Tools & Safety

Meter CAT Ratings: Choosing a Tester That Won’t Fail You

CAT II, CAT III, CAT IV: what the measurement categories on a multimeter mean, and why voltage alone doesn’t tell you if a meter is safe for the job.

By IES team, Innovative Electrical Services (IES), Auburn, CA · Reviewed November 2026 · 2 min read

Key takeaways
  • Measurement categories describe how much surge energy a meter may face, based on where it is used.
  • CAT II: plug-in loads. CAT III: panels and building wiring. CAT IV: the service and utility side.
  • Choose a meter rated for both the category and voltage you’ll touch.
  • Test your tester on a known live source before and after (live-dead-live).

A multimeter looks like a simple tool, but it is the one thing standing between an electrician’s hands and the circuit while testing. Meters are rated under the IEC 61010 safety standard by measurement category (CAT) and voltage, and those markings matter more than most people realize.

Why categories exist

The danger isn’t just the steady voltage. Short transient spikes, from lightning, switching or motors, travel on the wiring, and they are biggest closer to the utility because there is less impedance to soak them up. A meter that can’t withstand a spike can fail internally and start an arc in the user’s hands.

CAT IVservice drop, meter,service entranceCAT IIIpanels, feeders,hard-wired equipmentCAT IIreceptacles andplug-in appliancesmore surge energyless surge energyUse a meter rated for the highest category and voltage you will touch.
Measurement categories (from the IEC 61010 safety standard) describe how much surge energy a meter may meet. The closer to the utility, the higher the category you need.

The categories

  • CAT II: single-phase receptacle-connected loads, such as appliances and portable tools, at a distance from the panel.
  • CAT III: the building’s distribution, including panels, feeders, short branch circuits and hard-wired equipment.
  • CAT IV: the origin of the installation: the service drop, meter, service entrance and outdoor conductors.

(CAT I, for protected electronic circuits, was dropped in recent editions of the standard. You may still see it on older meters.)

Category beats voltage

Higher category means more transient protection at the same voltage. A CAT III 600 V meter is built to survive a bigger transient than a CAT II 1000 V meter, even though its voltage number is lower. For residential and light commercial work, a meter rated at least CAT III 600 V, and ideally CAT IV for service work, is the sensible baseline. Test leads and probes have ratings too, and the lowest-rated part sets the rating of the whole setup.

Habits that keep people safe

  • Use the live-dead-live test: check the meter on a known live source, test the circuit, then check the meter again.
  • Look for an independent testing lab mark on the meter, not just the maker’s claim.
  • Inspect leads for cracked insulation and replace damaged ones.
  • Use probe tip guards where possible to reduce the risk of slipping and shorting.
  • Non-contact voltage testers are handy for a quick check but aren’t a substitute for a contact test before work.

Sources and further reading

  1. Fluke, Multimeter safety and measurement categories guide
  2. NFPA free access to codes and standards (read the NEC online)

Local rules decide. These articles explain general ideas and point to the code sections we use. They are not legal or engineering advice and don’t replace the code itself. California adopts the NEC with its own amendments, cities and counties can add more, and the local inspector (the AHJ, or authority having jurisdiction) has the final say on any job. Read the code free at NFPA’s free access page.