Section 39.271. Grounding

(a) Unless otherwise provided by § 39.197(d) (relating to grounding), exposed noncurrent-carrying metal parts of lighting fixtures and other similar fixed electrical devices shall be permanently grounded when used under the following circumstances:

(1) When in locations where explosives, inflammable gas, or inflammable flyings normally exist in dangerous quantities.

(2) When within touching distance or about 8 feet from metal, concrete, or permanently damp floors or stairways, including fire escapes, galleries, or bridges, as in machine shops, stables, launderies, and the like.

(3) When readily accessible from the ground or floor and also within five feet of conducting surfaces, such as metal piping, metal radiators, stoves, furnaces, plumbing fixtures, damp walls or similar conducting surfaces, as in kitchens, machine shops, print shops, and the like.

(b) On grounded systems the center contacts of sockets and receptacles should be connected to the ungrounded side of the system, and the inner screw shell of the devices to the grounded side or neutral, in order to reduce the liability of breakdown of the dielectric between the inner screw shell and the grounded outer brass shell, and also reduce the liability of injury to persons in replacing lamps. This is especially important in wiring electric signs. In lieu of grounding the external metal parts of lamp sockets, if suitable means for grounding are not readily available, as sometimes is the case with knob and tube wiring not near plumbing fixtures, sockets and lamp guards or similar devices of suitable insulating material may be used, or the socket itself placed out of reach and arranged for its operation by a chain pull having adequate insulation in the chain.