Metal cable trays, metal raceways, and metal enclosures for conductors shall be grounded, except that:
Metal enclosures such as sleeves that are used to protect cable assemblies from physical damage need not be grounded; and
Metal enclosures for conductors added to existing installations of open wire, knob-and-tube wiring, and nonmetallic-sheathed cable need not be grounded if all of the following conditions are met:
Enclosures are free from probable contact with ground, grounded metal, metal laths, or other conductive materials; and
Frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and metal outlet or junction boxes that are part of the circuit for these appliances shall be grounded.
Exposed noncurrent-carrying metal parts of fixed equipment that may become energized shall be grounded under any of the following conditions:
If within 2.44 m (8 ft) vertically or 1.52 m (5 ft) horizontally of ground or grounded metal objects and subject to employee contact;
If located in a wet or damp location and not isolated;
If supplied by a metal-clad, metal-sheathed, or grounded metal raceway wiring method; or
If equipment operates with any terminal at over 150 volts to ground.
Notwithstanding the provisions of paragraph (g)(6)(iv) of this section, exposed noncurrent-carrying metal parts of the following types of fixed equipment need not be grounded:
Enclosures for switches or circuit breakers used for other than service equipment and accessible to qualified persons only;
Electrically heated appliances that are permanently and effectively insulated from ground;
Distribution apparatus, such as transformer and capacitor cases, mounted on wooden poles, at a height exceeding 2.44 m (8.0 ft) above ground or grade level; and
Listed equipment protected by a system of double insulation, or its equivalent, and distinctively marked as such.
Exposed noncurrent-carrying metal parts of cord- and plug-connected equipment that may become energized shall be grounded under any of the following conditions:
If operated at over 150 volts to ground, except for guarded motors and metal frames of electrically heated appliances if the appliance frames are permanently and effectively insulated from ground;
Refrigerators, freezers, and air conditioners;
Clothes-washing, clothes-drying, and dishwashing machines, sump pumps, and electric aquarium equipment;
Hand-held motor-operated tools, stationary and fixed motor-operated tools, and light industrial motor-operated tools;
Motor-operated appliances of the following types: hedge clippers, lawn mowers, snow blowers, and wet scrubbers;
Cord- and plug-connected appliances used in damp or wet locations, or by employees standing on the ground or on metal floors or working inside of metal tanks or boilers;
Portable and mobile X-ray and associated equipment;
Tools likely to be used in wet and conductive locations; and
Notwithstanding the provisions of paragraph (g)(6)(vi) of this section, the following equipment need not be grounded:
Tools likely to be used in wet and conductive locations if supplied through an isolating transformer with an ungrounded secondary of not over 50 volts; and
Listed or labeled portable tools and appliances if protected by an approved system of double insulation, or its equivalent, and distinctively marked.
Metal enclosures for service equipment shall be grounded.