Measurement Categories CAT I, CAT II, CAT III, CAT IV

Tuesday, 06/12/2022, 20:22

What are electrical measurement categories CAT I, CAT II, CAT III, CAT IV ?


Measurement Categories CAT I, CAT II, CAT III, CAT IV are used to rate test instruments on their ability to resist a voltage spike, which is applied through a specific resistance. The higher the category, the more risk there that a high voltage can overload a circuit and cause electrical and physical damage. Usually, the higher the CAT (category) rating, the safer the rating.
Before looking into the various categories it’s important to understand exactly why tools are certified in particular ways. First off, when dealing with electricity, you MUST understand that the tool is either designed for a particular application or not. Many people don’t stop and think what would happen if the test probes, for example, don’t have enough insulation and too much voltage is applied to them, causing an arc. Or if too much current passes through the meter, causing it to more or less explode. These aren’t just imaginations, each one of these events has happened time and time again to electricians and amateurs alike who decided to use improper equipment to test and measure current and voltage. With that said, let’s take a closer look at the four primary measurement categories for electrical tools.


This category is for measurements of voltages from specially protected secondary circuits. Such voltage measurements include signal levels, special equipment, limited-energy parts of equipment, circuits powered by regulated low-voltage sources, and electronics. These categories of use present very little chance for danger or overloading on any significant level.


This is sufficient for a receptacle outlet circuit or plug-in loads, also referred to as “local-level electrical distribution”. This would also include measurements performed on household appliances, portable tools, and similar modules.


Distribution wiring are qualified for this group, including “mains” bus, feeders and branch circuits. Also, permanently installed or “hard-wired” loads and distribution boards. Other examples are higher voltage wiring, including power cables, bus bars, junction boxes, switches, and stationary motors with permanent connections to fixed installations


This is “Origin of installation” or utility level applications such as any outside cable run. This category refers to measurements on primary over-current protection devices and on ripple control units.


Using the chart below we deduce the following: This specification informs the user this module is rated for 300V CAT II and 600V CAT I. In other words, this module can withstand up to 2,500V impulse voltage. This specification additionally informs the user this module must not be connected to MAINs CAT II circuits when operated above 300V. Lastly, the user should not use this module with Category III or IV circuits.


Rated Voltage IEC 61010-1
2nd Edition
UL 61010B-1
(UL 31111-1)
150 V 4000 V   2500 V 1500 V 2500 V  1500 V  800 V  
300 V 6000 V  4000 V  2500 V 4000 V  2500 V  1500 V  
 600 V  8000 V  6000 V  4000 V  6000 V  4000 V  2500 V  
 1000 V  12 kV  8000 V  6000 V  8000 V  6000 V  4000 V  
 Resistance  2 ohms  2 ohms 12 ohms 2 ohms 12 ohms 30 ohms  


Other news

Lightning rod is a common name used to refer to a system installed on the top of a building or on a high pole, consisting of one or more metal rods with pointed ends connected to ground conductors for protection. for structures, buildings and objects below from being struck by lightning.
The surge protection selection must be done following the local electrical code requirements (e.g. : minimum rating for In) and specific conditions (e.g. : high lightning density).
Surge surge protection devices (SPDs), also known as surge suppressors, are specific products in the electrical industry, the specifications of lightning protection devices on documents or products displayed Displays symbols and parameters to describe their own properties. Based on these parameters we can understand and compare the technical features of the devices, in order to use them most effectively.
Lightning protection involves using technical measures and systems to protect people, property, and infrastructure from the harmful effects of lightning. This system helps minimize the risk of damage caused by direct lightning strikes or induced surges.
Different electrical networks have different specifications and connections, so manufacturers have designed products for their respective protection installations. If selected incorrectly and installed improperly, not only will it lose its effectiveness, but it can also cause damage, fire, loss of electrical safety and affect the entire system.
Brazilian researchers captured on camera the moment when lightning rods on buildings released an upward discharge to attract incoming lightning.
Some standards on Lightning Protection, Earthing of International (IEC, IEEC), Vietnam and other countries (France, Spain, US, British ..)
What is the resistivity of the earth? The resistance of a cube earth is 1m3, to the current flowing from one side of the earth block to the opposite face. The unit of resistivity of soil is Ωm (ohm meter). It is possible to measure resistivity of soil according to the Wenner or Schlumberger method.
Sử dụng Type của thiết bị chống sét như thế nào ? Các thiết bị chống sét thuộc nhóm hay Type được các nhà sản xuất quy định trên mỗi sản phẩm, chúng phải đáp ứng theo các yêu cầu thử nghiệm của tiêu chuẩn IEC. Vậy khi nào thì sử dụng type 1, type 2 hay type 3, sử dụng như thế nào là phù hợp ?
Sét là một hiện tượng khí tượng phức tạp. Nắm rõ được bản chất quá trình hình thành và tác động của sét đến các công trình xây dựng, ví dụ như các tòa nhà, kho tàng, bến bãi, các cột, tháp vô tuyến, phát thanh truyền hình, các đường dây điện lực, đường dây viễn thông, đường dây điện thoại, internet, cáp đồng trục anten phi đơ từ đó ta có các biện pháp phòng chống sét một cách có hiệu quả. Vậy sét là gì ?