There may be requirements other than the NEC where you are working.
The NEC requirements are:
- Power earthing may have one or many electrodes that are connected
together as an earthing system (250.50).
- A metal water service pipe MUST be used as one of the earthing
electrodes. It has been so since time began. Exact requirements have
changed over time as more water services use plastic pipe. The
requirement for many years is that a metal water service pipe in contact
with the earth for 10 ft MUST be used as an earthing electrode. (250.50,
250.52)
- If the water service pipe is NOT metal-10ft, then the interior metal
water pipe must be "bonded" to the power ground system (250.104-A). The
connection as an earthing electrode (above) is more stringent than
"bonding".
- Since a metal water service may be replaced by plastic, a
"supplemental" electrode has been required for many years. Many kinds of
electrode can be used (250.53-D). Often it has been a ground rod because
they are easy to install.
- Gas piping must be "bonded" to the building ground system. The size of
the bonding wire is determined by the current rating of the circuit that
is likely to energize the pipe. In a house this is likely the feed
circuit for a furnace, or similar device. "The equipment grounding
conductor for the circuit that is likely to energize the piping shall be
permitted to serve as the bonding means." (250.104-B)
- Gas service pipe may not be used as an earthing electrode.
- Structural steel may be required to be used as an earthing electrode
(250.50, 250.52). Else it is required to be "bonded" (250.104-C).
Connection as an earthing electrode is more stringent than "bonding".
- For new construction, if there is a concrete foundation or footing, a
"concrete encased electrode" is required (250.50, 250.52) These are
commonly called a "Ufer" ground. They are a good electrode (far better
than a ground rod) and are used as the "supplementary" electrode for a
water service pipe where both are present.
- Ground rods are required to be used as an earthing electrode "where
present". They won't be present unless someone installs one. Installing
one is not required. (250.50)
Rods are 8 ft min, and the types used are 5/8" diameter. They must have
a resistance to earth of 25 ohms or less, or else 2 can be used and
there is no requirement (250.53-A-2).
Ground rods are among the worst earthing electrodes. If you connect a
120V circuit to a code compliant 25 ohm rod will it blow a 15A fuse?
If the only earthing electrode is a ground rod (which is compliant is
some places), and the rod has a near miraculous resistance to earth of
10 ohms, and there is a surge to earth of 3,000A, the potential of the
building "ground" is 30,000V above 'absolute' earth potential. In
general, 70% of the voltage drop away from the rod is in the first 3 ft.
Over 3 ft from the rod is at least 21,000V from the building "ground"
system. If you have a rooftop TV antenna that is earthed only to a
separate rod the coax will be over 21,000V from the power "ground". You
may also get that on a metal gas service pipe, which is why very
thin-walled CSST can be a problem.
What I wrote is consistent with NEC requirements.
Installing earthing systems has been part of my job for the past
...um... lots of years.