The rated voltage of the apparatus — the maximum voltage at which it is designed to operate — determines classification. Equipment rated for voltages exceeding 1,000 V classifies here under 8535, while apparatus rated at 1,000 V or below falls under 8536. The rated voltage appears on the nameplate and in the manufacturer's technical specification; the actual operating voltage in a given installation is not the determining factor.

Lightning arresters, voltage limiters, and surge suppressors designed for circuits exceeding 1,000 V classify under 853540. Devices intended for low-voltage circuits (not exceeding 1,000 V) belong in the parallel heading for low-voltage apparatus. For combination devices that protect across a wide voltage range, the rated maximum voltage and the primary application environment guide classification.