I was just reading the bible (code book of course), and now I am confused. I have always used the meathods in 250.30 for hooking up the grounding electrode to the derived neutral. 250.30(a)(3) states "the grounding electrode shall be the nearest one of the following, grounded metal structure, grounded metal water pipe within 5' of entrance, or other electrodes. I have always used the grounded metal structure as it has always for me been the closest. So I have never gone to the water pipe. Now I read 250.104(a)(4), it states that the grounded conductor of the seperatly derived system shall be bonded to the nearest available point of the interior metal water piping system. I have never seen anyone else do this either? Have I and all the installations I have seen been missing this? Thanks............Brian
Most service neutrals are bonded to the water line as well as the building steel,so technically your neutral is bonded to the water line,because the water line is bonded to the steel at the main service.
The reason for bonding the local water pipe to the SDS is to make sure that the local metal piping could not become energized by a ground fault. There is the possibility that the local water piping is isolated from the main service bonding jumper by some type of nonmetallic pipe or fitting. The code requires the local bond at the SDS and does not permit you to rely on the main bonding at the building service. Don
Exception: A separate water piping bonding jumper shall not be required where the effectively grounded metal frame of a building or structure is used as the grounding electrode for a separately derived system and is bonded to the metallic water piping in the area served by the separately derived system.
That is in the 2002 code book. If you use the "." in place of the "-" to separate the article number form the section number most here will assume that you are using the 2002 code. The "-" was used in all of the codes prior to 2002.