Human body safety voltage
Industry regulations The safety voltage is not higher than 36V, the continuous contact safety voltage is 24V, and the safe current is 10mA. The degree of damage to the human body caused by electric shock depends mainly on the magnitude of the current through the human body and the length of the power-on time. The greater the current intensity, the greater the lethal risk; the longer the duration, the greater the likelihood of death. The minimum current value that can be felt is called the sense current. The AC is 1 mA and the DC is 5 mA. The maximum current that can be rid of after the person is shocked is called the current, the AC is 10 mA, the DC is 50 mA, and the DC is 50 mA. The life-threatening current is called the lethal current and the lethal current is 50mA. In the case of protection against electric shock, the current allowed by the human body is generally 30 mA.
What is the cause of electrocution?
1, electric shock
The death of a human or an animal is caused by the passage of electric current in the human body, which interferes with the bioelectricity of the nerve conduction of the human body, causing the brain to lose control of the body, or to feel abnormal stimulation, and to issue wrong commands to the muscles and organs. Especially when the current passes through the heart, the heart will squat and stop beating, which will lead to the death of the human body due to lack of oxygen. It is not that people with current will be electrocuted, depending on the magnitude of the current. The current is equal to the voltage divided by the resistance of the human body. Why is the battery not dead? Because the battery voltage is too low, the current generated in the human body is too small, people do not feel, and can not cause harm to people. The greater the current, the greater the likelihood that a person will be electrocuted. This means that the higher the voltage, the more dangerous.
2, electric burns
When the human body is exposed to a high voltage, a large current is generated in the body, which may cause burns, burns, etc. of the body due to the thermal effect of the current. It can be seen that no matter what kind of electric shock, the chief culprit in the death of humans and animals is the passage of electric current through the body. A necessary condition for generating current is that a closed loop must be formed.
Principle of safe voltage
According to Ohm's law (I=U/R), it can be known that the magnitude of the current flowing through the human body is related to the applied voltage and the body resistance.
In addition to human resistance, human body resistance should also be attached to clothing, shoes, pants and other electrical resistance outside the human body. Although the human body resistance can generally reach 5000Ω, there are many factors affecting the body's resistance, such as wet skin and sweat, with conductive The dust, the contact area and pressure of the charged body, and the damp oil of clothes, shoes and socks can all reduce the body resistance, so the current flowing through the human body cannot be calculated in advance.
Therefore, in order to determine the safety conditions, the safety current is often not used, but the safety voltage is used for estimation: under normal circumstances, that is, in an environment where the risk of being dry and the risk of electric shock is small, the safety voltage is regulated to 24V, and the electric shock is dangerous to the humidity. Larger environment (such as metal containers, welding and repairing in pipes), the safety voltage is regulated to 12V, so that the current through the human body during an electric shock can be limited to a small range, which can protect personal safety to a certain extent. .
When the body resistance is constant, the higher the voltage contacted by the human body, the greater the current passing through the human body, and the more serious the damage to the human body. But it is not that people will harm the human body when they touch the power supply. In daily life, we touch the poles of ordinary dry batteries with our hands, and the human body does not have any feeling. This is because the voltage of ordinary dry batteries is low (1.5 VDC). When the voltage applied to the human body is lower than a certain value, the voltage will not cause serious injury to the human body in a short time. We call this voltage a safe voltage.
What is the safety voltage and safe current of the human body?
36V in the case of dryness, 24V in a little bit, and only 12V in particularly humid conditions. 24V is dangerous under normal environmental conditions.
The safe voltage and current are synchronized. If the voltage reaches 1000V and the current is only 1mA, it will not harm the human body. For example, the current electronic mousetrap is commonly used, high voltage, low current. People encounter numbness, but there is no big danger.
Under normal circumstances, the current below 15mA, people can stay awake, you can get rid of. However, the current of 15 mA or more is dangerous to the human body. Depending on the environmental humidity, it may cause difficulty in getting rid of, and difficulty breathing.
The safety of electricity is relative, mainly depends on your contact and air and environmental conductivity.
How does the human body safety voltage 36V come from?
The body's resistance value mainly depends on the body's fatness and thinness, and is basically independent of external factors. Its value is about 500Ω, but the skin resistance varies greatly depending on the conditions, making the body resistance also in a large range. Change within.
There are many factors that affect the body's electrical resistance. In addition to the thick skin, the skin is damp, sweaty, damaged, and conductive dust will reduce the body's resistance. Increased contact area and increased contact pressure will also reduce body resistance. Increased contact voltage will break through the stratum corneum of the epidermis and increase the body's electrolysis, which will also reduce the body's resistance.
In addition, the body resistance is also reduced with the increase of the power frequency, for example, the body resistance at 100 kHz is about half of that at 50 Hz. Under normal circumstances, the body's resistance can be considered in the range of 1000 ~ 1500Ω, the lowest can be measured in 800Ω. According to experiments and analysis, the power frequency limit current allowed by the human body is about 50mA, so it can be calculated according to Ohm's law, U=IR≈0.05&TImes;800=40(V), and the maximum power frequency allowed by the human body is known. The voltage is approximately 40V.
Therefore, China's safety voltage is regulated at 36V and 12V. For those places with poor working conditions, such as large pipes, mines, boilers and other metal containers with good electrical conductivity, lower body resistance or increased contact opportunities, the safety voltage should be set lower, usually Take 24V or 12V. For 12V, it is also called absolute safety voltage.
China's safety voltage rating
The national standard "Safety Voltage" stipulates that the rating of China's safety voltage rating is 42V, 36V, 24V, 12V and 6V, which should be selected according to the working site, operator conditions, usage mode, power supply mode, line condition and other factors. The safe voltage is the voltage that does not cause a physical shock, generally less than 36 volts.
A safe voltage is a voltage that does not cause direct death or disability. The "safety extra low voltage" that allows continuous contact under normal environmental conditions is 24V. (may also be 36V, 12V AC/DC, 24V is the most common)
The national standard "Safety Voltage" (GB3805-83) stipulates that the rating of China's safety voltage rating is 42V, 36V, 24V, 12V and 6V, which should be selected according to the working site, operator conditions, usage mode, power supply mode, line condition and other factors. .
24V in buildings with high risk of electric shock.
It is 12V in buildings with special electric shock hazard.