Articles & Blogs > What are Multimeter CAT (Category) Safety Ratings?

What are Multimeter CAT (Category) Safety Ratings?

By: Ashley Awalt 2020-02-25

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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

Ashley Awalt is a Technical Content Developer that has been with DigiKey since 2011. She earned her Associate of Applied Science degree in Electronics Technology & Automated Systems from Northland Community & Technical College through the DigiKey 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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