A: The CAT III & IV ratings defines the overvoltage installation categories that applies to low voltage systems of <1000 Volts test equipment as defined in IEC 1010 and UL61010-1 standards. This describes an electrical components ability to withstand impulse/transient voltage. The rating of our voltage indicators allows their use as permanently mounted test equipment used in fixed installations such as switchgear, MCCs, bus and feeder in industrial plants and low voltage connections made to utility power.
The lower the number, the less impulse the item can withstand and also the further downstream from the voltage source the component can be installed or used. CAT III is for distribution wiring, including main busses, feeders, and branch circuits with permanently installed loads. The highest is CAT IV, which is installation at the origin or at the utility level. Our devices are rated for 600V at CAT IV, for applications between 600 and 750V, they are CAT III rated.