Know About Circuit Breakers - Part 2

A moulded case circuit breaker (MCCB) is an electrical protection device that protects an electrical circuit from excessive current caused by overload or a short circuit.

The MCCB is currently available with a rating of 16 A to 1600 A for general use and up to 2500 A for special needs. (Some companies are manufacturing up to 4000A.)

MCCBs can be used for different voltages and currents as they have adjustable settings available. An MCCB is a protective device that ensures safe and reliable operation in the long run. It is smaller in size than the ACB and is easier to maintain.

The moulded case circuit breaker (MCCB) can adjust the trip current according to the thermal or thermo-magnetic function, and also adjust the trip electronically.

The protection details provided in MCCB are given here.

The settings of common protection devices used in MCCB are described.

In this part, we will continue the protection details included in the MCCB.

Different manufacturers are providing their own protection devices applied in the MCCB.

In the Electrical panel, MCCB is used for branch circuits. MCCB is using the incoming and outgoing sections in SMB.

Here, explain the general settings, such as the thermal magnetic trip and the electronic trip unit provided in the breaker.

Thermal magnetic trip unit settings and electronic trip unit settings.

Thermal magnetic trip unit.

A flow of current that exceeds the rated current with a predefined time limit such a fault is called an overload. It is not a fault; it is only a condition.

MCCB has been classified into different types according to usage and tripping.

Type B.

They are operating at the fault current reaches 3 to 5 times the full load current.

It is used for domestic applications such as resistive loads, lighting loads, etc.

The available operating time of this breaker is 0.04 to 15 seconds

Type C.

This type of breaker is specially used for inductive loads, such as transformers, welding machines, electromagnets etc.

It has an operating range of 5 to 8 times the full load current with a time delay of 0.04 to 5 seconds.

Type D.

Suitable for heavy starting current applications such as motors, pumps, lifts, etc.

It has an operating range of 10 to 15 times with a time duration of 0.04 to 3 seconds.

An MCB is an automatically operated electrical switch.

Miniature circuit breakers are intended to prevent damage to an electrical circuit as a result of excess current.

They are designed to trip during an overload or short circuit to protect against electrical faults and equipment failure.

An MCB is designed to protect against both overloading and short-circuiting.

These are detected differently using separate processes.

Overload protection is provided by the bimetallic strip using thermal operation, whereas short-circuit protection is provided by the tripping coil via electromagnetic operation.

If the discharge is especially high, the MCB will trip (activate) very quickly – within one-tenth of a second.

International Standards, IEC 60898-1 and European Standard EN 60898-1, define the rated current of a circuit breaker for low voltage distribution applications as the maximum current that the breaker is designed to carry continuously at an ambient temperature of 40 °C.

Type B circuit breakers are designed to trip if the current flowing through hits between three and five times the rated load.

This is the most sensitive type of MCB, designed for domestic applications and low-voltage commercial settings.

Type C circuit breakers are used for more powerful electrical devices where any surges are likely to be higher, typically in commercial and industrial environments.

Type D MCBs are the least sensitive type, only activating when the current surges to between ten and twenty times the recommended maximum.

Earth Leakage Circuit Breaker - ELCB

Phase, Neutral and Earth wires of equipment are connected through ELCB while it is working based on the earth leakage current.

RCBO, Residual Current Circuit Breaker with Overload

This is a combined device of RCCB with MCB, so it comes with residual current with overload protection.

Residual Current Circuit Breaker - RCCB

RCCB is designed to detect the current difference between Phase and Neutral which is also known as Residual Current.

Residual Current Device - RCD

Generally, RCD is being used for RCCB, however, RCD is a generic term referring to any kind of device that automatically disconnects the circuit when residual current exceeds the specified limit.

A circuit breaker is an automatic switch that is designed to protect an electrical circuit from damages caused by excess current from an overload or short circuit.

Its basic function is to block the current flow after a fault is detected. Unlike a fuse normally used for this purpose, a circuit breaker is unique in that it can be set to resume normal operation once it has been activated.

All circuit breaker systems have common features in their operation, but details vary substantially depending on the voltage, current rating and type of the circuit breaker.

The circuit breaker detects a fault condition in the electrical circuit.

In low current circuit breakers, this is usually detecting within the device itself.

Typically, the heating or magnetic effects of electric current are employed to find the fault.

Circuit breakers for large currents or high voltages are usually with a protective relay device to sense the fault condition in the electric circuit.

Thermal expansion or a magnetic field also used in some circuit breakers to sense high current in the electrical circuit.

Small circuit breakers typically have a manual control lever to switch off the load or reset a tripped breaker, while larger units use solenoids or springs to trip the mechanism.