Safe voltage is to prevent electric shock accidents by using specific power supply voltage series. Its power supply needs to be isolated from the input circuit and other electrical systems. Under normal and fault conditions, the upper limit value of the voltage series between any two conductors and the ground shall not exceed the effective value of 50 volts AC (50-500 Hz).
According to the characteristics of the site, the AC safe voltage grade specified in China safe voltage standard is adopted:
1, 42 volts (no-load upper limit is less than or equal to 50 volts) can be used for hand-held electric tools used in places with electric shock danger;
2, 36 volts (no-load upper limit is less than or equal to 43 volts), can be used in mines, conductive dust and other places;
3. For some live equipment that the human body may accidentally touch, you can choose 24 volts, 12 volts and 6 volts (the upper limit of no-load is less than or equal to 29 volts, 15 volts and 8 volts respectively). When working in large boilers, metal containers or generators, 12V or 6V low-voltage running lights must be used to ensure personal safety. When the electrical equipment adopts safe voltage of more than 24 volts, measures must be taken to prevent direct contact with charged bodies. Its circuit must be insulated from the earth. Safe voltage is determined according to the product of human allowable current and human resistance.