Sep. 02, 2019
Safety requirements between PCBA plate and shell shared by electric circuit board assembly manufacturer.
Safety distance includes electrical clearance (space distance), creepage distance (surface distance) and insulation penetration distance
Electrical clearance: the shortest distance measured along the air between two adjacent conductors or one conductor and the surface of an adjacent motor housing.
Creepage distance: the shortest distance measured along a perfectly insulated surface between two adjacent conductors or one conductor and an adjacent housing surface.
1. Determination of electrical clearance:
According to the measured working voltage and insulation level, the size requirements of the electrical gap of the primary side line can be determined. See table 3 and table 4 for the size requirements of the electrical gap of the secondary side line.
But usually: primary side ac part: before fuse l-n ≥2.5mm, l.npe (earth) ≥2.5mm, fuse installation after not required, but as far as possible to avoid short-circuit damage to the power supply.
Primary side ac to dc part ≥2.0mm
The dc ground to ground of the primary side shall be ≥2.5mm (the ground to ground of the primary side of the printed circuit board shall be ≥4.0mm), and the electric gap of the secondary side shall be ≥0.5mm for the components bonded between the primary and secondary sides, and the secondary ground shall be ≥1.0mm.
Note: before deciding whether to meet the requirements, the internal parts should be applied with 10N force and the shell with 30N force to reduce the distance, so that the space distance can still meet the requirements in the worst case.
2. Determination of creepage distance:
According to the working voltage and insulation grade of the printed circuit board assembly, the creepage distance can be determined by referring to table.
(1) primary side ac part: L -- N≥2.5mm before fuse, L.N earth ≥2.5mm, after fuse may not be required, but try to keep a certain distance to avoid short-circuit damage to the power supply.
(2) primary side ac to dc part ≥2.0mm
(3) primary side dc ground to ground ≥4.0mm such as secondary side to ground
(4) the primary side to the secondary side ≥6.4mm, such as optical coupler, Y capacitor and other elements, the pin spacing ≤6.4mm shall be grooved.
(5) ≥0.5mm between parts of the secondary side
(6) secondary ground to ground ≥2.0mm
(7) transformer interval ≥8.0mm