UL, CSA and VDE safety standards emphasize the safety requirements for creepage distances, which are designed to prevent ignition between devices or between devices and ground, thereby threatening personal safety.
The insulator creepage distance is the shortest distance or the sum of the shortest distances along the insulating surface between two parts of the insulator that normally carry the operating voltage.
Classification
Crawling means, can be regarded as an ant from an electrically charged body to walk to another electrically charged body must go through the shortest distance, is the creepage distance. The electrical gap, is the shortest distance an ant with wings, flies.
The national standard has specific provisions, different shapes of insulation, creepage distance calculation method is different.
In GB/T 2900.18-2008 electrical terminology standards for creepage distance has this definition: creepage distance is the shortest distance between the two conductive parts along the surface of the solid insulating material.
Safety distance includes electrical clearance (space distance), creepage distance (distance along the surface) and insulation penetration distance.
1, electrical clearance
The shortest distance measured along the air between two adjacent conductors or one conductor and the surface of the adjacent motor casing.
2, creepage distance
Two adjacent conductors or a conductor and the adjacent motor casing surface of the shortest distance measured along the insulating surface.
Determination of the electrical clearance:
Based on the measured operating voltage and insulation level, you can decide the distance
But usually: primary side AC part: before the fuse L-N ≥ 2.5mm, L.N PE (earth) ≥ 2.5mm, the fuse device can not be done after the requirements, but as far as possible to maintain a certain distance to avoid Short-circuit damage to the power supply.
Primary AC to DC part ≥ 2.0mm;
Primary DC ground to earth ≥ 2.5mm (primary floating ground to earth);
Primary to secondary part of the part ≥ 4.0mm, spanning between the primary and secondary side of the components;
Secondary part of the electrical gap ≥ 0.5mm can be;
Secondary side ground to earth ≥ 1.0mm can be.
Note: Before deciding whether or not to meet the requirements, the internal parts should be applied to 10N force, the shell applied to 30N force, in order to reduce the distance, so that the worst case scenario is confirmed, the space distance is still in line with the provisions.
3, insulation penetration distance
Should be based on the operating voltage and insulation applications in line with the following provisions:
- for operating voltage does not exceed 50V (71V AC peak or DC value), no thickness requirements;
- -The minimum thickness of the additional insulation shall be 0.4 mm;
- When the reinforced insulation is not subjected to any mechanical stress that may cause deformation or degradation of the insulation at normal temperatures, the minimum thickness of the reinforced insulation shall be 0.4 mm.
The above requirements do not apply to thin layers of insulation irrespective of their thickness if the insulation provided is to be used within the protective enclosure of the equipment and is not subject to knocks or abrasions when maintained by the operator and is of any of the following types;
--For additional insulation, a minimum of two layers of material are used, where each layer of the material is capable of passing the electrical strength test for additional insulation; or:
-- For additional insulation consisting of three layers of material, any combination of two of which is capable of passing the electrical strength test for additional insulation;
-- For reinforced insulation, using at least two layers of material, each of which is capable of passing the electrical strength test for reinforced insulation