The circuit breaker: can switch on, carry and break the current under normal circuit conditions, can also be switched on under specified non-normal circuit conditions, carry a certain time and break the current of a mechanical switch.
Micro Circuit Breaker, referred to as MCB (Micro Circuit Breaker), is the most widely used terminal protection electrical appliances in building electrical terminal distribution devices. It is used for single-phase and three-phase short circuit, overload and overvoltage protection below 125A, including four kinds of single-pole 1P, two-pole 2P, three-pole 3P and four-pole 4P.
The micro circuit breaker consists of an operating mechanism, a contact, a protection device (various release devices), an arc extinguishing system, etc. The main contact is manually operated or electrically closed. After the main contact is closed, the free trip mechanism locks the main contact in the closing position. The coil of the overcurrent release and the thermal element of the thermal release are connected to the main circuit in series, and the coil of the undervoltage release is connected to the power supply in parallel. When the circuit occurs short circuit or serious overload, the armature of the overcurrent trip device draws, making the free trip mechanism operate, and the main contact disconnects the main circuit. When the circuit is overloaded, the heat element of the thermal trip device heats up to bend the bimetal sheet and push the free trip mechanism to act. When the circuit is under voltage, the armature of the undervoltage releaser is released. Also allows the free trip mechanism to operate.
The residual current circuit-breaker: A switch that automatically operates when the residual current in the circuit exceeds a preset value. Commonly used leakage circuit breakers are divided into two categories: voltage type and current type, and current type is divided into electromagnetic type and electronic type. Leakage circuit breakers are used to prevent personal shock, and should be selected according to the different requirements of direct contact and indirect contact protection.
Choose according to the purpose of use and the place where the electrical equipment is located
1) Protection from direct contact with electric shock
Because the harm of direct contact electric shock is relatively large, the consequences are serious, so to choose a leakage circuit breaker with high sensitivity, for power tools, mobile electrical equipment and temporary lines, should be installed in the loop operating current of 30mA, operating time within 0.1s leakage circuit breaker. For residential homes with more household appliances, it is best to install it after entering the household energy meter.
If once electric shock is easy to cause secondary damage (such as working at altitude), a leakage circuit breaker with an operating current of 15mA and an operating time within US should be installed in the loop. For electrical medical equipment in hospitals, leakage circuit breakers with operating current of 6mA and operating time within US should be installed.
2) Indirect contact protection
Indirect contact electric shock in different places can cause different degrees of harm to the person, so different leakage circuit breakers should be installed in different places. It is required to use leakage circuit breakers with relatively high sensitivity for places where electric shock is more harmful. In wet places than in dry places the risk of electric shock is much greater, generally should be installed operating current of 15-30mA, operating time within 0.1s leakage circuit breaker. For electrical equipment in water, action should be installed. Leakage circuit breaker with current of 6-l0mA and operating time within US. For electrical equipment where the operator must stand on a metal object or in a metal container, as long as the voltage is higher than 24V, a leakage circuit breaker with an operating current below 15mA and an operating time within US should be installed. For fixed electrical equipment with a voltage of 220V or 380V, when the ground resistance of the housing is below 500fZ, a single machine can install a leakage circuit breaker with an operating current of 30mA and an operating time of 0.19. For large electrical equipment with a rated current of more than 100A or a power supply circuit with multiple electrical equipment, a leakage circuit breaker with an operating current of 50-100mA can be installed. When the grounding resistance of the electrical equipment is below 1000, a leakage circuit breaker with an operating current of 200-500mA can be installed.
Post time: Sep-19-2023