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MCB, the abbreviation of Miniature Circuit Breaker, is a kind of automated electrical switch of an electrical circuit. The main function of MCB is during an unusual network condition or electrical situation; it gets off, to stop the current flow in this electrical system.
MCB: Overview
MCB are generally used as a safeguard for homes to reduce excess electricity and electrical shocks. The huge capacity of MCB can handle a large portion of electricity. The main advantage of MCB is to ensure equal electric distribution among various electrical devices.
MCB: Definition
MCB or Miniature Circuit Breaker is defined as an automatic small switch that is operated by an overloaded electrical network. MCB is available between 0.5A to 100A. The short circuit rating indicates the level of work which is denoted by kA. For instance, a domestic MCB has 6kA whereas industrial firms need a 10kA fault level.
MCB: Classification
As per usages
There are six types of Miniature Circuit Breaker, which are used in various electrical appliances.
Type A: MCB trips off the circuit when current exceeds 2-3 times than actual flow. Type A is highly sensitive and is used in semiconductor manufacturing.
Type B: MCB trips off the, 3-5 times than actual flow. Type B is used in low inrush load, electronic and computer equipment, as it has a low surge current level. It controls and protects circuits against short-circuit and overload in big length cables in TN and IT. It is used for residential, commercial and industrial purposes. The operating time is 0.04-13 seconds.
Type C: MCB trips 5-10 times of full load current. It protected inductive and resistive loads with low inrush electricity flow. It is used in small transformers, fluorescent lighting, control devices, pilot devices and coils. The operating time is 0.04-5 seconds.
Type D: MCB trips off between 10-20 times. Type D is used in high inrush current flow, especially in commercial and specialist areas. For instance, X-ray machines, winding machines etc. The operating time is 0.04-3 seconds.
Type K: MCB trips off the, 8-12 times than actual flow. It is suitable for motor loads and industry high inrush power. K and D are designed for motor applications where paucity reaches fast and momentarily during the ‘start-up’. Type K has high sensitivity thermostatic bimetal trip and is used in auxiliary circuits, transformers etc. The operating time is <0.1 seconds.
Type Z: This type trips between 2-3 times of MCB for the full load current. It controls and protects over a long duration and weak overloads and also short-circuits. The operating time is <0.1 seconds.
As per the Tripping Mechanism
MCB has two divisions of trapping mechanisms.
Thermal Trip Unit: Thermal trip is based on bimetal matters, located behind circuit breaker trip bars. It is protected against overloaded power and varies inversely with the current.
Magnetic Trip Unit: Magnetic trip is based on an armature and electromagnet. It protects against short power circuits.
As per the Number of Poles
The types of poles that are supported by MCB are-
Single Pole (SP): SP MCB protects one single phase in a power circuit.
Double Pole (DP): It protects and switches between a neutral and a phase.
Triple Pole (TP): TP Miniature Circuit Breaker protects only three-phase circuits.
Three Pole with Neutral (3P+N): it protects all three phases and is Neutral as well.
Four Pole (4P): it is similar to TP and also it has a protective release for a neutral pole.
As per Trip Cures
The trip curve is a graphical representation, which is plotted between the tripping times or current curve and release current.
Type B: It is used in domestic appliances, where stitching surge is low, for instance, 10A devices can trip at 30-50A.
Type C: It is used in industrial and commercial applications, for instance, 10A devices can trip at 50-100A.
Type D: It is used in high inrush uses, for instance, 100-200A tripping for 10A devices.
Working Principle of MCB
MCB is used to protect electrical circuits in domestic and small-scale firms as an alternative to fusing. In the case of a short circuit, it creates a sudden rise of electricity, causing the tripping coil or solenoid’s electro-mechanical displacement of plungers. The plunger strikes a trip lever that causes immediate latch releases which open a circuit breaker. In case of overload protection, MCB has a Bimetallic strip that causes a circuit to open, when continuous overpowering flow occurs the trip gets heated and deflects by bending. Deflection releases a mechanical latch, which is attached to an operating mechanism.
MCB: Drawbacks
- Costly than fuse
- It has a risk of overloading the circuit that a layman cannot operate
Conclusion
It can be concluded that MCB as a protective device can break a circuit to save current due to overload and short circuits. In the modern-day, the use of MCB is getting more popular, as it has several advantages.
