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Both air circuit breaker (ACB) and molded case circuit breaker (MCCB) are used for the safe switching on and off of electrical systems. In principle, both serve the same purpose. The ACB is usually found on the upstream side of the circuit, while the MCCB is found on the load-side control (usually, the load-side switch operates more frequently than the upstream). These three protection devices are selected according to the required operating voltage and protection level (fault level) of the system. As technology continues to advance, the ratings and breaking capacities of MCCBs are increasing, so the applications of ACBs and MCCBs may overlap.
What is a molded case circuit breaker？
MCCBs are also known as device circuit breakers. All parts are sealed in plastic casings. Auxiliary contacts, undervoltage releases and shunt releases are mostly modular. Due to its very compact structure, molded case circuit breakers are basically impossible to repair. Most of them use manual operation, and large-capacity can choose electric switching. Molded case circuit breaker is to install contacts, arc extinguishing chamber, release and operating mechanism in a plastic shell. Generally, maintenance is not considered. It is suitable for the protection switch of branch circuit. The overcurrent release has thermal magnetic There are two types of thermal-magnetic molded case circuit breakers, the general thermal-magnetic molded case circuit breaker, which is a non-selective circuit breaker, with only two protection modes: overload long-time delay and short-circuit instantaneous protection. Electronic molded case circuit breakers have overload long-time delay and short-circuit short-circuit protection Four protection functions of time delay, instantaneous short circuit and ground fault.
What is an air circuit breaker?
Air circuit breaker, also known as air switch, is a type of circuit breaker. It is a switch that automatically opens whenever the current in the circuit exceeds the rated current. Air circuit breaker is a very important electrical appliance in low-voltage power distribution network and power drag system, which integrates control and various protection functions. In addition to contacting and breaking the circuit, it can still protect the short circuit, severe overload and undervoltage of the circuit or electrical equipment, and can also be used to start the motor infrequently.
Under normal circumstances, the armature of the overcurrent release is released; once a serious overload or short-circuit fault occurs, the coil connected in series with the main circuit will generate a strong electromagnetic attraction to attract the armature downward and open the lock hook. Open the main contact. The work of the undervoltage release is just the opposite. When the voltage is normal, the electromagnetic suction attracts the armature, and the main contact is closed. In the event of a severe drop in voltage or a power outage, the armature is released to open the main contacts. When the power supply voltage returns to normal, it must be re-closed before it can work, which realizes the voltage loss protection.
Differences between MCCB and ACB
- The difference between breaking current: the load and current of the circuit breaker are higher than that of the air switch;
- The difference between supporting equipment: the equipment supporting the mechanism of the circuit breaker is more complicated than the air switch;
- Difference in voltage level: When the current is short-circuited, the circuit breaker can cut off its current. In the case of high-voltage electrical appliances, the two are different from each other, and they can still operate normally, and can withstand a larger load, while the air switch will only exceed a certain current. will automatically disconnect.
- Differences in function: The circuit breaker will automatically trip when the circuit is short-circuited. It is often used in large-scale circuits such as high voltage, and is used for power failure and power transmission. The air switch is often used in households and is suitable for use in small circuits for isolation and protection.
- Different protection methods: the air switch can quickly disconnect the circuit and perform reliable protection in the event of overload, short circuit, and undervoltage of the line and load. Molded case circuit breakers can automatically cut off the current after the current exceeds the tripping setting, and use a plastic insulator as the outer casing of the device to isolate the conductors and the grounded metal parts.
- Different application scope: Air switch circuit breakers use a certain contact structure to limit the current limiting principle of the short-circuit current peak value during breaking, which has a significant effect on improving the breaking capacity of the circuit breaker, and is widely used. Molded case circuit breakers are relatively poor.
- Different in terms of safety: the air switch circuit breaker has high safety. Molded case circuit breakers are slightly worse.
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