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Safety requirements between PCBA board and shell
2021-09-28
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Author:Frank

Safety requirements between PCBA board and shell
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.
1. The decision of electrical clearance:
According to the measured working voltage and insulation level, the distance can be determined. The clearance size requirements of the primary side circuit are shown in Table 3 and Table 4 The clearance size requirements of the secondary side circuit are shown in Table 5
But usually: primary AC part: L—N≥2.5mm before the fuse, L.N PE (earth)≥2.5mm, after the fuse is installed, it is not required, but a certain distance should be kept as far as possible to avoid short-circuit damage to the power supply.

pcb board

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, the gap gap of the secondary side part of the components connected between the primary and secondary sides ≥ 0.5mm is enough for secondary ground to earth ≥1.0mm

Note: Before deciding whether to meet the requirements, the internal parts should be applied with a force of 10N, and the outer shell should be applied with a force of 30N to reduce the distance, so that the space distance still meets the requirements in the worst case.


2. Determination of creepage distance:

According to the working voltage and insulation level, check the table 6 to determine the creepage distance

But usually:

(1) Primary AC part: L—N≥2.5mm before the fuse, L.N 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.

(2), the primary side AC to DC part ≥2.0mm

(3), primary side direct current ground to ground≥4.0mm, such as primary side ground to ground

(4), the primary side to the secondary side ≥6.4mm, such as optocoupler, Y capacitor and other components of the foot spacing of ≤6.4mm should be slotted.

(5) ≥0.5mm between the secondary side parts is enough

(6), the secondary side ground to the ground ≥ 2.0mm or more

(7) Between the two stages of the transformer ≥8.0mm


3. Insulation penetration distance:

According to the working voltage and insulation application, the following regulations should be met:

——The working voltage does not exceed 50V (71V AC peak value or DC value), and 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 insulating material under 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 supplementary insulation, use at least two layers of materials, each of which can pass the electrical strength test for supplementary insulation; or:

——Additional insulation composed of three layers of materials, of which any combination of two layers of materials can pass the electrical strength test of the additional insulation; or:

-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, of which any combination of two layers of materials can pass the electrical strength test of the reinforced insulation.
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