CAT Ratings Explained

Understanding CAT Safety Ratings for Multimeters and other Test Instruments

National Fire Protection Association has addressed electrical safety issues in the NFPA 70E standard that has been adopted throughout the United States and copied intenationally. Test instruments, such as multimeters, from reputable manufacturers are designed to comply with NFPA 70E category requirements (CAT Ratings). CAT Ratings are based on the location where test instruments will be used.

The other part of the equation is properly selecting and then using the equipment. The following illustration and table of CAT Ratings I-IV summarizes the locations.

Photo from Fluke's "ABCs of Multimeter Safety" showing locations where CAT ratings I - IV apply Click photo to download the Application Note and learn more

Overvoltage Category	In Brief	Examples
CAT 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
CAT 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
CAT II	Single-phase receptacle connected loads	Appliance, portable tools, and other similar household loads Outlet and long branch circuits Outlets at more than 10 meters (30 feet) from CAT III source Outlets at more than 20 meters (60 feet) from CAT IV source
CAT I	Electronic	Protected electronic equipment Equipment connected to (source) circuits in which measures are taken to limit transient overvoltages to an approximately low level Any high-voltage, low-energy source derived from a high-winding resistance transformer, such as the high-voltage section of a copier

When choosing a multimeter, first determine CAT levels you will be operating. Then choose a meter with a voltage rating higher than the maximum voltage you will be testing at each CAT level. For example, an electrician working in CAT III and CAT IV areas can choose a meter rated CAT III 1000 V / CAT IV 600 V. Within a category, a higher voltage rating denotes a higher transient withstand rating, e.g., a CAT III-1000 V meter has superior protection compared to a CAT III-600 V rated meter. The real misunderstanding occurs if someone selects a CAT II-1000 V rated meter thinking that it is superior to a CAT III-600 V meter. Select a meter with the voltage rating suitable for the location (i.e. CAT I, II, III, IV) where you will be operating.