This will be handled by an electrician, but I wanted to get info on what's permissible as my first stab at talking to an electrician led to a conclusion that seems disallowed and unsafe (entirely isolated ground system for an antenna).
We have a 1950's house with the service entrance at a back corner and the water main entrance near the center of the front of the house. It looks like the primary grounding for this house is a 4 gauge conductor from the panel through conduit buried in the slab and bonded to the water main a foot or so after it enters the house.
A new antenna connection penetrates the house near the water main and has a lightning arrester in-line, currently connected to nothing.
Questions:
- Does it make sense that that water main (about 50-80 feet away from the main panel) is the primary GEC for the house?
How to bond the lightning arrester bus bar:
-
New ground rod outside, > 16 feet from water main, bonded via approved clamp to water main outside
-
New ground rod outside, > 16 feet from water main, with 4 ga conductor running inside and then about 10 feet and also clamped separately to water main near entrance.
or #2/#3 without the new ground rod.
The first electrician who I talked to said "just drive a ground rod, at least 8 feet, and call it a day," but didn't have anything to say about tying it to the house electrical grounding system.
Best Answer
The water main is a grounding electrode, but not a grounding electrode conductor
You are correct that a metal water service line is considered a primary grounding electrode when present; however, not the least due to the potential for the utility to replace said metal water service line with a nonconductive, non-grounding plastic water service line, the NEC requires a supplemental "made electrode", usually a pair of ground rods 8' long and 6-8' minimum apart, when the primary electrode is a water service line. For these rods, NEC 250.66(A) lets you use 6AWG copper to tie them back to the main grounding electrode conductor.
However, you must tie those rods back to the grounding electrode conductor in addition to tying the lightning arrestor grounding wire to said ground rods. (This is required by NEC 250.50 and 800.100(B)(2) or 800.100(D).) Furthermore, the reason you see the Grounding Electrode Conductor tied to the grounding electrode at the service entrance point is because NEC 250.68(C)(1) requires that connection to be made within 5' of where the water service enters the house. (This requirement exists so that a plumber doesn't accidentally leave your house afloat in the electrical sense of the term.)
So, I would use plan #3, but modified with the addition of a second rod, and more importantly modified to use either a split-bolt or a T-tap connector (Ilsco GTT-2-2 or equivalent) to connect the bonding jumper to the GEC directly without having to sever the latter. You can connect the lightning arrester's bonding wire the same way for now; generally speaking, though, you'll want to put in an Intersystem Bonding Termination device at the main panel if at all possible, as that provides a central place for future communications grounding wires to land.