How to read a CAT multimeter rating: understanding and use for testing maximum voltage

Content

What is the CAT rating of a multimeter?
Different categories and their definitions
How the CAT multimeter rating system works
An example of using the CAT multimeter rating system

Multimeters and other electrical test equipment are often assigned a category rating. This is to give the user an idea of the maximum voltage the device can safely measure. These ratings are presented as CAT I, CAT II, CAT III, or CAT IV. Each rating indicates the maximum safe voltage to measure.

What is the CAT rating of a multimeter?

Category Rating (CAT) is a system used by manufacturers to determine the level of protection provided by electrical equipment when measuring voltage. Ratings range from CAT I to CAT IV depending on the type of voltage being measured.

When should I use a different category meter? The answer depends on the work being done.

Multimeters are commonly used in mains and low voltage applications. For example, measuring an outlet or testing a light bulb. In these cases, CAT I or CAT II meters will most likely suffice. However, when operating in higher voltage environments, such as a circuit breaker panel, you may need additional surge protection than what a standard meter can provide. Here you can consider using a newer, higher rated multimeter.

Different categories and their definitions

When trying to measure load, there are 4 accepted levels of measurement.

CAT I: This is commonly used in metering circuits that are directly connected to the building's electrical wiring system. Examples include non-current-carrying components such as lamps, switches, circuit breakers, etc. Electric shock is unlikely or impossible under such conditions.

LETTER XNUMX: This category is used in environments where the transients are only slightly above normal voltage. Examples include sockets, switches, junction boxes, etc. Electric shock is unlikely or unlikely to occur in these environments.

CAT III: This category is used for measurements taken close to the power source, such as on utility panels and switchboards in buildings or industrial facilities. Electric shock is highly unlikely under these conditions. However, they can occur with a low probability due to a malfunction. (1)

Category IV: Instruments included in this category are used on the primary side of an isolating transformer with reinforced insulation and for measurements on power lines laid outside buildings (overhead lines, cables).

The International Electrotechnical Commission (IEC) has developed four levels of electric and magnetic field strengths with transient test recommendations for each.

Features	CAT I	CAT II	CAT III	LETTER XNUMX
Working voltage	150V	150V	150V	150V
300V	300V	300V	300V
600V	600V	600V	600V
1000V	1000V	1000V	1000V
Transient voltage	800V	1500V	2500V	4000V
1500V	2500V	4000V	6000V
2500V	4000V	6000V	8000V
4000V	6000V	8000V	12000V
Test source (impedance)	30 ohm	12 ohm	2 ohm	2 ohm
30 ohm	12 ohm	2 ohm	2 ohm
30 ohm	12 ohm	2 ohm	2 ohm
30 ohm	12 ohm	2 ohm	2 ohm
Operating current	5A	12.5A	75A	75A
10A	25A	150A	150A
20A	50A	300A	300A
33.3A	83.3A	500A	500A
Transient current	26.6A	125A	1250A	2000A
50A	208.3A	2000A	3000A
83.3A	333.3A	3000A	4000A
133.3A	500A	4000A	6000A

How the CAT multimeter rating system works

The most commonly used multimeters on the market fall into two categories: CAT I and CAT III. A CAT I multimeter is used to measure voltage up to 600V, while a CAT III multimeter is used up to 1000V. Anything above that requires an even higher grade, such as CAT II and IV, designed for 10,000V and 20,000V respectively.

An example of using the CAT multimeter rating system

Imagine that you are looking at the electrical panel of your house. You need to check several wires. The wires are connected directly to the main power line (240 Volts). Touching them by mistake could result in serious injury or death. To safely take measurements in this situation, you will need a higher grade multimeter (CAT II or better) that will protect you and your equipment from damage caused by high energy levels. (2)

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