CAT ratings explained: which meter is safe for the job

Every multimeter and clamp meter carries a measurement category and a voltage, such as CAT III 600 V. The category says where in the electrical system the meter is built to survive a transient (a spike from a switching event or a lightning strike nearby); the voltage is the working voltage it is rated for at that category. The rating is set by the IEC 61010 safety standard, which the makers test against and publish. Here is how to read it, with the figures each maker publishes for the meters on this site.

The four categories

Each step up expects a bigger transient at the same working voltage, so a CAT IV 600 V meter is built for a harsher environment than a CAT III 600 V one, and a CAT III 1000 V meter for a higher working voltage than a CAT III 600 V one. Pick the meter by the highest category and voltage you will work in, not the lowest.

The voltage number is not interchangeable with the category

CAT III 1000 V and CAT IV 600 V are both common on electricians' meters, and they are not the same thing. The first is rated for a 1000 V working voltage at distribution level; the second for 600 V at the service entrance. A meter can carry both marks (many of the ones below do), and then each applies in its own location. In a US residential or light commercial job the working voltage is 120/240 V or 277/480 V; the category is what changes between the panel and the meter base.

The leads count as much as the meter

The rating that applies is the lowest of the meter, the test leads and any probe or clamp attached. Leads are marked separately (Fluke's TL75 leads and Klein's leads with CAT III/CAT IV safety caps are examples), so a CAT IV 600 V meter used with CAT II leads is a CAT II measurement. Check the leads in the box on each meter's page before relying on the meter's own mark.

Rated CAT IV 600 V (service entrance) on the maker's page

These meters publish a CAT IV 600 V rating, most alongside CAT III 1000 V.

Rated CAT III 600 V, with CAT IV 300 V where stated

These publish CAT III 600 V. The Fluke 320-series clamps add CAT IV 300 V; the Fluke 110-series multimeters and the Milwaukee meters publish CAT III 600 V only.

Before you buy

Researched by Rob, licensed electrician (Australia). Deal mechanics described here are the makers' usual promotion types; check the exact terms on the retailer's offer. Found an error? Tell us.

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