250.104 Bonding of Piping Systems and Exposed Structural
(C) Structural Metal.
Exposed structural metal that is interconnected
to form a metal building frame and is not
intentionally grounded or bonded and is likely to become
energized shall be bonded to the service equipment enclosure;
the grounded conductor at the service; the disconnecting
means for buildings or structures supplied by a feeder
or branch circuit; the grounding electrode conductor, if of
sufficient size; or to one or more grounding electrodes used.
The bonding jumper(s) shall be sized in accordance with
Table 250.66 and installed in accordance with 250.64(A),
(B), and (E). The points of attachment of the bonding jumper(
s) shall be accessible unless installed in compliance with
250.68(A), Exception No. 2.