PCB News - Detailed explanation of PCB safety distance in PCB design

The safety distance includes electrical clearance (spatial distance), creepage distance (creepage distance) and insulation penetration distance.

Electric gap: 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 a conductor and the surface of the adjacent motor casing measured along the insulating surface.

Determination of clearance:

According to the measured working voltage and insulation level, the distance can be determined

The electrical clearance size requirements of the primary side circuit are shown in Table 3 and Table 4

The requirements for the clearance size of the secondary side circuit are shown in Table 5

But usually: primary side AC part: L-N≥2.5mm before the fuse, L.N PE (earth)≥2.5mm, after the fuse is not required, but as far as possible 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 earth ≥2.5mm (primary floating ground to earth)

The part between the primary side and the secondary side is ≥4.0mm, which is connected to the components between the primary and secondary sides

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

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 in the worst case, the space distance still meets the requirements.

Creepage distance determination:

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

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), primary side AC to DC part ≥2.0mm

(3), primary side DC 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), ≥0.5mm between the secondary side part is enough

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

(7), between two stages of transformer ≥8.0mm

Insulation penetration distance:

According to the working voltage and insulation application, the following requirements shall 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 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 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, any combination of two layers of materials can pass the electrical strength test of reinforced insulation.

There are some points to note about the wiring process:

Flat-mounted components such as capacitors must be mounted flat without dispensing.

If the distance between two conductors can be shortened by applying a force of 10N, when the distance is less than the safety distance requirement, this part can be fixed by glue to ensure its electrical clearance.

When paving PVC film in some enclosure equipment, pay attention to ensuring the safety distance (pay attention to the processing technology).

Parts are glued and fixed. 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.

There are requirements for flameproof materials:

Heat shrinkable tubing V-1 or more than VTM-2 VC casing V-1 or more than VTM-2

Teflon casing V-1 or more than VTM-2; plastic materials such as silicone sheet, insulating tape V-1 or more than VTM-2

PCB board94V-1 above

About the insulation class

(1), work insulation: the insulation required for the normal operation of the equipment

(2) Basic insulation: insulation that provides basic protection against electric shock

(3). Additional insulation: independent insulation applied in addition to basic insulation to protect against electric shock once the basic insulation fails

(4), double insulation: insulation composed of basic insulation plus additional insulation

(5), reinforced insulation: a single insulation structure, under the conditions specified in this standard, the protection level it provides against electric shock is equivalent to double insulation

The above is the introduction of PCB safety distance detailed explanation in PCB design. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology.