What are Multimeter CAT (Category) Safety Ratings?

If you’ve ever used a multimeter before, or looked at a datasheet for one, you’ve likely noticed a CAT (category) safety rating. What is that and why is it important? This blog and corresponding video will cover those questions.

According to the IEC (International Electrotechnical Commission), multimeter manufacturers must follow the safety testing guidelines for all of their products to ensure that each device meets or exceeds the rating required. These measures are put in place to protect the user from unintentional shock, potentially resulting in death.

There are four levels defined by the type of load to be measured.

CAT I

Electronic Devices
Anything from a small circuit board to larger device with high-voltage but low-energy
CAT II
Single-Phase AC Loads
Appliances or portable tools
CAT III
Three-Phase Distribution
Some large building lighting systems and polyphase motors
CAT IV
Three-Phase Utility Connections or Outdoor Conductors
Electrical meters, outdoor connections, any low-voltage and high-energy connection

Within these four levels, the IEC has setup transient test guidelines for each category.

Measurement Category Working Voltage Transient Voltage Test Source (Impedance)
CAT I 150 V 800 V 30 Ohms
CAT I 300 V 1500 V 30 Ohms
CAT I 600 V 2500 V 30 Ohms
CAT I 1000 V 4000 V 30 Ohms
CAT II 150 V 1500 V 12 Ohms
CAT II 300 V 2500 V 12 Ohms
CAT II 600 V 4000 V 12 Ohms
CAT II 1000 V 6000 V 12 Ohms
CAT III 150 V 2500 V 2 Ohms
CAT III 300 V 4000 V 2 Ohms
CAT III 600 V 6000 V 2 Ohms
CAT III 1000 V 8000 V 2 Ohms
CAT IV 150 V 4000 V 2 Ohms
CAT IV 300 V 6000 V 2 Ohms
CAT IV 600 V 8000 V 2 Ohms
CAT IV 1000 V 12000 V 2 Ohms

If we extend this to calculate the current for the working and transient voltages, you’ll see that even though two CAT ratings cover the same working voltage, that does NOT mean they are an equal.

Measurement Category Working Voltage Transient Voltage Test Source (Impedance) Working Current Transient Current
CAT I 150V 800V 30 Ohms 5A 26.6A
CAT I 300V 1500V 30 Ohms 10A 50A
CAT I 600V 2500V 30 Ohms 20A 83.3A
CAT I 1000V 4000V 30 Ohms 33.3A 133.3A
CAT II 150V 1500V 12 Ohms 12.5A 125A
CAT II 300V 2500V 12 Ohms 25A 208.3A
CAT II 600V 4000V 12 Ohms 50A 333.3A
CAT II 1000V 6000V 12 Ohms 83.3A 500A
CAT III 150V 2500V 2 Ohms 75A 1250A
CAT III 300V 4000V 2 Ohms 150A 2000A
CAT III 600V 6000V 2 Ohms 300A 3000A
CAT III 1000V 8000V 2 Ohms 500A 4000A
CAT IV 150V 4000V 2 Ohms 75A 2000A
CAT IV 300V 6000V 2 Ohms 150A 3000A
CAT IV 600V 8000V 2 Ohms 300A 4000A
CAT IV 1000V 12000V 2 Ohms 500A 6000A

Now using CAT III at 600V and CAT II at 1000V as an example clearly displays how just because the rated working voltage is higher, does NOT mean that it can handle as much overall.

There is no sure way to know what rating a meter is without finding the CAT rating either on the unit itself or on the multimeter’s datasheet. Remember, when in doubt, more protection is always better.

About this author

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Ashley Awalt is a Technical Content Developer that has been with Digi-Key Electronics since 2011. She earned her Associate of Applied Science degree in Electronics Technology & Automated Systems from Northland Community & Technical College through the Digi-Key scholarship program. Her current role is to assist in creating unique technical projects, documenting the process and ultimately participating in the production of video media coverage for the projects. In her spare time, Ashley likes to – oh, wait, is there such a thing as spare time when you’re a mom?

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