The exposed ends of cables where they enter fittings of any description, shall be protected and finished off so that moisture cannot enter the cable, or the insulating material, if of an oily or viscous nature, leak. Where unarmored cables or wires pass through metal frames, or into boxes or motor casings, the holes shall be substantially bushed with insulating bushings, and where necessary or required, with gas-tight bushings which cannot readily become displaced.