To protect persons or systems from the effects of electrical operating voltages, especially in the case of equipment malfunctions, 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
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.
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