What are Measurement Categories (CAT I, CAT II, Cat III, Cat IV)?

The IEC61010-1 defines categories for rating the safety of electrical testing instruments. The higher the category (CAT), the closer the equipment being tested can be to the utility power source. A meter can have multiple category ratings. Measurement Categories are also 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 is that a high voltage can overload a circuit and cause electrical and physical damage. Electrical test & measurement tools are assigned to 4 different designations; CAT I, CAT II, CAT III, and CAT IV. Tools that interact with electricity are designed for specific applications and conditions. Exceeding or deviating from application parameter can lead to inaccurate measurements or injury. For J&D Products, we will only be dealing with Categories III and IV.

Measurement Category III
This category refers to measurements on hard-wired equipment in fixed installations, distribution boards, and circuit breakers. Other examples are wiring, including cables, bus bars, junction boxes, switches, single-phase socket outlets in the fixed installation and stationary motors with permanent connections to fixed installations.

Measurement Category IV
This category refers to origin of installation or utility level measurements on primary over-current protection devices and on ripple control units. Used on utility three-phase circuits and outdoor conductors.

Module with Category III or IV circuits.

Rated Voltage IEC61010-1 2nd Edition UL61010B-1 (UL 31111-1)
300V 6,000V 4,000V 2,500V 4,000V 2,500V 1,500V
600V 8,000V 6,000V 4,500V 6,000V 4,500V 2,500V
1,000V 12,000V 8,000V 6,500V 8,000V 6,500V 4,500V
Resistance 2 ohms 2 ohms 12 ohms 2 ohms 12 ohms 30 ohms

What is “Pollution Degree”?

Pollution degree is a classification according to the amount of dry pollution and condensation present in the environment. This classification is important since it affects creep age and clearance distances required to insure the safety of a product. Office and laboratory areas are considered pollution degree 2 environments according to safety standards and certification bodies. Pollution degree 1 may be considered inside sealed components and within air/water tight enclosures. Pollution degree 3 is a harsher environment typical in many industrial manufacturing areas. Safety standards bodies such as Underwriters Laboratories (UL) and IEC [1] categorize them as follows: Pollution Degree 1: No pollution or only dry, nonconductive pollution occurs. The pollution has no effect. Pollution Degree 2: Normally only nonconductive pollution occurs. Temporary conductivity caused by condensation is to be expected. Pollution Degree 3: Conductive pollution or dry nonconductive pollution that becomes conductive due to condensation occurs. To be found in industrial environment or construction sites (harsh environments). Pollution Degree 4: The pollution generates persistent conductivity caused by conductive dust, rain, or snow. See table 1 for examples of each of these environments [2,3].

Pollution Degree 1 Pollution Degree 2 Pollution Degree 3 Pollution Degree 4
Clean Room environments Equipment being evaluated to 60950 Electrical equipment in industrial and farming areas Electrical equipment for outdoor use
Inside of sealed components Laboratories Unheated rooms
Test stations Boiler room
Office environment

Table 1. Examples of pollution degree environments

Clearly, ATE environments (i.e. Test Stations) are categorized as “Pollution Degree 2”. Any equipment designed for, or placed in a test station environment should have a pollution degree 2 rating in order to meet recognized safety standards.<