The Pollution Degree Rating of Power Meters and Split-Core Current Sensors

What is Pollution Degree?

In my opinion pollution degree is somewhat of a misnomer.  It’s a classification that relates to the quantity of condensation and dry pollution that exists in the environment.  If a split-core current sensor or split-core current transducer is rated for a particular pollution degree, it’s guaranteed to operate in a certain type of environment.

Pollution Degree affects not only the creepage distances but also the clearance necessary for safe use of the product. According to safety standards and certification bodies, offices and laboratories are degree 2 environments. Inside any sealed components or within air tight or water tight enclosures is considered degree 1, whilst harsher environments, typically those within industrial manufacturing enclosures is degree 3. In some ways, the pollution degree is similar to the IP rating system, but IP ratings don’t specify clearance distances for safety.

The Underwriters Laboratories (UL), IEC [1] and other safety standard bodies classify pollution degrees as follows:

Why is pollution degree important?

UL, IEC and other safety standards, stipulate that there should be appropriate distances maintained between high voltage and safety, low voltage signals. These distances are to ensure operator safety and depend on the risk of a voltage arc.  As you know, the risk of an arc increases when material, aka pollution, connects two conductors. A comparison of the distances required between high and low voltage signals in relation to pollution degrees 1 and 2 environments is shown in the table below:

Note:
1. Creepage distance is greater than clearance distance.
2. Creepage distance for degree 2 is 2 to 4 times longer than for degree 1.

What effect does this information have on current sensors and power meters?

Because humidity is often present in monitoring environments, whether or not a meter and its CTs can be used outdoor can be determined by the pollution degree rating.
Connectivity is a key area where pollution degree has an impact. For example, one vital distance is that between the ground shield and any voltage conductors, which can be as little as 1.6mm. Looking at table 2 this distance meets the safety standard for pollution degree 1 and for pollution degree 2 environments at 150 volts. In the case of 300-volt operation the connector only meets safety standards when used in a pollution degree 1 environment. Therefore, some voltage connectors above 150 volts do not meet the appropriate safety standards and are therefore considered to be unsafe.

To create a safe, non-hazardous test system it is important to understand the effects that pollution degree might have on your designs.

Definitions

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

Creepage Distance: The smallest distance between 2 conductive parts. This is measured along the face of the insulating matter.

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