Safe distance , including clearance ( spatial distance ) , creepage distance ( creepage distance ) and distance through insulation
Clearances : two adjacent conductor or a conductor with the shortest distance along the surface of the motor housing adjacent air measurements.
Creepage distance : The shortest distance between two adjacent conductors , or a conductor and an adjacent surface of the motor housing along the surface of the insulation must be measured.
Clearance decision:
According to the measurement of the operating voltage and insulation levels, you can determine the distance
A side line clearances size requirements
Electrical wiring of the secondary gap size
But usually : one side AC parts: fuse before L-N ≥ 2.5mm, LN PE ( earth ) ≥ 2.5mm, the fuse is not required after the device , but as much as possible to maintain a certain distance in order to avoid short-circuit damage to the power supply.
Primary part of ≥ 2.0mm AC -to-DC
Primary -side DC ground to the earth ≥ 2.5mm ( floating ground on the primary side of the earth )
A side portion of the secondary part of ≥ 4.0mm, between the components connected across a secondary
Electrical components of the secondary side of the gap clearance ≥ 0.5mm to
Secondary side to the earth ≥ 1.0mm to
Note : before deciding whether to comply with the requirements should be applied to the internal parts of the force 10N , 30N force to impose the shell to reduce their distance, so that is recognized as the worst case, the spatial distance still meet the requirements.
Creepage distance of the decision:
According to the working voltage and insulation levels , Table 6 may determine its creepage distance
But usually : ( 1 ) , a portion of the AC : Fuses before L-N ≥ 2.5mm, LN earth ≥ 2.5mm, after the fuse is not required , but keep a certain distance to avoid short-circuit damage the power supply.
( 2 ) , a portion of the AC -to-DC ≥ 2.0mm
( 3 ) , a surface- side DC ≥ 4.0mm such as one side of the earth ground
( 4 ) , the primary side to the secondary side of ≥ 6.4mm, such as optocouplers , Y capacitors and other parts ELEMENTS ≤ 6.4mm pin spacing to be slotted .
(5), ≥ 0.5mm between the part of the secondary side to
( 6 ) , to the secondary side than on the earth ≥ 2.0mm
( 7 ) , between the two levels of ≥ 8.0mm above the transformer
Distance through insulation :
Shall meet the following requirements under the operating voltage and insulation applications:
- For the working voltage does not exceed 50V (71V AC or DC peak value ) , no thickness requirements ;
- Additional insulation should be a minimum thickness of 0.4mm;
- When the reinforced insulation is not exposed in the normal temperature may result , the minimum thickness of the insulation should be strengthened to 0.4mm to any mechanical stress of the insulating material is deformed or when performance degradation .
If the insulation is provided with a protective housing in the device , and will not bump or scrape by maintenance personnel during operation , and in any case are as follows , the above-mentioned requirement does not apply regardless of how thin the thickness of the insulating material ;
- For additional insulation , use at least two layers of material , each layer of material through the additional insulation dielectric strength test ; Or:
- Additional insulation material composed of three layers , which can be any combination of two materials by additional insulation dielectric strength test ; Or:
- For reinforced insulation , use at least two layers of material , each layer of material through the strengthening of insulation dielectric strength test ; Or:
- Consists of three layers of insulating material reinforced insulation , which can be any combination of two materials, the dielectric strength test by reinforced insulation .
Note the point about the wiring process :
Flat -mount components such as capacitors , etc. , must be flat against , without dispensing
If two conductors impose 10N force can shorten the distance , is less than the safety distance requirements , you can dispense fixed this part to ensure that their clearances .
When laying PVC film, should be taken to ensure safety distance of some housing equipment ( note processing technology )
Parts Dispensing fixed careful not to make the PCB board has plastic wire and other foreign matter .
In the processing part , should not cause dielectric breakdown .
Material requirements regarding flame :
Shrink sleeve V-1 or VTM-2 above ; PVC sleeve V-1 or VTM-2 above
Teflon sleeve V-1 or VTM-2 above ; plastic material such as silica films, insulating tape V-1 or VTM-2 above
PCB board 94V-1 or more
There are about insulation class
( 1 ) , the working Insulation: Insulation equipment needed to work
( 2 ) Basic Insulation: provide basic protection against electric shock insulation
( 3 ) , additional insulation : Independent insulation applied in addition to the other basic insulation for protection in the event of failure of the basic insulation can still prevent electric shock
( 4 ) , double insulation : from the basic insulation and supplementary insulation consisting of
( 5 ) , reinforced insulation : A single insulation under the conditions specified in this standard , it provides a level of protection against electric shock equivalent to double insulation
Insulation suitable for all situations as follows :
A, operating insulation oprational insulation
a, ranging between two different voltage parts
b, ranging between ELV circuit ( or SELV circuit ) and a grounded conductive parts.
B, basic insulation basic insulation
a, between a dangerous voltage between conductive parts and grounded parts ;
b, between hazardous voltages and rely grounded SELV circuits ;
c, between the primary side of the power supply conductors and a ground shield between the core material or the main power transformer ;
d, as part of a double-insulated .
C, supplementary insulation supplementary insulation
a, in general , between the palpable between conductor parts and possible dangerous voltage parts with basic insulation after damage, such as :
Ⅰ, between the handles, knobs between the appearance of the handle or the like and ungrounded axis .
Ⅱ, between the metal shell and the second type of device power cord through this shell jacket .
Ⅲ, between ELV circuits and ungrounded metal case.
b, as part of a double-insulated
D, double insulation
Double insulation Reinforced insulation
Generally , between one side of the circuit and
between a, ungrounded accessible conductive parts, or
between b, floating (floating) of SELV circuits or
between c, TNV circuit
Double insulation = basic insulation + supplementary insulation
Note : ELV lines: extra-low voltage circuits
Under normal operating conditions , any communication between the conductor or conductors between the peak value of a does not exceed a value of not more than 42.4V DC 60V or secondary circuits.
SELV circuits: safety extra-low voltage circuits.
Made the proper design and secondary circuit protection , so that under normal conditions or under single fault conditions, the protective ground terminal between any two accessible parts, as well as any of the accessible parts and equipment ( only voltage class I devices) , will not exceed a safe value.
TNV: communications network voltage circuit
Under normal operating conditions, the communication signal carrying circuits . . . .
