1 Scope and object
1.1 Scope
1.1.1 Equipment included in scope
This part of GB 4793 specifies general safety requirements for electrical equipment intended for professional, industrial process, and educational use, any of which may incorporate computing devices, as defined in a) to d) below, when used under the environmental conditions of 1.4.
a) Electrical test and measurement equipment
This is equipment which by electrical means tests, measures, indicates or records one or more electrical or non-electrical quantities, also non-measuring equipment such as signal generators, measurement standards, power supplies, transducers, transmitters, etc.
Note: All indicating and recording electrical measuring instruments (except those excluded in 1.1.2) fall within the scope of GB 4793 unless they are panel meters designed only for building-in to other equipment. Built-in panel meters are considered to be components and only need to meet the relevant requirements of GB 4793, or other standards, as part of the equipment into which they are built.
b) Electrical control equipment
This is equipment which controls one or more output quantities to specific values, with each value determined by manual setting, by local or remote programming, or by one or more input variables.
c) Electrical laboratory equipment
This is equipment which measures, indicates, monitors or analyses substances, or is used to prepare materials, and includes in vitro diagnostic (IVD) equipment.
This equipment may also be used in areas other than laboratories, for example self-test IVD equipment may be used in the home.
d) Accessories intended for use with the above (for example, sample handling equipment).
1.1.2 Equipment excluded from scope
This standard does not apply to equipment within the scope of
a) GB 8898 (Safety requirements for audio, video and similar electronic apparatus);
b) GB 4706 (Safety of household and similar electrical appliances);
c) GB 4943 (Safety of information technology equipment, except as specified in 1.1.3);
d) GB 9706 (Medical electrical equipment);
e) GB/T 15283 (Class 0.5, 1 and 2 alternating current watthour meters);
f) GB 19212 (Power transformers, power supply units and similar);
g) IEC 60204 (Controls for electrical machines);
h) IEC 60364 (Electrical installations of buildings);
i) IEC 60439-1 (Low-voltage switchgear and controlgear assemblies).
1.1.3 Computing equipment
This standard applies only to computers, processors, etc. which form part of equipment within the scope of this standard or are designed for use exclusively with the equipment.
Note: Computing devices and similar equipment within the scope of GB 4943 and conforming to its requirements are considered to be suitable for use with equipment within the scope of this standard. However, some of the requirements of GB 4943 for resistance to moisture and liquids are less stringent than those in this standard. If hazards from moisture or liquids could affect equipment that conforms to GB 4943 and is used with equipment which conforms to this standard, the instructions for use should specify any additional precautions required.
1.2 Object
1.2.1 Aspects included in scope
The purpose of the requirements of this part is to ensure that the design and methods of construction used provide adequate protection for the operator and the surrounding area against
a) electric shock or burn (see clause 6);
b) mechanical hazards (see clauses 7 and 8);
c) excessive temperature (see clauses 9 and 10);
d) spread of fire from the equipment (see clause 9);
e) effects of fluids and fluid pressure (see clause 11);
f) effects of radiation, including lasers sources, and sonic and ultrasonic pressure (see clause 12);
g) liberated gases, explosion and implosion (see clause 13).
Note: Attention is drawn to the existence of additional requirements which may be specified by national authorities responsible for the health and safety of labour forces.
Foreword i
Introduction iii
1 Scope and object
1.1 Scope
1.1.1 Equipment included in scope
1.1.2 Equipment excluded from scope
1.1.3 Computing equipment
1.2 Object
1.2.1 Aspects included in scope
1.2.2 Aspects excluded from scope
1.3 Verification
1.4 Environmental conditions
1.4.1 Normal environmental conditions
1.4.2 Extended environmental conditions
2 Normative references
3 Terms and definitions
3.1 Equipment and states of equipment
3.2 Parts and accessories
3.3 Electrical quantities
3.4 Tests
3.5 Safety terms
3.6 Insulation
4 Tests
4.1 General
4.2 Sequence of tests
4.3 Reference test conditions
4.3.1 Environmental conditions
4.3.2 State of equipment
4.4 Testing in single fault condition
4.4.1 General
4.4.2 Application of fault conditions
4.4.3 Duration of tests
4.4.4 Conformity after application of fault conditions
5 Marking and documentation
5.1 Marking
5.1.1 General
5.1.2 Identification
5.1.3 Mains supply
5.1.4 Fuses
5.1.5 Terminals, connections and operating devices
5.1.6 Switches and circuit-breakers
5.1.7 Equipment protected by double insulation or reinforced insulation
5.1.8 Field-wiring terminal boxes
5.2 Warning markings
5.3 Durability of markings
5.4 Documentation
5.4.1 General
5.4.2 Equipment ratings
5.4.3 Equipment installation
5.4.4 Equipment operation
5.4.5 Equipment maintenance
6 Protection against electric shock
6.1 General
6.1.1 Requirements
6.1.2 Exceptions
6.2 Determination of accessible parts
6.2.1 Examination
6.2.2 Openings above parts that are hazardous live
6.2.3 Openings for pre-set controls
6.3 Permissible limits for accessible parts
6.3.1 Values in normal condition
6.3.2 Values in single fault condition
6.4 Protection in normal condition
6.5 Protection in single fault condition
6.5.1 Protective bonding
6.5.2 Double insulation and reinforced insulation
6.5.3 protective impedance
6.5.4 Automatic disconnection of the supply
6.6 Connections to external circuits
6.6.1 General
6.6.2 Terminals for external circuits
6.6.3 Circuits with terminals which are hazardous live
6.6.4 Accessible terminals for stranded conductors
6.7 Clearances and creepage distances
6.7.1 General requirements
6.7.2 Mains circuits
6.7.3 Circuits other than mains circuits
6.7.4 Measuring circuits
6.8 Procedure for dielectric strength tests
6.8.1 Reference test earth
6.8.2 Humidity preconditioning
6.8.3 Conduct of tests
6.8.4 Voltage tests
6.9 Constructional requirements for protection against electric shock
6.9.1 General
6.9.2 Enclosures of equipment with double insulation or reinforced insulation
6.9.3 Over-range indication
6.10 Connection to mains supply source and connections between parts of equipment
6.10.1 Mains supply cords
6.10.2 Fitting of non-detachable mains supply cords
6.10.3 Plugs and connectors
6.11 Disconnection from supply source
6.11.1 General
6.11.2 Requirements according to type of equipment
6.11.3 Disconnecting devices
7 Protection against mechanical hazards
7.1 General
7.2 Moving parts
7.3 Stability
7.4 Provisions for lifting and carrying
7.5 Wall mounting
7.6 Expelled parts
8 Mechanical resistance to shock and impact
8.1 Enclosure rigidity test
8.1.1 Static test
8.1.2 Dynamic test
8.2 Drop test
8.2.1 Equipment other than hand-held equipment and direct plug-in equipment
8.2.2 Hand-held equipment and direct plug-in equipment
9 Protection against the spread of fire
9.1 Eliminating or reducing the sources of ignition within the equipment
9.2 Containment of fire within the equipment, should it occur
9.2.1 Constructional requirements
9.3 Limited-energy circuit
9.4 Requirements for equipment containing or using flammable liquids
9.5 Overcurrent protection
9.5.1 Permanently connected equipment
9.5.2 Other equipment
10 Equipment temperature limits and resistance to heat
10.1 Surface temperature limits for protection against burns
10.2 Temperatures of windings
10.3 Other temperature measurements
10.4 Conduct of temperature tests
10.4.1 Temperature measurement of heating equipment
10.4.2 Equipment intended for installation in a cabinet or a wall
10.5 Resistance to heat
10.5.1 Integrity of clearances and creepage distances
10.5.2 Non-metallic enclosure
10.5.3 Insulating material
11 Protection against hazards from fluids
11.1 General
11.2 Cleaning
11.3 Spillage
11.4 Overflow
11.5 Battery electrolyte
11.6 Specially protected equipment
11.7 Fluid pressure and leakage
11.7.1 Maximum pressure
11.7.2 Leakage and rupture at high pressure
11.7.3 Leakage from low-pressure parts
11.7.4 Overpressure safety device
12 Protection against radiation, including laser sources, and against sonic and ultrasonic pressure
12.1 General
12.2 Equipment producing ionizing radiation
12.2.1 Ionizing radiation
12.2.2 Accelerated electrons
12.3 Ultraviolet (UV) radiation
12.4 Microwave radiation
12.5 Sonic and ultrasonic pressure
12.5.1 Sound level
12.5.2 Ultrasonic pressure
12.6 Laser sources
13 Protection against liberated gases, explosion and implosion
13.1 Poisonous and injurious gases
13.2 Explosion and implosion
13.2.1 Components
13.2.2 Batteries and battery charging
13.2.3 Implosion of cathode ray tubes
13.2.4 Equipment rated for high pressures
14 Components
14.1 General
14.2 Motors
14.2.1 Motor temperatures
14.2.2 Series excitation motors
14.3 Overtemperature protection devices
14.4 Fuse holders
14.5 Mains voltage selecting devices
14.6 High integrity components
14.7 Mains transformers tested outside equipment
14.8 Printed circuit boards
14.9 Circuits or components used as transient overvoltage limiting devices
15 Protection by interlocks
15.1 General
15.2 Prevention of reactivating
15.3 Reliability
16 Test and measurement equipment
16.1 Current measuring circuits
16.2 Multifunction meters and similar equipment
Annex A (Normative) Measuring circuits for accessible current (see 6.3)
Annex B (Normative) Standard test finger (see 6.2)
Annex C (Normative) Measurement of clearances and creepage distances
Annex D (Normative) Parts between which insulation requirements are specified (see 6.4 and 6.5.2)
Annex E (Normative) Reduction of pollution degrees
Annex F (Normative) Routine tests
Annex G (Informative) Leakage and rupture from fluids under pressure
Bibliography
Figure 1 Maximum duration of short-term temporary accessible voltages in single fault condition [see 6.3.2 a)]…………………………………………………………………..
Figure 2 Charged capacitance level in normal condition and single fault condition [see 6.3.1 c) and 6.3.2 c)] 37_Toc26945_Toc
Figure 3 Detachable mains supply cords and connections
Figure 4 Impact test using sphere
Figure 5 Flow chart to explain the requirements for protection against the spread of fire
Figure 6 Baffle
Figure 7 Area of the bottom of an enclosure to be constructed as specified in 9.2.1 b) 1)
Figure 8 Ball-pressure test apparatus
Figure 9 Ratio between hydraulic test pressure and rated maximum working pressure
Figure 10 Flow chart for conformity options 14.1 a), b), c) and d)
Figure A.1 Measuring circuit for a.c. with frequencies up to 1MHz and for d.c.
Figure A.2 Measuring circuits for a.c. with sinusoidal frequencies up to 100Hz and for d.c.
Figure A.3 Current measuring circuit for electrical burns
Figure A.4 Current measuring circuit for wet contact
Figure B.1 Rigid test finger (test probe 11 of GB/T 16842)
Figure B.2 Jointed test finger (test probe B of GB/T 16842)
Figure C.1 Examples of methods of measuring clearance and creepage distance
Figures D.1 a) to D.1 d) Protection between hazardous live circuits and circuits not exceeding the values of 6.3.2 in normal condition and having external terminals of accessible parts
Figures D.1 e) to D.1 h) Protection between hazardous live circuits and other circuits which do not exceed the values of 6.3.2 in normal condition and which have external terminals
Figure D.2 a) and D.2 b) Protection from a hazardous live internal circuit for an accessible part which is not bonded to other accessible) parts
Figure D.2 c) and D.2 d) Protection from a hazardous live primary circuit for accessible terminals of a secondary circuit which does not exceed the values of 6.3.2 in normal condition
Figure D.3 Protection of external accessible terminals of two hazardous live circuits
Figure G.1 Conformity verification process (see G.2)
Table 1 Symbols
Table 2 Tightening torque for screw assemblies
Table 3 Multiplication factors for clearance for altitudes up to 5 000m
Table 4 Clearances and creepage distances for mains circuits
Table 5 Clearances for circuits derived from mains circuits
Table 6 Clearance values for the calculation of 6.7.
Table 7 Creepage distances
Table 8 Clearances for measurement categories II, III and IV
Table 9 Test voltages for basic insulation
Table 10 Correction factors for test voltage according to test site altitude
Table 11 Physical tests on power supply cords
Table 12 Acceptable perforation of the bottom of an enclosure
Table 13 Limits of maximum available current
Table 14 Overcurrent protective device
Table 15 Surface temperature limits in normal condition
Table 16 Insulation material of windings
Table 17 Impulse withstand voltages
Table 18 Output impedance for impulse generators
Table C.1 Pollution degree table
Table E.1 Reduction of the pollution degree of internal environment through the use of additional protection
Table G.1 Test pressures for equipment with pressures above 14MPa
