Safe Distance

This Gold Phoenix PCB Knowledge Center article explains safe distance requirements in PCB design, including electrical clearance (space distance), creepage distance (distance along the surface) and insulation penetration distance.

1. Electrical Clearance

Electrical clearance is the shortest distance between two adjacent conductors or between one conductor and the surface of an adjacent motor housing.

Determination of Electrical Clearance

The distance is determined based on the measured operating voltage and insulation level. Typical guidelines are as follows:

Primary (AC) side:

• L-N (before fuse): ≥ 2.5 mm

• L, N to PE (earth): ≥ 2.5 mm

• After fuse: no strict requirement, but maintain a certain distance to avoid short circuit damage to the power supply

Primary AC to DC part: ≥ 2.0 mm

DC side to earth: ≥ 2.5 mm (primary side floating grounding to earth)

Primary to secondary side: ≥ 4.0 mm. Cross-components connected between primary and secondary sides with an electrical clearance of ≥ 0.5 mm may be considered part of the secondary side.

Secondary to earth: ≥ 1.0 mm

Note: To verify whether requirements are met, internal parts should be tested with a 10 N force, and the enclosure with a 30 N force, to reduce the distance and confirm that in the worst case the space distance still complies with specifications.

2. Creepage Distance

Creepage distance is the shortest distance between two adjacent conductors or between one conductor and the surface of an adjacent motor housing along the insulated surface.

Determination of Creepage Distance

3. Insulation Penetration Distance

The following requirements shall be met according to the working voltage and the insulation application:

• Operating voltage ≤ 50 V (71 V AC peak or DC): no specific voltage requirement

• Additional insulation: minimum thickness of 0.4 mm

• Reinforced insulation: minimum thickness of 0.4 mm, provided that no mechanical stress may cause deformation or deterioration of the insulation at normal temperatures, and the insulation is provided in a protective enclosure

For additional insulation, use at least two layers of material, each of which can be tested by the electrical strength test of additional insulation; or use three layers of insulating material in which any combination of two layers can be tested by the electrical strength test.

For reinforced insulation, use at least two layers of material, each of which can be tested by the dielectric strength test of reinforced insulation; or use three layers of insulating material in which any combination of two layers can be tested by the dielectric strength test of reinforced insulation.

Wiring Process Notes

• Flat surface components such as capacitors must be mounted flat without adhesive dispensing

• If two conductors can be brought closer under a 10 N force to less than the safe distance requirement, adhesive dispensing can be used to fix parts and ensure electrical clearance

• When PVC film is used inside the enclosure, pay attention to safe distance requirements during processing

• When adhesive dispensing is used to fix parts, ensure no foreign bodies (such as silk) are present on the PCB board

• Insulation failures should not be caused during machining of parts

Flameproof Material Requirements

Insulation Levels

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