To ensure an operators’ ability to use measuring instruments safely, IEC 61010 classifies the locations in which instruments are used into a series of safety-based measurement categories (ranging from CAT II to CAT IV). Using an instrument that does not satisfy the required safety level can lead to an electrical accident.

Ensuring Safe Operation of the Product

Measurement Category Under safety standards (EN61010 Series, JIS C 1010 Series), measurement is classified into Categories II to IV according to the measurement point's rated voltage to ground, current capacity (size of current that flows in a short-circuit fault), etc., and the transient overvoltage that occurs at the measurement point.

To help you use measuring instruments safely, the following information is provided in each product's Instruction Manual under "Specifications": • Rated voltage to ground: The measurement point's voltage level relative to ground, Measurement Category, Anticipated transient overvoltage, etc. • Location for use: Pollution Degree 2, indoor, altitude no more than 2000 m, etc.

  • Category II Measurement at a point from the power plug to the equipment's power circuits, where equipment is directly connected to an outlet.
  • Category III Measurement at a point on the power distribution cabling or power supply circuits, or at a point from the distribution panel to a distribution terminal behind an outlet, where equipment (for example a fixed installation) takes electricity directly from a distribution panel.
  • Category IV Measurement at a point on a service drop to a building, or on the line from the drop connection to the power meter or distribution panel.

The measurement instrument's Category is marked as "CAT II", CAT III" or "CAT IV" near the measurement terminals.

Never measure a measurement point with a higher category number than the category indicated on the measuring instrument. Doing so could lead to a serious accident such as electric shock.

You may want to read more about these specific Hioki products:

Hioki AC/DC Clamp Meter CM4372

Hioki Digital Multimeter DT4282