Covers optical isolators, also called optical couplers or photo-couplers, intended (1) to provide signal transfer between dielectrically isolated circuts, (2) for use in equipment with a supply voltage not exceeding 600 volts ac rms or dc, and (3) for use as components in devices and appliances. The standard also covers the electrical insulation properties of the insulation properties of the insulation between the isolated circuits of the optical isolator.