(5) Rod and Pipe Electrodes. Rod and pipe electrodes
shall not be less than 2.5 m (8 ft) in length and shall consist
of the following materials.
(a) Electrodes of pipe or conduit shall not be smaller
than metric designator 21 (trade size 3⁄4) and, where of iron
or steel, shall have the outer surface galvanized or otherwise
metal-coated for corrosion protection.
(b) Electrodes of rods of iron or steel shall be at least
15.87 mm (5⁄8 in.) in diameter. Stainless steel rods less than
16 mm (5⁄8 in.) in diameter, nonferrous rods, or their equivalent
shall be listed and shall not be less than 13 mm (1⁄2 in.) in
diameter.
nope........most of the time I use Galv.....