipment ground?

My 36-year-old home has knob and tube wiring, but also is grounded (you can see the green ground wire in the knob and tube fixtures in the attic). A tester shows that all outlets are "correct" (i.e., no open ground). A piece of heavy aluminum wire (prob. 4 ga.) runs from the neutral/grounding bus of the main panel to the main cold water pipe. Here's the potential problem: nearby, on the same pipe, is another clamp to which is attached a single piece of solid 12 or 14 ga. wire, which goes into loom and then disappears into the wall. My guess is that someone ran this to provide an equipment ground in an area where for some reason the original grounding didn't go. Is this a problem?
 
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Old 09-24-02, 08:00 AM
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This is probably okay. Although connecting an equipment ground to the plumbing is normally disallowed and a very bad idea, when the panel ground and the equipment ground are both connected to the plumbing within five feet of where it enters your house, this is allowed. Because the equipment ground and the panel ground are near each other, only a short section of the plumbing is used as a grounding conductor.
 
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Old 09-24-02, 08:58 AM
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Thanks for the quick reply. Should I 1) connect them to the same clamp; 2) move them closer together; or 3) leave it alone?
 
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Old 09-24-02, 09:35 AM
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If they are both within 5 feet of where the plumbing enters your house, leave it alone.
 
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