About measurement categories (overvoltage categories)
To ensure safe operation of measurement products, IEC 61010 establishes safety standards for various electrical environments, categorized as CAT II to CAT IV *1, and called measurement categories. These are defined as follows.
- CAT II :
- Primary electrical circuits in equipment connected to an AC electrical outlet by a power cord (portable tools, household appliances, etc.)
- CAT III :
- Primary electrical circuits of heavy equipment (fixed installations) connected directly to the distribution panel, and feeders from the distribution panel to outlets.
- CAT IV :
- The circuit from the service drop to the service entrance, and to the power meter and primary overcurrent protection device (distribution panel).
Higher-numbered categories correspond to electrical environments with greater momentary energy, so a measurement product designed for CAT III environments can endure greater momentary energy than one designed for CAT II .
Using a measurement product in an environment designated with a higher-numbered category than that for which the product is rated could result in a severe accident, and must be carefully avoided. Never use a CAT I product in CAT II, III, IV environments. The measurement categories comply with the Overvoltage Categories of the IEC60664 Standards.
HIOKI products bearing the CE mark are designed in accordance with the requirements for the relevant measurement categories. To ensure safe use of measuring instruments, please use products displaying the appropriate CAT label for the intended location of use.
- In some cases, power lines may carry voltage spikes of several times the normal supply voltage. For reasons of safety, ordinary testers should not be used to measure power lines carrying more than 250V. When measuring such power lines, always use a tester with built-in overcurrent protection to guard against short circuits, such as Model 3008 and CAT III marked products.
Note : An industrial power line refers to a high-capacity supply circuit to equipment in factories or offices. A high-capacity supply circuit refers generally to a line carrying 20 A or more. This does not therefore include supply lines protected by overcurrent protection (fuses) or distribution breakers.
- To avoid short circuits and electric shock accidents when using a clamp-on sensor, use only with power lines carrying voltages within the rating limit of the sensor.
- To avoid short-circuits, bodily injury, and other hazards when opening the tips of the clamp core, avoid use with bare conductors.