The clearance distance depends upon the Rated impulse withstand Voltage Uimp. The Uimp for NSX/CVS is 8 kV. Based on the IEC61439-1,
Table 1, the minimum clearance distance for 8kV Impulse voltage is 8mm respectively. The bus bar clearance in Blockset column maintained is ≥ 8mm
where NSX/CVS used. The line side clearance of NSX/CVS breaker will be ≥ 14mm.
IEC 61439-1 standard defines the requirements applicable to clearances inside a switchboard. These requirements are based on the principles of
IEC 60664-1 standard and enable the coordination of clearance inside the switchboard. They guarantee the use of mains over-voltages due to
control apparatus or atmospheric conditions such as lightning impacts. Clearance is the shortest distance in the air:
• between two live conductors,
• between a live conductor and the ground.
The standard provides a table giving the minimum clearance to comply with in order to observe the rated impulse withstand voltage Uimp declared by
the manufacturer for a circuit. The values given in the table are established according to non- homogeneous electrical fields and a pollution degree of
3 (the most unfavorable conditions). These ensure that impulse voltages can be withstood in an altitude range of 0 to 2000 m.
The creepage distance depends upon the Rated Insulating Voltage Ui and the insulation material group. The insulating voltage of NSX/CVS is 750V.
Based on the IEC61439-1, Table 2, the minimum creepage distance for 800V is 12.5mm. The creepage distance for BlockSeT column maintained is ≥ 12.5mm
where NSX/CVS used.
IEC 61439-1 standard defines the requirements applicable to creepage distances inside a switchboard. These requirements are based on the principles of
IEC 60664-1 standard and enable the coordination of clearance inside the switchboard. They ensure that the ageing of insulating materials and environmental
pollution have been taken into account in the electrical switchboard's operation. The creepage distance is the shortest distance along the surface of an insulation between:
• two live conductors,
• between a live conductor and the bounding surface.
