The so-called safe voltage refers to the voltage series used by a specific power supply to prevent electric shock accidents. The upper limit of this voltage series, that is, the voltage between two conductors or between any conductor and ground, does not exceed the AC effective value of 50 volts under any circumstances. The ratings of safe voltage in China are 42, 36, 24, 12 and 6 volts. When the voltage used by electrical equipment exceeds safe voltage, measures must be taken to prevent direct contact with charged bodies according to regulations.
According to the characteristics of production and workplace, adopting safe voltage with corresponding grade is the fundamental measure to prevent electric shock casualties. According to the national standard "safe voltage" (GB 3805-83), the rated grades of safe voltage in China are 42V, 36V, 24V, 12V, 6V, which should be selected according to factors such as workplace, operator conditions, mode of use, power supply mode and line conditions.
Safe voltage (GB 3805-83) is the most authoritative basic standard about voltage that is not dangerous to people. After fully analyzing the data in the table, we can know that under the most unfavorable conditions (except medical treatment and human body immersion in water), this limit value is: 15 ~ 100 Hz AC voltage (effective value) does not exceed16V; ; The ripple-free DC is 35v, of which the value of 50Hz alternating current is 16V, which is far lower than the 36V that is still used in our engineering habits (even junior high school physics textbooks). Even lower than the safe ultra-low voltage specified in GB 4706. 1-98 (general requirements for the safety of household and similar electrical appliances) published by 1998.
I don't know what new regulations are in the Limits of Extra Low Voltage (ELV) GB/T 3805-2008, which came into effect on September 1 2008, but I can't find the full text yet.
The safe voltage value varies from country to country. According to the specific environmental conditions in China, the safe voltage value is defined as:
In buildings without high risk of electric shock, it is 65V.
24V in buildings with high risk of electric shock.
Buildings with special risk of electric shock are 12V.