Selected according to the purpose of use and the place where the electrical equipment is located
1) direct contact with the protection of electrocution
Because the direct contact with electrocution of the hazard is relatively large, caused by the consequences of the seriousness of the leakage circuit breaker should be selected with a higher sensitivity, the power tools, mobile electrical equipment and temporary lines, should be installed in the circuit with an action current of 30mA, the time of action in the 0.1s leakage circuit breaker. For residential houses with more household appliances, it is best to install them behind the incoming energy meter.
If once electrocution is easy to cause secondary injuries (such as working at height), should be installed in the circuit with an action current of 15mA, action time within the US leakage circuit breaker. For electrical medical equipment in hospitals, earth leakage circuit breakers with an action current of 6mA and an action time within US should be installed.
2) Indirect contact electrocution protection
Different places of indirect contact electrocution, can cause different degrees of personal injury, so different places should be installed in different leakage circuit breakers. For easy electrocution hazardous places, the requirement of a higher sensitivity leakage circuit breaker. In the wet place than in the dry place of electrocution risk is much greater, generally should be installed action current of 15-30mA, action time within 0.1s of the leakage circuit breaker. For electrical equipment in the water, should be installed. Current 6-l0mA, action time within the US leakage circuit breaker. For the operator must stand on metal objects or metal containers in the electrical equipment, as long as the voltage is higher than 24V, should be installed with an action current of 15mA or less, the action time within the US leakage circuit breaker. For fixed electrical equipment with voltage of 220V or 380V, when the shell grounding resistance is below 500fZ, the single unit can be installed with an action current of 30mA and an action time of 0.19 within the earth leakage circuit breaker. For the rated current of 100A or more large electrical equipment or power supply circuit with multiple electrical equipment, can be installed with an action current of 50-100mA earth leakage circuit breaker, the grounding resistance of the electrical equipment in the following 1000, can be installed with an action current of 200-500mA earth leakage circuit breaker.
Selected according to the normal leakage current of the circuit and equipment
1) single machine with leakage circuit breaker. Action current should be greater than 4 times the leakage current of the normal operation of the equipment.
2) leakage circuit breaker for branch lines, the action current should be greater than the normal operation of the line leakage current of 2.5 times, but also greater than the line leakage current in the largest leakage current of electrical equipment leakage current of 4 times.
3)Leakage circuit breakers for the main line or the total protection of the whole network, the action current should be greater than 2.5 times the leakage current of the normal operation of the grid.
If it is not easy to measure the leakage current of the line or electrical equipment, it can be estimated according to the following empirical formula:
Lighting circuits or residential electricity circuits: leakage circuit-breaker action current IDZ>ISJ/2000;
Mixed power and lighting circuits: leakage circuit-breaker action current IDZ>ISJ/1000. 1000.
The formula IDZ is the earth leakage circuit breaker action current, ISJ is the maximum current in the circuit.
1) single-phase 220V power supply electrical equipment should be selected two-pole two-wire type or single-pole two-wire type earth leakage circuit breaker.
2)Three-phase three-wire 380V power supply of electrical equipment, should be used three-pole four-wire or four-pole four-wire earth leakage circuit breaker.