MindMap Gallery Electrical safety technology
This is a mind map about electrical safety technology. The main contents include electrical accidents and hazards, electric shock protection technology, electrical fire and explosion protection technology, lightning strike and electrostatic protection technology, and electrical safety device technology.
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Electrical safety technology
Electrical Accidents and Hazards
Classification
electric shock
Electric shock: electric current passing through the body (internal injury)
Direct electric shock (subjective)
Touching equipment that is normally live
Indirect electric shock (passive)
Touching equipment that is not powered under normal conditions
The equipment shell is called an exposed, non-electrically conductive external part.
According to the path of current flow
single line shock
Two-wire shock
step shock
Electrical injury: No exposure to electric current (trauma)
Electrical current burns: generally occur with low-voltage equipment
Arc burn: The most dangerous electrical injury that occurs in high-voltage equipment.
Electrocautery: permanent scarring
Skin metallization The metal melts and vaporizes and enters the skin to repair it
Mechanical damage: interrupted by electricity
photoophthalmia
electrical fire explosion
lightning strike
static electricity
Electromagnetic radiation: above 100Hz
The effect of electric current on the human body
Current size
Sensing current: 1mA
Get rid of current: 10mA
Ventricular fibrillation current: 50mA
Current influence
There is no completely safe way (the left hand to the chest is the most dangerous)
The longer the duration, the more likely ventricular fibrillation is
People are more sensitive to alternating current
Human body impedance: 2000-3000Ω (temperature is not an influencing factor)
Analysis of electric shock accidents
Electric shock protection technology
direct
insulation
Insulating material properties
Electrical properties: withstand voltage strength, dielectric constant (insulation polarization characteristics: the larger the dielectric constant, the slower the polarization)
Mechanical properties
Thermal properties: heat resistance (allowable operating temperature), arc resistance (resistance to carbonization when exposed to arc), flame retardant properties (oxygen index 21% 27%), softening temperature and viscosity)
Moisture absorption performance
Anti-biological properties
insulation breakdown
Gas will recover quickly after breakdown
Liquids can only recover to a certain extent after breakdown (the higher the density, the harder it is to breakdown)
Solids will lose their original properties after breakdown: electrical breakdown, thermal breakdown
Screen protection (separation)
Barrier: height 1.7m, 0.1m above the ground, 0.8m from the bare conductor, 0.2m spacing between bars
Fence: indoor height 1.2m, outdoor fence 1.5m
Metal parts need to be grounded and put up warning signs
indirect
Protection system: IT TT TN (the neutral point of the first letter is grounded, and the shell of the second letter is grounded; grounding is T
Ground protection
IT (protective grounding): 380V 4Ω; no more than 100kV 10Ω; control the leakage voltage within a safe range
TT: Generally, the leakage voltage cannot be controlled within a safe range; install a leakage protector; generally not used
Connect to zero to protect TN (S: open C: close)
TN-S: Safest: Hazardous Locations
TN-C-S: Substation, non-production plant
TN-C
Ground resistance: 4Ω; high soil resistance area 10Ω
Quick break time: fixed equipment 5S; mobile equipment 200V 0.4S 380V 0.2S
Equipotential bonding: total 6mm2 wire; 4Ω
protective conductor
Prioritize the use of natural conductors; for low-voltage systems, pipes that do not flow through flammable liquids and gases can be used; switches cannot be connected to the line; the equipment shell must not be used as a protective conductor
With protection 2.5 copper 10, without protection it is 4 aluminum 16
When the phase line is not greater than 16, it is equal to the phase line cross-section; when the phase line is between 16 and 35, it is equal to 16; when the phase line is greater than 35, it is equal to the phase line/2
G
Priority is given to using natural conductors for grounding wires in non-explosive environments; pipe protection for easily damaged parts of railways and highways; overlap welding of underground parts; adding jumpers to expansion joints; and taking relaxation measures when there is vibration
The upper end is 0.6m from the ground, below the freezing layer; 3m from the lightning rod to the ground; 1.5m from the wall
double insulation
Double insulated equipment is not Class II equipment; it is marked with the word "return"; it is not allowed to be grounded again.
structure
working insulation
2Ω
protective insulation
Can touch 5Ω
electrical isolation
Transformer: double insulation; the secondary side remains independent; it must not be connected to the earth; the shells of each equipment are connected at equal potential; the secondary side voltage cannot be too high 500v and the line must not be too long 200 meters
Both defense and defense
Extra low voltage (safety voltage)
Manual 42V; hand-operated 36V or 24V; limited 12V; water 6V; equipment powered by extra-low voltage is Class III equipment
Safe power supply and loop configuration
Single-phase power supply capacity 10KVA; electrical isolation; short circuit protection installed; secondary side shall not be grounded
Leakage Protection
Main protection against indirect electric contact
Place of use: Dr. Shi is out in the field alone
Electrical fire and explosion protection technology
electrical ignition source
Dangerous temperature: iron core overheating (coil voltage is too high and cannot pull in, resulting in increased eddy current loss and hysteresis loss); leakage; voltage is too high or too low
Sparks and arcs
Working sparks: sparks generated when a circuit is connected or disconnected
Accident sparks: generated under abnormal conditions; lightning, static electricity, electromagnetic induction
Equipment reasons
Hazardous materials and explosive environments
Hazardous material parameters
Flash point
Randian
Ignition temperature (auto-ignition point)
explosion limit
Minimum ignition current ratio: to methane
Maximum test safety gap
Minimum ignition energy (minimum ignition energy)
Explosive environment: Category 1 gas, Category 2 gases other than gas; Category 3 dust
Classification of explosive hazardous environments
Area 0 appears continuously; Area 1 may appear; Area 2 does not appear normally.
Release source classification: continuous release source, first-level release source (periodic release), second-level release source (normal no release); good ventilation can reduce the level, poor ventilation can increase the level, and pits can be improved
Explosive dust environment classification: 20 appears continuously, 21 appears periodically, 22 does not appear normally
Explosion-proof electrical equipment
Classification: Flameproof type d, increased safety type e, oil-filled type o, intrinsically safe type i, positive pressure type p
Equipment protection level EPL (one, two, three, buy one): The first type of environment uses the first type of equipment Ma Mb; the second type of environment uses the second type of equipment Ga Gb Gc; the third type of environment uses the third type of equipment Da Db Dc; a is the best
Explosion-proof electrical equipment identification: Ex dⅡB (Class II b environment) T3 Gb (protection level)
Line laying requirements
Area 22 can have connectors
1.5 times the rod distance from the explosive environment
The alarm device will alarm when it is set at 10% of the lower explosion limit.
PVC pipes cannot be used in explosive environments
Lightning strike and electrostatic protection technology
Lightning classification
Strike directly
Thousands of volts
induction mine
Hundreds of kilovolts
ball mine
harm
fire and explosion
electric shock
Damage to equipment and facilities (mechanical effects)
massive power outage
Lightning protection building
Category 1 lightning protection buildings: calcium carbide warehouses, acetylene manufacturing sites, areas 0, 20, and areas 1 and 21 with high explosion risk
The second type of lightning protection buildings: national, large and tank
Category III lightning protection buildings: provincial level
Lightning protection device classification
Internal: lightning protection equipotential, lightning protection spacing, lightning arrester and surge protector (installed at the incoming end; the normal state is open circuit, and lightning strikes become a path)
External: air-termination device (metal roof; spacing according to rolling ball radius 30 45 60), down conductor (replace if 30% rusted, grounding device (not more than 10Ω)
static electricity
Charging method: contact separation charging; breaking charging; induction charging; charge migration
Factors affecting static electricity: the tendency of impurities to enhance static electricity; process equipment and process parameters (contact area, contact pressure); humidity
Electrostatic characteristics: high voltage; slow leakage; various discharge point forms
Protective measures: Environmental hazard control; process control; grounding (eliminate static electricity on conductors); humidification; antistatic additives; static eliminators (eliminate static electricity on non-conductors)
Electrical safety device technology
Low voltage electrical equipment
Shell protection grade IP①②; ①Dust-proof 0-6 (none, 50, 12, 2.5, 1, dust-proof, dust-tight) ②Waterproof 0-8 (no dripping, splashing, spraying, submersible)
Low voltage equipment classification
Category 0: Basic insulation
Category 1 equipment: with metal casing and internal PE grounding
Class II equipment: basic insulation, protective insulation, grounding prohibited (double insulation)
Category III equipment: extra low voltage equipment, no grounding
Safety requirements: double-pole switch, double fuse
Lighting requirements: There is a lighting main switch at the entrance, 24V for extremely humid places, a bipolar switch in the distribution box, and a single-pole switch for lighting equipment on the live line; explosion-proof for explosive environments; waterproof for humid environments.
Low voltage electrical appliance classification
Control electrical appliances: circuit breaker (can break short-circuit current) contactor (cannot break short-circuit current, can be operated frequently)
Protective appliances: thermal relay (used for main circuit, with large delay, used for overload protection, cannot be used for short-circuit protection); fuse (action open, not used for overload protection)
High voltage electrical equipment
Distribution substation
High-voltage distribution room has a second-level fire resistance rating, low-voltage distribution station has a third-level fire resistance rating, and oil-immersed transformer room has a first-level fire resistance rating.
Door opens outward
10KV 60kg oil immersed is isolated with non-combustible partitions, 60-600kg is isolated with solid walls, and more than 600 independent rooms
High voltage switch
Circuit breaker: powerful arc extinguishing device; load switch: simple arc extinguishing device and fuse used in series; isolation switch: no arc extinguishing function
Electrical wiring
Electrical safety monitoring instruments
Insulation resistance measuring instrument (megohmmeter): Do not use double-stranded insulated wires; place points before and after measurement; measure just after power outage
Ground resistance measuring instrument: do not measure on rainy days;
Infrared Thermometer:
Combustible gas detector: alarm at the lower limit of 20%; the probe is close to valves and joints, and should not be larger than 1m