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
Creepage distance - shortest separation along the surface of an insulating material between two conducting parts
Determination in accordance with IEC:
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 categories
With the selection of the electrical components, the conductor cross-sections, the clearance and creepage distances between the components, the insulating materials, etc., the developers of electrical devices determine how robust or sensitive the electrical device is against overvoltage peaks.
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 overvoltage than Electrical devices in overvoltage category IV.
Pollution degree
Any kind of solid, liquid or gaseous foreign substances that reduces the electrical strength or surface resistance of the insulation is considered as pollution. In the standard DIN EN 60664-1 VDE 0110-1 the pollution or the expected pollution of the electrical equipment in the application is described and defined as pollution degree (1 - 4). The pollution degree is the numerical value that indicates the expected pollution of the environment, as lower the value as lower is the expected pollution. The pollution degree is a parameter for dimensioning the clearance and creepage distances of electrical equipment.
