PCB Tech - Safety distance requirements between PCBA board and shell

Safety distance requirements between PCBA board and shell

The safety distance between the PCBA board and the enclosure includes electrical clearance (spatial distance), creepage distance (creepage distance) and insulation penetration distance.

1. Requirements for electrical clearance between PCBA board and housing:

The electrical clearance refers to the shortest distance measured along the air between two adjacent conductors or a conductor and the surface of the adjacent motor casing.

The distance can be determined according to the measured working voltage and insulation level, but usually:

1) Primary AC part: L-N≥2.5mm before the fuse, L.N PE (earth)≥2.5mm, no requirement is required after the fuse is installed, but a certain distance should be kept as far as possible to avoid short-circuit damage to the power supply.

2) The AC to DC part of the primary side is ≥2.0mm.

3) Primary side DC ground to ground ≥ 2.5mm (primary side floating ground to ground).

4) The primary-side part to the secondary-side part ≥ 4.0mm, which bridges the components between the primary and secondary sides.

5) The electric gap of the secondary side part is ≥0.5mm.

6) The secondary side ground to the earth ≥1.0mm is enough.

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. Creepage distance requirements between PCBA board and shell:

Creepage distance refers to the shortest distance measured along the insulating surface between two adjacent conductors or a conductor and the surface of the adjacent motor casing.

According to the working voltage and insulation level, the creepage distance can be determined, but usually:

1) Primary side AC part: L-N≥2.5mm before the fuse, L.N earth ≥2.5mm, after the fuse, there is no requirement, but try to keep a certain distance to avoid short-circuit damage to the power supply.

2) The AC to DC part of the primary side is ≥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 optocouplers, Y capacitors and other components, the foot spacing of ≤6.4mm should be slotted.

5) The distance between the secondary side parts is ≥0.5mm.

6) The secondary side ground to the earth ≥ 2.0mm or more.

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

3. Requirements for insulation penetration distance between circuit board and shell:

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

1) The working voltage does not exceed 50V (71V AC peak value or DC value), and there is no thickness requirement.

2) The minimum thickness of additional insulation should be 0.4mm.

3) 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 ;

1) For additional insulation, use at least two layers of materials, each of which can pass the electrical strength test for additional insulation;

2) 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;

3) For reinforced insulation, use at least two layers of materials, each of which can pass the electrical strength test for reinforced insulation;

4) 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.