Creepage and clearance distances

To protect persons or system from the effects of electrical operating voltages, especially in the case of malfunction of equipment, sufficient measurement of the clearance and creepage distance is required.

For safety reasons and for every certification (IEC, UL, CSA) it is essential that certain clearance and creepage distances are maintained. In the following you find further explanations and information on determining clearance and creepage distances.

Clearance distance - shortest separation in the air between two conducting parts

Determination in accordance with IEC:Identification of the overvoltage category
Definition of the pollution severity
Determination of the rated surge voltage according to table 1 in the brochure below
Determination of the minimum creepage distance according to table 2 in the brochure below

Creepage distance - shortest separation along the surface of an insulating material between two conducting parts

Determination in accordance with IEC:

Identification of the overvoltage category
Definition of the pollution severity
Determination of the rated surge voltage dependent on the mains according to table 3 in the brochure below
Determination of the minimum creepage distance dependent on the pollution severity according to table 4 in the brochure below

The rated impulse voltage, critical for the dimensioning of the clearance distance, results from the overvoltage category and the conductor - earth voltage derived from the nominal mains voltage (taking all mains types into consideration).

The minimum clearance distance (up to installation heights of 2000 m above sea level) is determined from the rated surge voltage and the pollution severity.

A detailed overview of the calculation of the clearance and creepage distance is available as a download.

Overvoltage category and pollution degree

Overvoltage categories

Developers of electrical devices determine how robust or sensitive the electrical device will be against overvoltage peaks based on the electrical components selected, the conductor cross-sections, the clearance and creepage distances between the components, the insulating materials, etc.

The electrical device is assigned to one of the 4 overvoltage categories (I - IV) described in the DIN EN 60664-1 VDE 0110-1 standard. Electrical devices in overvoltage category I can withstand lower overvoltages than electrical devices in overvoltage category IV.

Degree of pollution

Any kind of solid, liquid or gaseous foreign substance that reduces the electrical strength or surface resistance of the insulation is considered to be pollution. The pollution or the expected pollution affecting electrical equipment in the application is described and defined as a degree of pollution (1 - 4) in the standard DIN EN 60664-1 VDE 0110-1. The pollution degree is the numerical value that indicates the expected pollution of the environment – the lower the value, the lower the expected pollution. The pollution degree is a parameter for dimensioning the clearance and creepage distances of electrical equipment.

Pollution degree 1: none or only slight, non-conductive pollution. The contamination has no influence.
Pollution degree 2: non-conductive pollution which can become conductive due to occasional condensation (dew) or e.g., hand perspiration.
Pollution degree 3: Pollution that is conductive or can become conductive through condensation.
Pollution degree 4: conductive dust, rain or wetness.