CAT III vs CAT IV Multimeter: Which Rating You Need
Quick answer: CAT III covers the building installation: distribution panels, breakers, fixed wiring and permanently connected motors. CAT IV covers the source of that installation: the service entrance, the utility meter and the supply lines into the building, where a fault or a voltage spike carries far more energy. A CAT IV meter is built to survive a larger transient, so use one wherever you work upstream of the main overcurrent protection.
Most instruments in our multimeter range, our clamp meters and our non-contact voltage tester pens carry a marking such as "CAT III 600V". Check the marking on the specific model: basic tools such as neon screwdriver testers carry no CAT rating. This guide explains what that marking means, how CAT II, III and IV differ, and how to match the rating to the job. It also states plainly which of our instruments fit which category, and where they do not.
What a measurement category describes
IEC 61010-1 sorts mains circuits by where they sit in the low-voltage installation. The closer a circuit is to the supply source, the lower its source impedance. Low impedance means that if something goes wrong, the supply can push a large current into it, and a short inside a meter can turn into an arc flash.
The category is not about the steady voltage you read on the display. It is about the short spikes that ride on top of it: lightning on supply lines, utility switching, and large motors or capacitor banks switching on site. A meter has to absorb those transients without flashing over internally while your hands are on the probes.
Older editions of the standard also defined CAT I for protected electronic circuits not connected to mains. Current editions no longer use CAT I. A terminal that is not rated for mains measurement is marked as such, and it should never be connected to mains; if an input shows no CAT II, III or IV marking, treat it as not for mains.
CAT II vs CAT III vs CAT IV side by side
| CAT II | CAT III | CAT IV | |
|---|---|---|---|
| Part of the installation | Loads connected through a plug | The building installation | The source of the installation |
| Typical test points | Appliances, portable tools, outlets at a distance from the panel | Distribution panels, breakers, fixed wiring, bus bars, junction boxes, permanently connected motors, sockets close to the service | Service entrance, utility electricity meter, primary overcurrent protection, overhead and underground service lines |
| Energy available in a fault | Lowest of the three | Higher | Highest, greatest arc flash risk |
| Impulse withstand, 300V rating | 2500 V | 4000 V | 6000 V |
| Impulse withstand, 600V rating | 4000 V | 6000 V | 8000 V |
| Impulse withstand, 1000V rating | 6000 V | 8000 V | 12000 V |
The impulse figures are the values commonly used in IEC 61010 for each category and line-to-earth voltage. Note that a CAT IV 600V meter is designed for the same 8000 V transient as a CAT III 1000V meter.
That does not make them interchangeable. A CAT III 1000V meter is not automatically suitable for CAT IV work. The maker has to design and declare the instrument for that category, so trust the category on the marking, not arithmetic.
Why the category matters more than the voltage
Take a hypothetical pair: one meter marked CAT II 1000V and one marked CAT III 600V. The bigger number looks tougher. The table shows both are designed for a 6000 V impulse, but only the second is rated for a distribution panel, where the energy behind that impulse is higher. For panel work the CAT III 600V meter is the correct choice and the CAT II 1000V meter is not.
The voltage in a rating is the maximum working voltage to earth for that category. On a 230/400 V three-phase system with an earthed neutral, each phase sits at 230 V to earth. On systems without an earthed neutral, the voltage to earth can reach the full line-to-line value.
The voltage between the probes counts too. Measuring phase to phase on that panel puts 400 V across the meter, so it must stay within the meter's rated voltage as well. Use at least a CAT III 600V meter on 230/400 V three-phase panels.
Also keep the measuring range and the safety rating apart. The VC99 has a 1000V DC range, but its safety rating is CAT III 600V. The range tells you what the meter can display. The CAT marking tells you where it may be connected.
The meter is only as safe as its test leads
Probes and test leads are rated separately, under IEC 61010-031. The system takes the rating of its lowest-rated part. A CAT III 600V meter fitted with unmarked replacement leads is a meter with an unknown rating.
- Check that the leads carry a category and voltage at least equal to the job. Replacements are in our test lead range.
- For CAT III and CAT IV points, shrouded tips or probe caps are often required. They limit exposed metal and reduce the chance of bridging two conductors.
- Independent certification marks from a test lab show that a rating was verified. Look for them on the instrument and in its documentation; a printed CAT number alone is the maker's declaration.
Which category each job needs
- Electronics bench. Battery and protected low-voltage circuits need no mains category. If the same bench also handles mains-powered products, a CAT III meter covers both. The mains-powered VC8045 bench meter is rated CAT III 600V.
- Appliance and tool repair. Plug-connected loads are CAT II. A CAT III meter covers this work with margin.
- Panel, motor and building wiring work. CAT III, with a voltage to earth within the meter's rating. This is the core use of a CAT III 600V meter.
- EV workshop. An EV traction system is not part of the building installation, but it is still a high-energy circuit, so treat it with the same care as CAT III work. Check the vehicle's rated pack voltage in its service data before you start. Our CAT III 600V meters suit systems up to 600 V; 800 V class systems need a meter and leads rated CAT III 1000V, not our CAT III 600V models. Follow a proper high-voltage power-down procedure.
- Utility side. Service entrance, utility meter, overhead lines, underground service cables and outdoor feeders are CAT IV. Use a CAT IV rated meter here and nothing less.
Where our instruments fit, and where they do not
| Model | Type | Safety rating | Suitable for |
|---|---|---|---|
| VC86, VC99, VC890D | Multimeter | CAT III 600V | CAT III and CAT II, up to 600V to earth |
| VC835B, VC834 | Multimeter | CAT III 300V | CAT III and CAT II, up to 300V to earth |
| CM-2018, CM-2056 | AC/DC clamp meter | CAT III 600V | CAT III and CAT II, up to 600V to earth |
| VC1508PD, VC4060B+ | Insulation multimeter | CAT III 600V | CAT III and CAT II, up to 600V to earth |
| AC-3, AC-4 | Non-contact voltage tester pen | CAT III 1000V / CAT IV 600V | Live-wire screening, including CAT IV points up to 600V |
None of our multimeters, clamp meters or insulation multimeters is CAT IV rated. Do not use them at the service entrance, on the utility meter, on overhead lines or on outdoor feeders. For measurements there, buy a meter rated CAT IV for the voltage involved.
The AC-3 and AC-4 pens carry a CAT IV 600V rating, but they are non-contact detectors for 50Hz/60Hz AC, sensing 48V to 1000V by default or 12V to 1000V in high sensitivity. They warn you that a conductor is live; they do not measure its voltage. Treat a silent pen as a quick screen, not as proof that a circuit is dead.
The CAT III 300V models suit household and light commercial single-phase circuits. Use them only where neither the voltage to earth nor the voltage between the probes exceeds 300V, which rules out phase-to-phase work on 230/400 V panels.
Checks before you probe
- Read the rating on the meter and on both leads. The lower one is your rating.
- Inspect the leads for cracked insulation or exposed metal, and fit probe caps at CAT III and CAT IV points.
- Prove the meter on a known live source before and after the test, so a dead reading means a dead circuit and not a failed meter.
- Put the leads in the voltage jacks before measuring voltage. A lead left in the current jack shorts the source through the meter's fuse.
- Keep one hand clear where you can, stand on dry ground and wear the protective equipment your site rules require.
- Retire any meter with a cracked case or a burned input. Its rating no longer applies.
New to the instrument itself? Our beginner's multimeter guide covers jacks, ranges and common mistakes in detail.