(a) Each transmission line shall be installed with at least 12 inches (305 millimeters) of clearance from any other underground structure not associated with the transmission line. If this clearance cannot be attained, a minimum clearance of two inches (51 millimeters) must be attained provided the transmission line is protected from damage that might result from the proximity of the other structure.
(b) Each distribution main shall be installed with at least six inches (152 millimeters) of clearance from any other underground structure to allow proper maintenance and to protect against damage that might result from proximity to other structures. If this clearance cannot be attained, the main may be installed with a minimum clearance of two inches (51 millimeters), provided the main is suitably protected from damage that might result from the proximity of the other structure.
(c) In addition to meeting the requirements of subdivisions (a) and (b) of this section, each plastic pipeline must be installed with sufficient clearance, or must be insulated, from any source of heat so as to prevent the heat from impairing the serviceability of the pipe.