What is MCB?
MCB stands for Miniature Circuit Breaker. It is designed to switch off electrical circuits automatically if any fault occurs in circuits like overload, short circuits, etc. Traditionally, we used fuse to protect the device from the above-mentioned issues, and nowadays MCB replaced the fuse.
The MCB is an electromechanical device that protects the electric wires and electrical load against overload and short circuits, etc. MCB is easy to use and we can quickly restore the power supply.
MCB has a very less maintenance cost. The working of MCB is based upon a bi-metal respective concept that protects from overload current and short circuit issues.
How to calculate MCB rating for an application?
Size of MCB = (Number of device X Watt X Demand Factor)/ Volt
Circuit Breaker Size % and Amps Charts
The maximum safe current limit is 80% of the breaker rating with some motors excluded. Keep in mind that the size of the breaker should not exceed the maximum rated current of the cables and wires. Below is a chart showing the % of the breaker size’s maximum rated current for different types of load current.
| Load Type | Maximum Circuit Breaker size % of current |
|---|---|
| Resistive loads, Heat, Toaster, etc | 125% |
| Lighting Loads | 125% |
| Air conditioners And heat pumps | 175% |
| Welders | 200% |
How MCB is made?
MCBs are mainly designed single-pole models for single-phase circuits. The MCBs are packed in a case made up of fire-resistant and high-strength plastics. Plastic gives a very high melting point, low water absorption, low thermal expansion, and high load deflection temperature. The machine is equipped with an arc chamber consisting of various arc chambers (metal plates) held by the position of insulating material. Since the arc chute stack does not always have to surround the contacts, some designs provide an arc chute to move the arc into the arc chute. The thermal shutoff mechanism consists of a thermomagnetic device in which the thermal effect is provided by a bimetallic plate and in some cases a heater. The locking mechanism is activated by the deflection of the bimetallic strip. Therefore, the properties of bimetallic plates provide a certain delay in case of overload or short-circuit current. Low-resistance bimetals are used in high-current circuit breakers, and high-resistance bimetals are used in low-current circuit breakers. A heater can be placed around the bimetal to produce sufficient heat for very low current MCBs.
The magnetic release mechanism consists of a coil wound around a tube. This tube has a spring-loaded stem and movement of the stem activates the release mechanism. During high short circuit currents, the magnetic field generated by the coil overcomes the spring force holding the plug in place. Thus, the movement of the bullet activates the trigger. The coil consists of thin wire with more turns for low-rated circuit breakers and thicker wire with fewer turns for high-temperature circuit breakers. Depending on the required characteristics, the magnetic release is set by the manufacturer.
Parameters to choose MCB
- Tripping characteristics
- Breaking capacity
- Number of poles
Purpose of MCB
It protects from overload
In both small and large-scale companies, MCBs can provide a reliable safety system.
What is Fuse and advantages of fuse?
How Does a Circuit Breaker Work?
Under normal conditions, if the circuit current rating is lower than the circuit breaker rating, the circuit will operate normally and can be changed manually. In case of malfunction or short circuit, it will trip automatically when the current value exceeds the current of the breaker. In other words, it breaks the circuit at the main power supply. For example, a 30A circuit breaker will trip at 30A whether it is a continuous or non-permanent load. So we need to select 20-25% more current in the circuit breaker than the current flowing through cables and wires to the connected device. Using a 100A circuit breaker on a 30A circuit will not protect the circuit from short circuit currents and currents above 30A will not trip the circuit breaker and may burn or damage the device. This means that you must use the correct size circuit breaker for your device. The circuit breaker current must not be lower or higher and must be 125% of the circuit current.
Internal parts of MCB
Top 10 MCB Manufacturers
Top 10 MCB manufacturers are
- ABB
- Siemens
- Legrand
- Schneider
- Havells
- Finolex
- Eaton
- Orient Electric
- Hager
- C&S
Advantages of MCB
- Easy to restore the power supply
- Less maintenance cost
- High sensitivity than fuse
- It works quickly on overloading and under voltage.
Disadvantages of MCB
- Costlier than the fuse
- There is a risk of overloading the circuit with unqualified maintenance personnel than with parts removed.
What are replacements for MCB
Fuse, MCCB, RCCB, ELCB are the main alternatives of MCB
Fuse: Fuse is an electrical device that is designed as a current interrupting device that opens or breaks the circuit by fusing the element in the circuit when current exceeds a certain value.
MCCB: MCCB stands for Moulded Case Circuit Breaker.
RCCB: RCCB stands for Residual Current Circuit Breaker.
ELCB: ELCB stands for Earth Leakage Circuit Breaker