Circuit Breaker

Leakage current leakage circuit breaker in the circuit exceeds a predetermined value when the operation switch automatically. Leakage circuit breakers commonly divided into two types of voltage-and current-mode, and the current type is divided into two kinds of electromagnetic and electronic. Leakage circuit breaker is used to prevent physical shock, should be based on direct contact and indirect contact with two kinds of electric shock protection to select different requirements.
Type

Voltage-leakage circuit breaker for transformer neutral point grounded low-voltage grid. Characterized in that when the physical shock, the zero line to ground voltage appears a relatively high, causing the relay, the power switch trip.
Current-leakage circuit breaker is mainly used for transformer neutral point grounded low-voltage distribution systems. Which is characterized by personal electric shock when, by the zero-sequence current transformer detects a leakage current, the relay, the power switch is turned off.
Selection principles

Depending on the purpose and the place where the electrical equipment to choose
1) direct contact with the electric shock protection
Direct contact with an electric shock hazard due to relatively large, causing serious consequences, so to use high sensitivity leakage Circuit breaker for power tools, portable electrical equipment and temporary line, you should install the operating current in the loop is 30mA, operation time leakage circuit breaker within 0.1s. More on residential appliances, preferably into the household energy meter installed in the rear.
If once the shock easily cause secondary damage (eg aerial work), you should install the operating current in the loop is 15mA, operating time within the US leakage circuit breaker. For electrical medical equipment in hospitals, operating current should be installed as 6mA, operating time within the US leakage circuit breaker.
2) indirect contact electric shock protection
Different places indirect contact electric shock, can cause varying degrees of bodily harm, therefore, should be installed in different places different leakage circuit breaker. The dangers of electric shock for easy larger place, require relatively high sensitivity of leakage circuit breaker. In humid areas than in dry places much greater risk of electric shock, the general should be installed as the operating current 15-30mA, operation time within 0.1s leakage circuit breaker. For water, electrical equipment should be installed movements. Current of 6 - l0mA, operating time within the US leakage circuit breaker. The operator must stand on metal objects or metal container for electrical equipment, as long as the voltage is higher than 24V, you should install the operating current of 15mA or less operating time within the US leakage circuit breaker. Voltage of 220V or 380V for fixed electrical equipment, when the housing grounding resistance at 500fZ below, can be installed stand-alone operating current of 30mA, operating time within 0.19 leakage circuit breaker. 100A rated current at more large electrical equipment or electrical equipment with multiple power supply circuit, install operating current of 50 - 100mA earth leakage circuit breakers, grounding resistance for electrical equipment in 1000 or less, can be installed operating current of 200-500mA earth leakage circuit breakers.