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The bigger picture

Less guesswork.
More clarity.

Explore the connections behind the specs. A few clear labels, a little context, and the source for every fact.

A closer lookThe location changes the category.CAT II, III and IV describe different measurement environments. Follow the numbered locations from a plug-in load back toward the utility supply.

Tap a label to explore. You can also hover or use your keyboard.

CAT IIPlug-in appliances & tools

Receptacle-connected loads, such as household appliances and portable tools. The category describes the measurement environment; it does not give permission to work on live equipment.

Sources: 1: CAT II includes household appliances, portable tools and other receptacle-connected loads.
CAT IIIFixed wiring & distribution

The distribution part of the building installation, including distribution-panel devices and fixed-installation equipment. This is a different environment from a plug-in appliance.

Sources: 2: CAT III includes equipment in fixed installations and distribution-panel devices.
CAT IVUtility meter & service entry

The origin of the low-voltage installation, including electricity meters and the service entrance. Fluke also identifies the run between the meter and panel as CAT IV.

Sources: 3: CAT IV includes electricity meters, the service entrance and the run between meter and panel.

Illustrative locations, not a testing procedure. Match both the measurement category and voltage rating to the job. The lowest-rated meter, lead, probe or accessory limits the setup.

Source notes5 references

  1. CAT II includes household appliances, portable tools and other receptacle-connected loads.

    media.fluke.com — source for CAT II includes household appliances, portable tools and other receptacle-connected loads.
    Appliance, portable tools, and other household and similar

  2. CAT III includes equipment in fixed installations and distribution-panel devices.

    media.fluke.com — source for CAT III includes equipment in fixed installations and distribution-panel devices.
    distribution panel devices

  3. CAT IV includes electricity meters, the service entrance and the run between meter and panel.

    media.fluke.com — source for CAT IV includes electricity meters, the service entrance and the run between meter and panel.
    Electricity meters, primary overcurrent protection equipment

  4. Probes, test leads and adapters need the correct measurement category, voltage and amperage ratings.

    assets.fluke.com — source for Probes, test leads and adapters need the correct measurement category, voltage and amperage ratings.
    Use only correct measurement category (CAT), voltage, and amperage

  5. The lowest-rated component limits the measurement-category rating of the setup.

    assets.fluke.com — source for The lowest-rated component limits the measurement-category rating of the setup.
    Do not exceed the Measurement Category (CAT) rating of the lowest
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