Pollution Degree Rating for Electrical Equipment

Contents

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 creepage and clearance distances required to ensure 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].

 


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.

Why is pollution degree important to you?


Safety standards, such as UL and IEC, specify appropriate distances between high voltage and safety low voltage signals. These distances help to ensure operator safety and are dependent on environmental conditions, (i.e. pollution degree). Table 2 shows a comparison of the required distances between high and low voltage signals in a pollution degree 1 and pollution degree 2 environment.




Table 2. Affect of Pollution degree on safety distances

Note:
1. The creepage distance is much larger than the clearance distance.
2. The creepage distance for pollution degree 2 is 2 to 4 times longer than for pollution degree 1.

How does this information affect equipment design?


One key area where pollution degree has an impact is connectivity. D-subminiature (Dsub) connectors are commonly used in test equipment design. They are available from many vendors and are inexpensive. One critical distance is between the connector pin and the ground shield, which is about 1.6mm. Referring back to table 2, this distance meets safety standards for both pollution degree 1 and pollution degree 2 environments at 150 volts. For 300 volt operation, the connector meets safety standards ONLY if used in a pollution degree 1 environment. Therefore, within a typical test environment, using a Dsub connector above 150V does not meet applicable safety standards and is considered unsafe.

Understanding the effects of pollution degree on your designs will help to ensure that you are creating a safe, non-hazardous test system.

Definitions


Clearance: The shortest distance in air between two conductive parts.

Creepage Distance: The shortest distance along the surface of the insulating material between two conductive parts.

References


1. IEC 60664-1, Insulation coordination for equipment within low-voltage systems - Part 1: Principles, requirements and tests

2. DIN VDE 0110, Dimensions of the creepage distances, part 1 section 3.2

3. IEC 61010-1 (UL 61010-1, EN 61010-1), Safety requirements for electrical equipment for measurement, control and laboratory use - Part 1