For mechanical security and continuity to ground, rigid conduit shall be provided with two (2) lock nuts, one inside and one outside the equipment to which it is attached. Metallic service equipment, rigid conduit, electrical metallic tubing, flexible conduit, metallic switch, outlet receptacle and junction boxes shall have a conductive coating or finish. Watertight couplings shall be employed for joining electrical metallic tubing. (1989 Code § 5-310)