Guide · Meters, supplies and scopes
Multimeter CAT ratings explained
What CAT I to CAT IV mean on a multimeter, which category a repair bench needs, and why an independent certification mark matters more than a printed label.
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Picks that fit
- Fluke 17B+ digital multimeter (600 V CAT III)Check price on Amazon
- UNI-T UT61E+ true-RMS digital multimeterCheck price on Amazon
Short answer
A CAT (measurement category) rating tells you which part of an electrical system a meter is designed to measure in. CAT II covers equipment plugged into outlets, CAT III covers distribution wiring and fixed installations, and CAT IV covers the utility connection.[1] Higher categories mean higher-energy transients, so choose a meter rated for the highest category you will measure in, and look for an independent certification mark rather than trusting a printed label.[2]
Picks that fitAll picks and how to choose
- Fluke 17B+ digital multimeter (600 V CAT III)Check price on Amazon
- UNI-T UT61E+ true-RMS digital multimeterCheck price on Amazon
The four categories
Fluke, summarizing the IEC 61010-1 categories, describes them like this:[1]
| Category | Fluke's description | What it means at a repair bench |
|---|---|---|
| CAT I | Protected electronic equipment | Circuits already protected from mains transients |
| CAT II | Single-phase receptacle-connected loads, such as appliances and portable tools | Measuring on equipment that plugs into a wall outlet |
| CAT III | 3-phase distribution, including single-phase commercial lighting, and equipment in fixed locations such as switchgear and polyphase motors | Fixed building wiring and distribution equipment: electrician territory for most readers |
| CAT IV | 3-phase at the utility connection, outdoor conductors, electricity meters and service entrances | The utility side; not a repair-bench job |
Fluke explains that a higher CAT number means an electrical environment with more power available and higher-energy transients.[2] A transient is a brief voltage spike on the supply. A meter built for a higher category is designed to withstand bigger ones, which is why the category matters more than the display or the feature list when mains is involved.
Category and voltage go together
A rating is printed as a category plus a voltage, such as "CAT III 600 V". Read both parts. The category says which environment the meter is built for; the voltage is the highest working voltage it is rated for in that category. A rating with no voltage, or a voltage with no category, tells you little.
Which category does a repair bench need?
- Battery- and USB-powered boards. These circuits are not connected to mains, so the CAT rating is not what limits you. It starts to matter the day the same meter touches anything plugged into an outlet.
- Equipment that plugs into an outlet. Soldering stations, power supplies and appliances are receptacle-connected loads, which Fluke places in CAT II.[1] US outlets supply 110-120 V,[3] so the meter's CAT II voltage must cover that with margin.
- Building wiring and panels. Distribution and fixed installations are CAT III.[1] For most readers, this is a job for a licensed electrician, not a bench meter.
A printed label is not proof
Anyone can print "CAT III" on a plastic case. Fluke's advice is that test tools should be independently evaluated to show they survive voltage transients, and certified by a recognized lab; it names CSA, UL, TÜV and Intertek (ETL).[2] CSA Group, UL, Intertek and two TÜV companies appear on OSHA's list of Nationally Recognized Testing Laboratories.[4]
The safety standard behind meter ratings is IEC 61010-2-033. Its third edition, published in 2023, covers hand-held multimeters for domestic and professional use that can measure mains voltage.[5]
How to check a meter:
- Find the rating on the meter itself, not just in the listing text.
- Find an independent certification mark on the meter or in its manual, such as UL, ETL, CSA or TÜV.
- Look the model up with the certifier. Intertek, for example, lets you check ETL listings in its Directory of Listed Products.[6]
- Check the test leads. Use leads marked for at least the same category and voltage, and replace any with cracked or nicked insulation.
- No marking, no mains. If you cannot find a rating, use the meter only on low-voltage circuits.
For what the marks themselves mean, see UL, ETL, CE and FCC marks explained.
A meter with a maker-stated CAT III rating
If your meter will touch anything plugged into an outlet, start from a maker's rating rather than a listing's. Fluke rates its 17B+ at CAT III 600 V under IEC 61010-1, with ranges up to 1000 V AC/DC and 10 A.[7] CAT III is a higher category than CAT II, the one Fluke assigns to equipment plugged into outlets.[1] A maker's rating is still not an independent certification, so step 2 above still applies: look for an independent mark on the meter itself.
Picks that fit1 product
Choose the Fluke 17B+ (CAT III 600 V, 2 AA batteries). On Amazon, buy only when 'Ships from / Sold by' shows Amazon.com or Fluke; other sellers may not be authorized Fluke channels.
More on choosing
Read the rating and any lab mark on the meter when it arrives.
Fluke 17B+ digital multimeter (600 V CAT III)
A bench meter for low-voltage work
If your work stays on battery- and USB-powered boards, you can choose a meter for its bench features, such as true RMS AC readings, but read its rating before it goes near an outlet. The UNI-T UT61E+ listing, from a store named UNI-T Direct Store, does not show a CAT rating, so the marking on the meter is the only place to confirm it. That is the difference from the Fluke 17B+, whose rating Fluke publishes.
Picks that fit1 product
Choose the UT61E+. The AliExpress listing does not show a CAT rating, so read the rating printed on the meter itself before you measure anything plugged into an outlet.
More on choosing
On Amazon, check that 'Ships from / Sold by' shows Amazon.com or UNI-T Direct before you buy.
UNI-T UT61E+ true-RMS digital multimeter
Next
Questions
Do I need CAT II or CAT III for electronics repair?
For equipment that plugs into an outlet, CAT II is the matching category; Fluke places distribution wiring and fixed installations in CAT III. If the same meter might ever be used on building wiring, choose the higher category.[1]
Does a CAT rating matter for battery-powered boards?
Less, because those circuits are not connected to mains. It matters the moment the same meter is used on anything plugged into an outlet.
Can I trust a CAT rating printed on a budget meter?
Not by itself. Fluke says test tools should be independently evaluated and certified by labs such as CSA, UL, TÜV or Intertek (ETL); look for one of those marks and check the listing with the certifier.[2]
What standard covers multimeter safety?
IEC 61010-2-033. Its third edition, published in 2023, covers hand-held multimeters for domestic and professional use that can measure mains voltage.[5]
Do test leads need a CAT rating too?
Check them as well: use leads marked for at least the same category and voltage as your measurement, and replace any with damaged insulation.