Analysis of some basic parameters of safety distance technology in PCB production

by:A-TECH      2021-03-12
PCB safety distance PCB safety distance includes electrical clearance (spatial distance), creepage distance (creepage distance) and insulation penetration distance. Electric clearance: the shortest distance measured along the air between two adjacent conductors or a conductor and the surface of the adjacent motor casing. Creepage distance: The shortest distance between two adjacent conductors or one conductor and the surface of the adjacent motor casing measured along the insulating surface. Insulation penetration distance: refers to the thickness of the insulation. Working voltage refers to the highest voltage that can be withstood on a special insulation component or when the equipment is working normally under the rated voltage. Determination of electrical clearance: According to the measured working voltage and insulation level, the distance can be determined. Normally: Primary AC part: L—N ≥ 2.5mm before the fuse, LN PE (earth) ≥ 2.5mm, after the fuse device, no requirement is required. But keep a certain distance as much as possible to avoid short circuit damage to the power supply. Primary side AC to DC part ≥2.0mm, primary side DC ground to earth ≥2.5mm (primary side floating ground to earth), primary side part to secondary side part ≥4.0mm, across components between the primary and secondary sides The electric gap of the secondary side part is ≥0.5mm, and the secondary side ground to the earth ≥1.0mm is enough. The distance is confirmed as the worst case, and the spatial distance still meets the regulations. Determination of creepage distance: According to the working voltage and insulation level, the creepage distance can be determined by looking up the table. But usually: primary side AC part: L—N ≥ 2.5mm before the fuse, LN earth ≥ 2.5mm, after the fuse, no requirement is required. But try to keep a certain distance to avoid short-circuit damage to the power supply. Primary side AC to DC part ≥2.0mm, primary side DC ground to ground ≥4.0mm, such as primary side ground to earth, primary side to secondary side ≥6.4mm, such as optocoupler, Y capacitor and other component parts with pin spacing ≤6.4mm Slotted. The distance between the secondary side parts is ≥0.5mm, that is, the secondary side ground to the earth ≥2.0mm or more. The insulation penetration distance between the two transformer stages is ≥8.0mm or more: According to the working voltage and insulation application, the following regulations should be met: More than 50V (71V AC peak or DC value), there is no thickness requirement; the minimum thickness of additional insulation should be 0.4mm; when the reinforced insulation does not withstand any mechanical stress that may cause deformation or performance degradation of the insulation material at normal temperature, The minimum thickness of the reinforced insulation should be 0.4mm. If the insulation provided is used in the protective enclosure of the equipment and will not be bumped or scratched during maintenance by the operator, and falls under any of the following conditions, the above requirements do not apply to thin-layer insulation materials regardless of their thickness For additional insulation, use at least two layers of materials, each of which can pass the electrical strength test for additional insulation; or additional insulation composed of three layers of materials, where any combination of two layers of materials can pass the additional insulation The electric strength test. For reinforced insulation, use at least two layers of materials, each of which can pass the electrical strength test for reinforced insulation; or reinforced insulation composed of three layers of insulating materials, where any combination of two layers of materials can pass the reinforced insulation The electric strength test. Wiring process precautions: Flat-mounted components such as capacitors must be flat-mounted without dispensing. For example, the distance between two conductors can be shortened by applying a force of 10N. When the distance is less than the safety distance requirement, glue can be used to fix this part to ensure its electrical clearance. When laying PVC film in some enclosure equipment, pay attention to ensuring the safety distance (pay attention to the processing technology). Be careful not to make any foreign objects such as glue wires on the PCB board. When processing parts, it should not cause insulation damage. Requirements related to flame-proof materials: Heat shrinkable tubing V-1 or more than VTM-2, VC tubing V-1 or more than VTM-2, Teflon tubing V-1 or more than VTM-2; plastic material such as silicone sheet, insulation Adhesive tape V-1 or VTM-2 or above, PCB board 94V-1 or above, is related to insulation class: working insulation: insulation required for normal operation of the equipment. Basic insulation: insulation providing basic protection against electric shock. Additional insulation: applied in addition to basic insulation Independent insulation to protect against electric shock in the event of basic insulation failure. Double insulation: insulation reinforced insulation composed of basic insulation plus additional insulation: a single insulation structure, under the conditions specified in this standard, all The level of protection provided against electric shock is equivalent to double insulation.
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