Overvoltage category (OVC - Overvoltage category) IEC 60947-1. Annex H
Four overvoltage categories define the field of use for a device.
Cat. I. Devices supplied by a SELV isolating transformer or a battery.
Cat. II. Residential distribution, handheld or laboratory tools and devices connected to standardised 2P + earth electrical outlets (230 V).
Cat. III. Industrial distribution, fixed distribution circuits in buildings (main low voltage switchboards, rising mains, elevators, etc.).
Cat. IV. Utility substations, overhead lines, certain industrial equipment.