GB 4793-2024 Safety technical specification for electrical equipment for measurement, control and laboratory use
1 Scope
This document specifies safety requirements for the following items of electrical equipment for measurement, control and laboratory use: marking and documentation, electric shock prevention, mechanical hazard prevention, resistance to mechanical stresses, flame spread prevention, temperature limit and heat resistance of equipment, protection against hazard from fluids and solid foreign objects, protection against radiation (including laser sources) and against sonic and ultrasonic pressure, protection against liberated gases and substances, explosion and implosion, components and subassemblies, protection by interlocks.
This document is applicable to the design, production, inspection and use of electrical equipment (including industrial automation equipment) for measurement, control and laboratory use.
2 Normative references
The following documents contain provisions which, through reference in this text, constitute provisions of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 4025 Basic and safety principles for man-machine interface, marking and identification - Coding principles for indicators and actuators
GB/T 4208 Degrees of protection provided by enclosure (IP code)
GB/T 5169.16 Fire hazard testing for electric and electronic products - Part 16: Test flames - 50W horizontal and vertical flame test methods
GB/T 7247.1 Safety of laser products - Part 1: Equipment classification and requirements
GB/T 19661 (All parts) Safety requirements for nuclear instrumentations and systems
GB/T 20138 Degrees of protection provided by enclosures for electrical equipment against external mechanical impacts (IK code)
GB/T 42125.1-2024 Safety requirements for electrical equipment for measurement, control and laboratory use - Part 1: General requirements
IEC 60027 (All parts) Letter symbols to be used in electrical technology
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 42125.1-2024 apply.
4 Environmental conditions
4.1 Normal environmental conditions
This standard applies to equipment designed to be safe at least under the following conditions:
a) indoor use;
b) altitude up to 2 000m;
c) temperature: 5℃~40℃;
d) maximum relative humidity 80% for temperatures up to 31℃ decreasing linearly to 50% relative humidity at 40℃;
e) mains supply voltage fluctuations up to ±10% of the nominal voltage;
f) transient overvoltages up to the levels of overvoltage category ll;
g) temporary overvoltages occurring on the mains supply;
h) applicable pollution degree of the intended environment (pollution degree 2 in most cases).
4.2 Extended environmental conditions
This standard applies to equipment designed to be safe not only in the environmental conditions specified in 4.1, but also in any of the following conditions rated by the manufacturer of the equipment:
a) outdoor use;
b) altitude above 2 000m;
c) ambient temperature: below 5℃ or above 40℃;
d) relative humidity above the levels specified in 4.1;
e) mains supply voltage fluctuations exceeding ±10% of the nominal voltage;
f) wet location;
g) transient overvoltages up to the levels of overvoltage category III or IV (see Annex A).
5 Marking and documentation
5.1 Marking
5.1.1 General
The equipment shall be provided with markings meeting the requirements of 5.1.2~5.2. Except for marking of internal parts, these markings shall be visible from the exterior, or be visible after removing a cover or opening a door without the aid of a tool, if the cover or door is intended to be removed or opened by an operator. Markings applicable to the whole equipment shall not be put on parts which can be removed by an operator without the use of a tool.
For rack- or panel-mounted equipment, markings are permitted to be on a surface that becomes visible after removal of the equipment from the rack or panel.
Letter symbols for quantities and units shall be as specified in IEC 60027 (All parts). If applicable, the graphic symbols shall meet the requirements of Table 1. Graphic symbols shall be interpreted in the document.
Note: The documents shall include installation manual, operation manual, maintenance instructions, etc.
5.1.2 Identification
The equipment shall, as a minimum, be marked with:
a) name or trademark of the manufacturer or supplier;
b) model, name or other method to identify the equipment. If equipment bearing the same distinctive designation (model) is manufactured at more than one locations, equipment from each manufacturing location shall be marked so that the location can be identified.
5.1.3 Power supply
The equipment shall be marked with the following information:
a) nature of power supply
1) a.c.: rated mains supply frequency or frequency range;
2) d.c.: the symbol is as shown in No. 1 of Table 1.
b) rated supply voltage or rated range of supply voltage;
c) The maximum rated power in W (active power) or VA (apparent power), or the maximum rated input current, with all accessories or plug-in modules connected. If the equipment can be used on more than one voltage ranges, separate values shall be marked for each voltage range unless the maximum and minimum values do not differ by more than 20% of the mean value. The marked value shall not be less than 90% of the maximum value.
d) equipment which an operator can set for different rated supply voltages shall be provided with means for the indication of the voltage for which the equipment is set. For portable equipment, the indication shall be visible from the exterior. If the equipment is so constructed that the supply voltage setting can be altered without the use of a tool, the action of changing the setting shall also change the indication.
e) accessory mains socket-outlets accepting standard mains plugs shall be marked with the voltage if it is different from the mains supply voltage. If the outlet is for use only with specific equipment, it shall be marked to identify the equipment for which it is intended. If not, the maximum rated current or power shall be marked, or symbol 13 of Table 1 placed beside the outlet with the full details included in the documentation.
5.1.4 Fuses
For any fuse which may be replaced by an operator, there shall be a marking beside the fuse holder, which will enable the operator to identify the correct replacement fuse.
5.1.5 Terminals, connectors and operating devices
5.1.5.1 General
If necessary for safety, an indication shall be given of the purpose of terminals, connectors, controls, and indicators, including any connections for fluids such as gas, water and drainage. Where there is insufficient space, symbol 13 of Table 1 may be used.
Push-buttons and actuators of emergency stop devices, and indicators used only to indicate a warning of danger or the need for urgent action, shall be colored red and coded as specified in GB/T 4025. If the meaning of color relates to the safety of persons or the environment, supplementary means of coding shall be provided (see GB/T 4025).
5.1.5.2 Terminals
Terminals for connection to the mains supply shall be identifiable. The following terminals shall be marked according to the following requirements:
a) symbol 5 of Table 1 is adopted for functional earth terminal;
b) symbol 6 of Table 1 is adopted for protective conductor terminals, except those as a portion of an approved mains appliance inlet. The symbol shall be placed on the terminal or close to it;
c) for the control circuit terminal that may be connected to accessible conductive parts, symbol 7 of Table 1 may be used if such connection of terminal is not obvious;
Foreword i
Introduction iii
1 Scope
2 Normative references
3 Terms and definitions
4 Environmental conditions
4.1 Normal environmental conditions
4.2 Extended environmental conditions
5 Marking and documentation
5.1 Marking
5.2 Warning markings
5.3 Durability of markings
5.4 Documentation
6 Protection against electric shock
6.1 General
6.2 Exceptions
6.3 Limit values for accessible parts
6.4 Primary means of protection
6.5 Additional means of protection in case of single fault condition
6.6 Insulation requirements
7 Protection against mechanical hazards
7.1 General
7.2 Sharp edges
7.3 Movable parts
7.4 Stability
7.5 Provisions for lifting and carrying
7.6 Wall mounting
7.7 Expelled parts
8 Resistance to mechanical stresses
9 Protection against the spread of fire
9.1 General
9.2 Eliminating or reducing the sources of ignition within the equipment
9.3 Containment of a fire within the equipment, should it occur
9.4 Limited-energy circuit
9.5 Requirements for equipment containing or using flammable liquids
9.6 Overcurrent protection
10 Equipment temperature limits and resistance to heat
10.1 Surface temperature limits for protection against burns
10.2 Temperatures of windings
10.3 Resistance to heat
11 Protection against hazards from fluids and solid foreign objects
11.1 General
11.2 Cleaning
11.3 Spillage
11.4 Overflow
11.5 Battery electrolyte
11.6 Equipment rated with a degree of ingress protection (IP code)
11.7 Fluid pressure and leakage
12 Protection against radiation, including laser sources, and against sonic and ultrasonic pressure
12.1 General
12.2 Equipment producing ionizing radiation
12.3 Optical radiation
12.4 Microwave radiation
12.5 Sonic and ultrasonic pressure
12.6 Laser sources
13 Protection against liberated gases and substances, explosion and implosion
13.1 Poisonous and injurious gases and substances
13.2 Explosion and implosion
14 Components and subassemblies
14.1 General
14.2 Motors
14.3 Overtemperature protection devices
14.4 Fuse holders
14.5 Mains voltage selection devices
14.6 Printed wiring boards
14.7 Circuit used to limit transient overvoltages
15 Protection by interlocks
15.1 General
15.2 Restart prevention
15.3 Reliability
16 Test methods
Annex A (Normative) Insulation requirements not covered by Subclause 6.6
A.1 Insulation for mains circuits
A.2 Insulation in secondary circuits
A.3 Insulation in circuits not addressed in 6.6, A.1 or A.2
Bibliography
Figure 1 Acceptable protection measures against electric shock
Figure 2 Capacitance level versus voltage in normal condition and single fault condition
Figure 3 Examples of binding screw assemblies
Figure 4 Distance between conductors on an interface between two layers
Figure 5 Distance between adjacent conductors along an interface of two inner layers
Figure 6 Distance between adjacent conductors located between the same two layers
Figure 7 Flow chart showing the requirements for protection against the spread of fire
Figure 8 Baffle
Figure 9 Area of the bottom of an enclosure to be constructed as specified in 9.3.2 c) 1)
Figure A.1 Distance between conductors on an interface between two layers
Figure A.2 Distance between adjacent conductors along an interface of an inner layer
Figure A.3 Distance between adjacent conductors located between the same two layers
Figure A.4 Example of recurring peak voltage
Table 1 Symbols
Table 2 Multiplication factors for clearances for equipment rated for operation at altitudes up to 5 000m
Table 3 Clearances and creepage distances for mains circuits of overvoltage category II up to 300V
Table 4 Test voltages for solid insulation in mains circuits of overvoltage category II up to 300V
Table 5 Clearances and test voltages for secondary circuits derived from mains circuits of overvoltage category II up to 300V
Table 6 Creepage distances for secondary circuits
Table 7 Minimum values for distance or thickness (see 6.6.3.4.2 to 6.6.3.4.4)
Table 8 Protective measures against mechanical hazards to body parts
Table 9 Minimum maintained gaps to prevent crushing for different body parts
Table 10 Maximum gaps to prevent access for different body parts
Figure 7 Flow chart showing the requirements for protection against the spread of fire
Table 11 Acceptable perforations of the bottom of an enclosure
Table 12 Limits of maximum available current
Table 13 Values for overcurrent protection devices
Table 14 Surface temperature limits in normal condition
Table 15 Maximum temperatures for insulation material of windings
Table 16 Test methods
Table A.1 Multiplication factors for clearances for equipment rated for operation at altitudes up to 5 000m
Table A.2 Clearances and creepage distances for mains circuits of overvoltage category II above 300V
Table A.3 Clearances and creepage distances for mains circuits of overvoltage category III
Table A.4 Clearances and creepage distances for mains circuits of overvoltage category IV
Table A.5 Minimum values for distance or thickness of solid insulation
Table A.6 Test voltages for solid insulation in mains circuits of overvoltage category II above 300V
Table A.7 Test voltages for solid insulation in mains circuits of overvoltage category III
Table A.8 Test voltages for solid insulation in mains circuits of overvoltage category IV
Table A.9 Clearances and test voltages for secondary circuits derived from mains circuits of overvoltage category II above 300V
Table A.10 Clearances and test voltages for secondary circuits derived from mains circuits of overvoltage category III
Table A.11 Clearances and test voltages for secondary circuits derived from mains circuits of overvoltage category IV
Table A.12 Creepage distances for secondary circuits
Table A.13 Minimum values for distance or thickness (see A.2.4.2 to A.2.4.4)
Table A.14 Clearance values for the calculation of A.3.2
Table A.15 Clearances for basic insulation in circuits having recurring peak voltages or working voltages with frequencies above 30kHz
Table A.16 Test voltages based on clearance
