Measurement categories

IEC 61010 defines measurement categories to facilitate safe use of measuring instruments. Test and measurement circuits are classified into three categories according to the type of mains to which they are intended to be connected.

DANGER
Do not use a measuring instrument for measurements on mains that exceed the rated measurement category of that instrument. Do not use a measuring instrument without a designated measurement category rating for measurements on mains. Otherwise, the user will suffer from a serious bodily injury or the instrument and the mains installation will be damaged.

This instrument conforms to CAT III 300 V.

Measurement category II (CAT II)

Applicable to test and measuring circuits connected directly to utilization points (socket outlets and similar points) of the low-voltage mains installation.

EXAMPLE: Measurements on household appliances, portable tools, and similar equipment, and on the consumer side only of socket-outlets in the fixed equipment.

Measurement category III (CAT III)

Applicable to test and measuring circuits connected to the distribution part of the building’s low-voltage mains installation.

EXAMPLE: Measurements on distribution boards (including secondary meters), photovoltaic panels, circuit breakers, wiring, including cables, bus-bars, junction boxes, switches, socket-outlets in the fixed equipment, and equipment for industrial use and some other equipment such as stationary motors with permanent connection to the fixed equipment.

Measurement category IV (CAT IV)

Applicable to test and measuring circuits connected at the source of the building’s low-voltage mains installation.

EXAMPLE: Measurements on devices installed before the main fuse or circuit breaker in the building installation.