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GB 9316-1988 Safety requirements for electronic flash devices for photography

Basic Information

Standard: GB 9316-1988

tandard name: Safety requirements for electronic flash devices for photography

Standard category:National Standard (GB)

state:Abolished

release date:1988-04-26

Implementation date:1988-12-01

Expiration date:2007-07-01

standard classification number

Standard ICS number:Imaging technology>>Photography technology>>37.040.10 Photography equipment, projectors

Standard Classification Number:Electrician>>Electrical lighting>>K73 special lamp

associated standards

alternative situation:Replaced by GB 9316-2007

Procurement status:eqv IEC 491-198

Publication information

publishing house:China Standard Press

other information

Review date:2004-10-14

Drafting unit:Electronic Standardization Institute

Focal point unit:National Photographic Equipment Standardization Technical Committee

Publishing department:Ministry of Electronic Industry of the People's Republic of China

competent authority:China Machinery Industry Federation

Introduction to standards:

Industry change standard GB 9316-1988 Safety requirements for electronic flash devices for photography GB9316-1988 Standard download and decompression password: www.bzxz.net

Some standard content:

National Standard of the People's Republic of China
Safety requirements for electronic flash apparatus for photographic purposes
Safety requirements for electronic flash apparatus for photographic purposes
GB9316-88
This standard is equivalent to international standards IEC491-1984 "Safety Requirements for Electronic Flash Devices for Photography". 1 Subject content and scope of application
1.1 This standard gives the safety requirements for electronic flash devices. 1.2 This standard applies to the following electronic flash devices for photography and their related devices that have an energy storage of not more than 2000J and are not affected by water droplets or splashes.
a.
A single flash device can have more than one flash head that can operate simultaneously; b. A flash device for continuous multiple exposure photography; c. A charger connected to an electronic flash device for photography and the power supply device, which may be part of the power plug; d. Accessory devices, such as light volume adjusters and flash synchronizers listed in the instructions. This standard does not apply to strobe devices.
Note: For flash devices with energy storage exceeding 2000, if there is no corresponding standard to be based on, this standard can be adopted within the applicable scope. In terms of power supply, the following types are applicable: a. Flash devices that operate with grid power; b. Flash devices that can be used with both grid power and batteries. Note: This standard applies to flash devices that can be used in both temperate and tropical zones. 1.3 This standard does not apply to devices whose rated power supply voltage to ground exceeds 250V (effective value). 1.4 This standard only covers the safety of flash devices and does not cover other performance (see Chapter 3). 2 Definition
2.1 Product type test: refers to a comprehensive series of tests on a certain number of samples that can represent this type of device. The purpose is to determine whether a manufacturer can produce products that meet this standard. 2.2 Manual: refers to operations that do not require the use of tools, coins or other objects. 2.3 Accessible parts: refers to parts that can be reached with a standard test finger (see Section 8.1.1). Note: It is assumed that the accessible surfaces of non-conductive parts are covered with a conductive layer (see clause 4.3.1). 2.4 Live parts: refers to parts with which contact may cause obvious electric shock (see paragraph 8.1.1). 2.5 Creepage distance: refers to the shortest distance measured along the surface of the insulating material between two conductive parts. 2.6 Gap: refers to the shortest distance between two conductive parts in the air. 2.7 Grid power supply: refers to a power supply with an operating voltage higher than 34V (peak value), and is not a power supply that only supplies power to the devices mentioned in Article 1.2. 2.8 Rated power supply voltage: refers to the power supply voltage specified by the manufacturer for the device. 2.9 Components directly connected to the grid power supply: refers to the components in the device that are electrically connected to the grid power supply. When the component is connected to a certain pole of the grid power supply, a current equal to or greater than 9A can be generated at the connection. The Ministry of Electronics Industry of the People's Republic of China approved the implementation on 1988-12-01 on April 26, 1988 | In the test to confirm that the component is directly connected to the grid power supply, the fuse in the device is not short-circuited. 2.10 Components conductively connected to the grid power supply: refers to the component in the device that is electrically connected to the grid power supply. When the device is not grounded, the component passes the 2000α The resistor is connected to one pole of the grid power supply, and a current greater than 0.7mA (peak value) is generated on the resistor. 2.11 Power supply equipment: refers to equipment that obtains energy from the grid power supply and supplies power to one or more devices. 2.12 Battery charger: refers to a device that is directly powered by the grid power supply and charges the battery when necessary. 2.13 Terminal piece: refers to a component of the flash device through which it is connected to external conductors or other devices. A terminal piece can have several contacts.
2.14 Thermal relay: refers to a device that can disconnect certain parts of the device from the power supply to prevent these parts from continuing to overheat. 2.15 Safety switch: refers to a mechanism that can cut off the power supply when the cover is opened. 2.16. Printed board: refers to a base material cut to the required size, with all mounting holes and at least one conductive circuit pattern. 2.17 Conductive circuit pattern: refers to the conductive pattern formed by the conductive material of the printed board. 2. Class 181 device: refers to a device whose anti-shock measures not only rely on basic insulation, but also include additional safety measures, that is, the accessible conductive parts in the device are connected to the protective (grounding) conductor of the fixed line. In the event of failure of the basic insulation, Accessible conductive parts are not live. Note: This type of device may have components belonging to the "Class" structure. 2. Class 191 devices: refers to devices whose protection against electric shock not only relies on basic insulation, but also includes additional safety measures, such as double insulation or reinforced insulation. Such devices It does not have protective grounding measures and does not rely on the installation conditions of the device. 2.20 Basic insulation: refers to the insulation that provides basic protection to live parts to prevent electric shock. 2.21 Supplementary insulation: refers to independent insulation added to the basic insulation. It can still prevent electric shock in the event of basic insulation failure. 2.22 Double insulation: refers to insulation including basic insulation and supplementary insulation. 2.23 Reinforced insulation: refers to a separate insulation system added to live parts, and its level of protection against electric shock is Equivalent to double insulation under the conditions specified in this standard
Note: The term "insulation system" does not mean that the insulation should be one layer, it can include several layers, and these layers cannot be used as supplementary insulation or basic insulation. Standalone withstand test.
General requirements
3
The design and structure of the device should ensure that no hazard occurs under normal use or fault conditions, in particular the following aspects: a. Prevent personal electric shock;
b. Prevent personal injury from high temperature;
c. Prevent fire
Generally, it should be under normal working conditions and fault conditions specified in 4.2 and 4.3. Carry out all specified tests to check whether the device is qualified.
4 General test conditions
4.1 Test guidelines
4.1.1 The tests conducted in accordance with this standard are type tests 4.1. 2 All tests should be carried out in the order of the provisions of this standard as far as possible and on the same device. 4.1.3 Unless otherwise specified, the test should be performed at an ambient temperature of 15 to 35°C, a relative humidity of 45% to 75%, and an air pressure. Performed under normal working conditions of 86~106kPa
4.1.4 Unless otherwise specified, then:
a. The waveform should be basically a sine wave;
b. Voltage and The current measurement should be carried out with an instrument that has no obvious effect on the measured value. 4.1.5 The test is based on the use of a fully charged battery or a newly activated dry cell. 4.2 Normal operating conditions
GB9316-88|| tt||Normal operating conditions are the conditions formed by the most unfavorable combination of the following conditions. 4.2.1 Any position in which the device is in normal use. 4.2.2 Use 0.9 times or more of any rated power supply voltage of the device. 1.1 times power supply. For devices with a certain rated power supply voltage range, there is no need to adjust the voltage adjustment device, but 0.9 times the lower limit of the rated power supply voltage range or 1.1 times the upper limit of the rated power supply voltage range. If necessary, use the device Power supply at 0.9 times or 1.1 times of a nominal value within the range of the power supply voltage marked on
Any rated frequency of the power supply voltage
For devices using batteries, use a fully charged or New battery powered devices of the specified type operate on all types of power sources specified for their design. 4.2.3 In addition to the power supply voltage adjustment device that shall comply with Article 13.6, the user-accessible control device for manual adjustment can be adjusted to any position. 4.2.4 Flash head, capacitor and other accessories are connected or not connected. 4.2.5 Devices that can work with either the grid power supply or its own power supply, connected to the grid power supply or not. 4.2.6 Any protective grounding terminal is grounded or not, and one pole of the isolated power supply used in the test is grounded. 4.3 Fault conditions
Working under fault conditions means applying each of the following conditions one by one in addition to the normal operating conditions described in Article 4.2, as well as other fault conditions related to them derived from logical reasoning. Generally, by analyzing and examining the device and its circuit diagram, the fault conditions that should be applied can be determined and applied in the most appropriate sequence. 4.3.1 If the creepage distance and clearance are less than the value shown in curve A in Figure 1, short-circuit them. If the insulator has a groove less than 1 mm wide, the creepage distance should not be measured along the surface of the groove, but only in its width direction. If the gap contains a series of two or more air gaps separated by conductors, any air gaps less than 1 mm wide will not be included in the calculation of the total distance, unless the total distance is less than 1 mm as required in Figure 1. However, individual air gaps smaller than 0.5mm are not counted.
Note: ①This does not mean 8.3.7 and 8.3.The dimensions of the insulation material specified in paragraph 8 are negligible. ② If the insulator is divided into two parts by a thin slit, the path along the slit should be taken into account when measuring the creepage distance and gap. ③The specified creepage distances and clearances are the minimum actual distances taking into account the tolerances of components and parts. ④ Paragraph 4.3.3 gives the method for measuring the creepage distance and gap of enameled wires. When a standard test finger is used to determine creepage distances and clearances between accessible parts and live parts, any accessible area of ??non-conductive parts is considered to be covered by a conductive layer (see Figure 2). The voltage values ??stated in Figure 1 were measured with the device connected to its rated supply voltage and reaching steady state. Creepage distances and clearances are measured with conductors and plugs in their normal positions. The peeling and peeling strength complies with GB4721 "General rules for copper-clad laminates for printed circuits", GB4722 "Test methods for copper-clad laminates for printed circuits", GB4723 "Copper-clad phenolic paper laminates for printed circuits" 》, GB4724 "Copper-clad epoxy paper laminates for printed circuits", GB4725 "Copper-clad epoxy glass cloth laminates for printed circuits" between two conductors on the printed board, if one of the conductors needs to If it is directly or conductively connected to one of the poles of the mains supply, the requirements for creepage distances and clearances are modified. The values ??in Figure 1 should be replaced by the calculated values ??of equation (1): 0
logd = 0. 78log 30 (the minimum distance is 0. 5 mm) where: d——creepage distance, mm;
U—peak voltage, V.
These distances can be determined with reference to Figure 8.
Such reduced creepage distances and clearances are only permitted in connection with overheating (see 10.2). Note: ① The above reduction value applies to the conductor itself, but does not apply to assemblies or welding terminals. (1)
tuw
GB9316-88
② When calculating the distance, the paint coating on the printed board is ignored. 10
8
for reinforced insulation
for basic insulation, supplementary insulation and fault condition testing 0.5
0.1.
20
40| |tt||80100
200
Figure 1
400
60080)1000
2000
A and use||tt| |4000
Voltage peak value, V
The component conductively connected to the 220~250V (effective value) grid power supply, the distance is equal to the corresponding value at the peak voltage of 354V. In the case of peak voltages above 4000V, use the voltage test method to determine whether creepage distances and gaps should be short-circuited (see 9.2). The voltage across the basic insulation is determined when the supplementary insulation is short-circuited. Conversely, the voltage across the supplementary insulation is measured when the basic insulation is short-circuited. The curve in Figure 1 is determined by the following values:
Curve A: 34V corresponds to 0.6mm;
354V corresponds to 3.0mm.
Curve B: 34V corresponds to 1.2mm;
354V corresponds to 6.0mm.
Under certain conditions, the distance can be reduced according to the provisions of Sections 4.3.3 and 8.3.5. 4.3.2 Short-circuit or open-circuit the semiconductor device and filament if possible. Short-circuit or open-circuit the nixie tube (used for indication or control). 4.3.3 Short-circuit the insulation layer composed of lacquer, enamel or fiber fabric. These coverings are ignored when calculating creepage distances and clearances as specified in Figure 1. However, if enamel is used as an insulation layer for conductors and can withstand the voltage test specified in Table 1, it can be considered to increase the creepage distance and clearance by 1 mm.
Note: This does not mean that the insulation between coil turns, insulation sleeves or insulation tubes must also be short-circuited. Nominal diameter
mm
0.020
0.025
0.032
0.040
0.050
0.063
0.071
0.080
0.090
0.100
Minimum breakdown voltage
(effective value)
V
130| |tt||160
200
260
300
450
500
500
600||tt ||600
GB9316-88
Table 1
Nominal diameter, mm
Large
in
0.10||tt| |0.125
0.160
0.200
0.250
0.315
0.400
0.500
0.710
0.830
0.950
is less than or equal to
0.125
0.160
0.200
0.250
0.315
0.400
0.500
0.710
0.850
0.950
1.120
When testing at room temperature indoors, at least one of the five tested samples There are 4 samples that do not breakdown 4.3.4 electrolytic capacitor short circuit at the corresponding voltage not greater than Table 1.
Minimum breakdown voltage
(effective value)
V
1700
2.000
2200
2500|| tt||2800
3100
3500
4000
4400
4 700
4900
4.3.5 occurs Insulating parts to prevent electric shock or overheating that may be damaged in the event of a short-circuit fault shall be short-circuited, except for insulating parts that meet the requirements of Article 9.2.
4.3.6 To prevent electric shock or overheating capacitors, resistors, and inductors (except transformers and motors) that may be damaged when a short circuit or open circuit fault occurs, the most unfavorable of the two situations, short circuit or open circuit, must be selected. This fault condition does not apply to:
resistors complying with the requirements of 10.2 and 13.1; a.
b.
c.
d.||tt| |Inductors that meet the requirements of Section 13.8.1;
Capacitors that meet the requirements of Article 13.2 with a terminal voltage not exceeding 354V (peak); capacitors with self-restoring properties related to overheating (such as metallized paper). Note: By inspecting the device and analyzing its circuit diagram, it can be determined which parts or components have short circuits or open circuits that could impair the requirements for protection against electric shock or overheating (see clauses 4.3.5 and 4.3.6).
Loosen the fastening screws or similar holding the live parts housing in place a quarter turn. 4.3.7
4.3.8 For battery chargers and power supply equipment, connect the most unfavorable load impedance to its output, including short circuits. 4.3.9 Connect the battery charger and power supply equipment to a 250V AC power supply voltage that is independent of the rated power supply voltage or the voltage of the battery charger and power supply equipment. If there is a voltage adjustment device, set it to the most unfavorable position. 4.3.10 The refrigeration device stops working.
If the device is equipped with the following motors, brake the moving parts of the device: 4.3.11
a.
b.
4.3.12||tt| |Motors with brake rotor torque less than full load torque; motors mated to moving parts that may become jammed due to mechanical failure or manual jamming (as long as such failure or manual jamming is possible). Motors, relay coils, etc. that work for short periods of time or intermittently must work continuously if there is a possibility of accidental failure of continuous operation.
5 Marking
5.1 General requirements
GB9316-88
Devices should be marked according to the requirements of Articles 5.2 and 5.3. The mark should be:
a. When preparing to use the device, it should be easy to see clearly and avoid misunderstanding; b. It cannot be erased and the writing must be clear.
Check compliance by visual inspection and the following tests. Wipe gently with a cloth soaked in gasoline or water and the mark should not be removed. Note: It is best to mark the mark on the surface of the device. If the location of the mark is specified in the instruction manual, it is allowed to place the mark in other locations that are easily accessible. Text symbols for quantities and units should comply with the requirements of corresponding national standards. Graphic symbols should comply with the requirements of GB5465.2 "Graphic Symbols for Electrical Equipment". The marking of fuses shall comply with the requirements of Section 13.3.2. The marking of the grid power switch shall comply with 13.4.3 requirements. Check compliance by visual inspection.
5.2 Nameplate
The device should be marked with:
a manufacturer’s name or registered trademark;
b. model or name.
Check whether it is qualified by visual inspection.
Note: ① The double box symbol " can be used to mark Class 1 devices. ② This symbol should be placed in an obvious position in the technical instructions and will not be easily confused with the manufacturer's name or registered trademark. 5.3 Power supply ||tt| |The device should be marked as follows: bzxz.net
a. The nature of the power supply:
AC is represented by the symbol "~";
DC is represented by the symbol "——" or "" (only suitable for battery device) indicates. b. The rated supply voltage or voltage range that can be used without adjusting the voltage adjustment device, unless the device is powered only by an isolated power supply device
c. For devices that can be adjusted to different rated supply voltages. , its structure should ensure that the adjusted voltage indication can be clearly seen when the device is ready for use. If the device is designed to allow the user to adjust the power supply voltage, it is required that when the voltage adjustment device is changed, the voltage indication will also change accordingly. || tt||Note: For the case where the battery charger and power supply device are integrated with the mains power plug, it is allowed to mark the voltage adjustment indicator of the device on the joint surface of the plug
d. If the safety is consistent with the mains power supply used. If the frequency is correct, mark the rated grid power frequency (or frequency range) in Hertz
Check whether it is qualified by visual inspection
5.4 Instructions for use||tt| |5.4.1 The battery charger and power supply device should have separate instructions indicating the type of flash device they are suitable for. The flash device should also have separate instructions indicating the type of power supply device or battery charger it uses. Note: This is also possible. Mark these contents on these objects. Check for compliance by visual inspection
5.4.2 The instructions for use shall indicate that the device shall not be exposed to water drops or splashes.
GB9316—88
5.4.3 The instruction manual should include warnings for the following situations: a. The battery cannot be exposed to overheating, such as sunlight or fire; b. Dry batteries cannot be charged. ||tt| |Check compliance by visual inspection
5.5 Termination device
The termination device shall be marked with the following symbols:
a. If there is a protective earth terminal: marked with the symbol "+ ". b. In addition to the terminals connected to the grid power supply and the grid power socket, the terminal pieces that are live under normal operating conditions: marked with the symbol "5" the lightning arrow should point to the terminal piece.
Note: This symbol It is only used to indicate the presence of live terminals. It shall not be used to mark non-live terminals to avoid stricter insulation requirements. Compliance shall be checked by visual inspection. The mark of the protective grounding terminal does not need to be visible from outside the machine (see 14.4). . Note: AC and DC devices can be marked with the symbol: "~". 6 Temperature rise under normal working conditions
6.1 During normal use, no part of the device shall reach an unsafe temperature. Put the device under the conditions specified below, and monitor its temperature immediately after these conditions are imposed to check whether it meets the requirements. If the device is powered by grid power, it should be turned on without flashing for 4 hours; if it is powered by dry batteries or accumulators only. , it should be paralleled for 30 seconds.
Then the device capable of producing continuous flashes is used to perform multiple consecutive flashes as fast as possible, but no more than 40 times. The number of flashes is determined by the instructions on the device. If there is no indication, it shall be determined based on 85% of the measured maximum peak voltage value of the flash capacitor. The device operates at its rated voltage.
Connect the battery charger to the completely discharged battery for 4 hours. The model of charger should match the battery. Determination of temperature:
For coils, use the resistance method:
For other cases, any other suitable method may be used. Note: When measuring coil resistance, the influence of the circuit and load connected to the coil can be ignored. The temperature rise should not exceed the value given in column 1 of Table 2. 6.2 In normal use, if the components that are conductively connected to the grid power supply carry a current exceeding 0.5A and generate a large amount of heat in the event of poor contact, the insulating materials supporting these components should be heat-resistant. In the case where there are two sets of conductors, each covered with insulating material, but can be rigidly connected or contacted (such as plugs and sockets), only the insulation of one set of conductors needs to be tested. If one set of insulators is fixed to the device , the insulator should be tested. The insulating material shall be subjected to the test described in Note ③a in Table 2 to check compliance with the requirements. The softening temperature of the insulating material should be at least 150°C. Note: Examples of components that can generate significant amounts of heat during normal use include switch contacts, voltage adapter contacts, screw terminals, and fuse boxes. External parts
Installation
Setting
Metal parts: knobs, handles, etc.
Case
Non-metal parts: knobs, handles, etc.||tt| |Casing
Inside of the insulating material casing
Winding
Unimpregnated silk, yarn and other insulated wires
Impregnated silk, yarn and other insulated wires| | tt | |tt||Without mechanical stress
With mechanical stress
Natural rubber insulation
Other insulating materials other than thermoplastics, unbroken paper
Not soaked Impregnated cardboard
part
impregnated yarn, silk, paper and textile fabrics, urea resin GB9316-88
Table 2
piece
phenol Formaldehyde resin bonded laminates, fiber filler phenol formaldehyde moldings
mineral filler phenol formaldehyde moldings
epoxy resin bonded laminates
natural rubber
Thermoplastic materials?
Allowable temperature rise value, K
Normal working conditions
1
30
40
50||tt| |60
55
70
70
85
Press the relevant winding
60
45||tt| |45
55
60
70
85
95
120
45
this The temperature rise value in the table is based on the maximum ambient temperature of 35°C and is measured under normal working conditions. Failure Condition
1
65
65
65
65
?
75
100
135
150
100
100
100
70
80
90|| tt | | 110 | | tt | | 130 | | tt | | 150 | The temperature rise reaches 65K. ②If the temperature rise value in this table exceeds the allowable temperature rise value of the corresponding insulation material grade, the allowable temperature rise value of the material shall prevail. ②The allowable temperature rise inside the insulating material machine shall be the temperature rise value of the corresponding casing material. ④The allowable temperature rise value in this table is formulated according to the corresponding material standards. The materials in the table are listed as examples only. For other materials not listed. The allowable temperature rise value cannot exceed the allowable temperature rise value proven after experiments. ③Natural rubber and synthetic rubber are not considered thermoplastic materials. ③Because there are many types of thermoplastic materials, it is impossible to determine the allowable temperature rise value. When it comes to this problem, the following method a can be used. On a separate sample of the material, measure the softening temperature under the conditions specified in GB1633 "Softening Point of Thermoplastic Plastics (Vicat) Test Method", and make the following corrections: | |tt||The penetration depth is 0.1mm;
Before zeroing the tester or recording the initial reading, add a total pressure of 10N (1kgf). b. The temperature limit used to determine the temperature rise is, GB9316-88
under normal use conditions, 10°C lower than the softening temperature value obtained in item a; - under fault conditions, equal to the softening temperature value. This table does not apply to materials used in resistors. 7. Anti-deformation in high-temperature environments
Under high temperatures, the casing of the device should have sufficient resistance to deformation. Check compliance with the following test.
At a temperature of 70±2C, make the load withstand GB2423.2 Test Bb specified in "Basic Environmental Testing Procedures for Electrical and Electronic Products Test B: High Temperature Test Method", the test temperature is 70±2℃, and the test is carried out for 2d (48h). After the test, the device shall be free from damage within the scope specified in this standard. 8 Electric shock hazard under normal operating conditions
8.1 External test
8.1.1 General requirements
Accessible parts and terminals connected to the camera synchronization device must not be live. In order to determine a certain component Whether it is accessible (see 2.3), the hinged test finger shown in Figure 3(a) or the rigid test finger shown in Figure 3(b) can be used to test at every possible position. When in doubt, apply a maximum force of 30N (3kgf). This test shall be performed on each external surface of the device.
Use the top of the test finger when applying force to avoid wedge or prying movements. Note: When using a rigid test finger with the applied force as described above, the test should be conducted around any openings or where deformation would cause cracking. At the same time, a spliced ??test finger is used to determine whether live parts have become accessible without applying force. During the test, the distance between accessible metal parts and live parts shall not become less than the value given in Figure 1, and live parts shall not become accessible.
Note: It is recommended to use an electrical contact indicating device with a voltage value of approximately 40V to indicate contact with conductive parts. In order to determine that a component or terminal contact is not live, the following measurements should be made first between any two components or contacts, and then between any component or terminal contact and a pole of the power supply. The measurement shall be carried out 2 seconds after the plug or connector is pulled out from the corresponding socket or connecting jack. If possible, a flash should be used during the measurement. Components or terminal contacts will be considered non-energized under the following conditions: the current flowing through each component or contact measured by a 50000Ω non-inductive resistor does not exceed 0.7mA (peak) AC or 2mA DC. And
a. For those with a peak voltage between 34 and 450V, the capacitance does not exceed 0.1μF; b. For those with a peak voltage between 450 and 15kV, the discharge capacity does not exceed 45μC. For frequencies above 1 kHz, multiply the limit value of 0.7 mA (bee value) by the frequency value in dry kilohertz, but should not exceed 70 mA (peak value).
Note: ①The above capacitance is the rated value.
② It can be seen from the above test requirements that if the voltage on the component exceeds AC 34V (peak) or DC 100V, the power supply impedance should be designed so that the current flowing through the 50000Ω resistor does not exceed AC 0.7mA (peak) or DC 2mA. 8.1.2 Operating shaft
The operating shaft should not be electrified.
Check compliance by measurement.
8.1.3 Ventilation holes
Ventilation holes or other holes above live parts should be designed so that external suspended objects (such as necklaces) entering the device cannot interact with any
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