250.52 Grounding Electrodes.
(A) Electrodes Permitted for Grounding.
(1) Metal Underground Water Pipe. A metal underground
water pipe in direct contact with the earth for 3.0 m (10 ft) or
more (including any metal well casing bonded to the pipe) and
electrically continuous (or made electrically continuous by
bonding around insulating joints or insulating pipe) to the
points of connection of the grounding electrode conductor and
the bonding conductor(s) or jumper(s), if installed.
(2) Metal Frame of the Building or Structure. The metal
frame of the building or structure that is connected to the
earth by one or more of the following methods:
(1) At least one structural metal member that is in direct
contact with the earth for 3.0 m (10 ft) or more, with or
without concrete encasement.
(2) Hold-down bolts securing the structural steel column
that are connected to a concrete-encased electrode that
complies with 250.52(A)(3) and is located in the sup-
port footing or foundation. The hold-down bolts shall
be connected to the concrete-encased electrode by
welding, exothermic welding, the usual steel tie wires,
or other approved means.
(3) Concrete-Encased Electrode. A concrete-encased elec-
trode shall consist of at least 6.0 m (20 ft) of either (1) or (2):
(1) One or more bare or zinc galvanized or other electri-
cally conductive coated steel reinforcing bars or rods of
not less than 13 mm ( 1 ⁄ 2 in.) in diameter, installed in
one continuous 6.0 m (20 ft) length, or if in multiple
pieces connected together by the usual steel tie wires,
exothermic welding, welding, or other effective means
to create a 6.0 m (20 ft) or greater length; or
