?
Tuesday, July 4, 2017
Question:
Re: CQD answer published Tuesday, June 27, 2017 -Grounding Electrodes
If the metal waterline is used as the primary grounding electrode and the supplemental is a rod type electrode then that supplemental rod type must be supplemented by one other (assuming the first is not 25 ohms or less) water pipe + rod + rod = adequate grounding. (assuming the first is not 25 ohms or less) but, a rod type electrode only, has to be supplemented by just one rod type electrode rod + rod = adequate grounding (assuming the first is not 25 ohms or less)
This to me, does not make much sense. I am sure that a water pipe 10 feet long has as much conductivity to ground as any rod type. I do not think this was the intent of the code. Can you give some reason that this was the intent? Thank you, Darren S. Benevento
A
Answer:
Hey Darren thanks for your follow up question. A metal underground water pipe has been accepted as a suitable grounding electrode for a long time. The reason for the supplemental electrode required by 250.53(D)(2), which can be a ground rod, is because if the metal water pipe is replaced it could be with a plastic pipe and the ground rod will then be the only electrode. So one ground rod that has a resistance of 25 ohms or less is acceptable as stated 250.53(A)(2)exception. If not a second rod or some other suitable electrode is necessary.