PCB News - PCB design distance and related safety requirements

Distance and related safety requirements

1. Electric clearance: the shortest distance measured along the air between two adjacent conductors or a conductor and the surface of the adjacent motor casing.

2. 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.

Determination of electrical clearance:

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

Please refer to Table 3 and Table 4 for the requirements of the electrical gap size of the primary side circuit

See Table 5 for the requirements of the electrical gap size of the secondary side circuit

But usually: primary AC part: L-N≥2.5mm before the fuse, L.N-PE (earth)≥2.5mm, after the fuse is not required, but keep a certain distance as much as possible 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 primary side part to the secondary side part ≥4.0mm, the components that are connected between the primary and secondary sides

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

The secondary side ground to the ground ≥1.0mm suffices

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 regulations when it is confirmed as the worst.

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 side 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 optocouplers, Y capacitors 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 shall 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 shall 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.

4. There are some points to note about the wiring process:

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

For example, the distance between two conductors can be shortened by applying a force of 10N. When the distance is less than the safety distance requirement, glue can be used to fix this part to ensure its electrical clearance.

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

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.

5. There are requirements for anti-flammable materials:

Heat shrinkable tubing V-1 or more than VTM-2; PVC tubing V-1 or more than VTM-2

Teflon casing V-1 or VTM-2 or more; plastic material such as silicone sheet, insulating tape V-1 or VTM-2 or more PCB board 94V-1 or more

6. About the insulation level

(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 shocks 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 applicable situations of various insulations are as follows:

A. Operational insulation oprational insulation

a. Between two parts with different voltages

b. Between ELV circuit (or SELV circuit) and grounded conductive parts.

B, basic insulation basic insulation

a. Between parts with dangerous voltage and conductive parts that are grounded;

b. Between SELV circuits that have dangerous voltages and rely on grounding;

c. Between the power conductor on the primary side and the grounding shield or the core of the main power transformer;

d. As part of double insulation.

C, supplementary insulation supplementary insulation

a. Generally speaking, it is between the accessible conductor parts and the parts that may carry dangerous voltage after the basic insulation is damaged, such as:

1.. Between the appearance of handles, knobs, handles or the like and their ungrounded shafts.

2. Between the metal shell of the second type of equipment and the outer skin of the power cord passing through the shell.

3. Between the ELV circuit and the ungrounded metal shell.

b. As part of double insulation

D. Double insulation

Double insulation Reinforced insulation

Generally speaking, between the primary circuit and

a. Between accessible non-grounded conductive parts, or

b. Between floating SELV circuits or

c. Between TNV circuits

Double insulation = basic insulation + supplementary insulation

Note: ELV circuit: extra low voltage circuit

Under normal working conditions, the AC peak value between conductors or between any conductor does not exceed 42.4V or the DC value does not exceed 60V in the secondary circuit.

SELV circuit: safety extra low voltage circuit.

The secondary circuit is properly designed and protected so that under normal conditions or single fault conditions, between any two accessible parts, as well as any accessible parts and the protective earth terminal of the equipment (only for The voltage between Class I equipment) shall not exceed the safe value.

The above is the introduction of PCB design distance and related safety requirements. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology.