Safety Rating Category Guide

Safety Rating Categories

Category I

Electronic Equipment

• Protected electronic equipment
• Equipment connected to (source) circuits in which measures are taken to limit transient overvoltages to an appropriately low level
• Any high-voltage, low-energy source derived from a highwinding resistance transformer, such as the high-voltage section of a copier

Category II

Single-Phase Receptacle Connected Loads

• Outlet and long branch circuits
• Outlets at more than 10 meters (30 feet) from CAT III source
• Outlets at more that 20 meters (60 feet) from CAT IV source

Category III

Three-Phase Distribution, Including Single-Phase Commercial Lighting

• Equipment in fixed installations, such as switchgear and polyphase motors
• Bus and feeder in industrial plants
• Feeders and short branch circuits, distribution panel devices
• Lighting systems in larger buildings
• Appliance outlets with short connections to service entrance

Category IV

Three-Phase at Utility Connection, Any Outdoor Conductors

• Refers to the "origin of installation"; i.e., where low-voltage connection is made to utility power
• Electricity meters, primary overcurrent protection equipment
• Outside and service entrance, service drop from pole to building, run between meter and panel
• Overhead line to detached building, underground line to well pump