What is MCB (Miniature Circuit Breaker) and How Does it Work

Herbert Post December 08, 2021 4 min read

Safety is a major consideration while selecting electrical equipment, appliances, or devices. Every equipment and machine at homes, offices, or factories need a well-established electrical system. Without it, electrical devices become vulnerable to damage from overloads and short circuits in the event of power fluctuations or high inrush currents.

Circuit breaker technology has advanced in recent years, and new techniques have been developed to curb power fluctuations and provide overcurrent protection. One such technique is the use of theMCB (Miniature Circuit Breaker). To get you started, we'll go over some of the basics in this article.

What is a MCB (Miniature Circuit Breaker)?

What is MCB (Miniature Circuit Breaker) and How Does it Work

MCBs are small electromechanical devices mainly used to protect circuits from overcurrent failures and ensure electrical safety in residences, offices, and industrial sites.

Most circuits now employ MCBs instead of fuse switches because they don't need to be replaced if an overload is detected. Unlike a fuse, an MCB operates as an automatic switch—opening and closing in the event of circuit fluctuations, providing increased operational safety and convenience without increasing running costs.

How Does a MCB (Miniature Circuit Breaker) Work?

There are two types of tripping mechanisms inMCB (Miniature Circuit Breaker):

  1. Thermal Tripping
  2. Magnetic Tripping

Thermal Trip Unit

What is MCB (Miniature Circuit Breaker) and How Does it Work

The thermal trip unit is made up of a bi-metal thermal device that triggers the activation of a circuit breaker with a delay, depending on the overcurrent value. Its purpose is to prevent overload currents.

In the event of an overload, the bimetal heats up and bends due to higher current flow. As a result, it moves the trip bar, which unlocks the breaker connections. The time it takes for the bimetal to bend and trip the breaker varies with the current. 

Magnetic Trip Unit

What is MCB (Miniature Circuit Breaker) and How Does it Work

The magnetic trip unit provides protection against a short circuit. It is made up of an electromagnetic device coupled with a fixed or adjustable armature.

The strong current flowing through the coils creates a magnetic field that pulls the moving armature towards the fixed threshold. Then, the hammer trip pushes the moveable contact open.

Types of MCB (Miniature Circuit Breaker)

MCBs are classified based on their tripping curves to suit different types of applications. The 5types of MCBs are as follows:

B Type MCB

Tripping Current:3-5 times the rated current

Purpose:Protecting the electrical circuits of equipment that does not cause surge current

Application:Mainly used in residential applications or light commercial applications where connected loads are primarily lighting fixtures and domestic appliances with mainly resistive elements

 

C Type MCB

Tripping Current:5-10 times the rated current

Purpose:Protecting the electrical circuits of equipment that causes surge current

Application:Used in commercial or industrial facilities where there is a risk of excessive short circuit currents. This includes small transformers, lighting, pilot devices, control circuits, and coils

 

D Type MCB

Tripping Current:10-20 times the rated current

Purpose:Protecting the electrical circuits that cause high inrush current, typically 12-15 times the thermal rated current

Application:Used in particular industrial/commercial facilities where current inrush can be very high; concerned equipment include transformers or X-ray machines, motors, power supplies, etc. 

 

K Type MCB

Tripping Current:10-14 times the rated current

Purpose:Protecting windings in motors and transformers and simultaneous overcurrent protection of cables. Also suitable for inductive and motor loads with high inrush currents. 

Application:Mainly used in commercial and industrial facilities that have circuits like motors, transformers, and auxiliary circuits

 

Z Type MCB

Tripping Current:2-3 times the rated current

Purpose: Protecting and controlling electronic circuits against weak and long duration overloads and short-circuits. 

Application:Mainly used in commercial and industrial control circuits with high impedance and voltage converter circuits, including highly sensitive semiconductor devices.

MCB (Miniature Circuit Breaker) plays an important role in the safe and efficient operation of all the electrical systems across households and commercial and industrial facilities. That is why using first-class circuit breakers is so critical.

Miniature Circuit Breaker Lockout Device 

So, now we know that MCBs are very simple to operate. They can be turned on and off even without notice, causing accidental shocks and injury. This happens when a circuit prematurely reactivates while maintenance or repair is being carried out in the area.

Using miniature circuit breaker lockout tagout devices can help avoid incidents like these from occurring in the first place. These devices work by isolating hazardous energy from the system, physically locking the system in a safe mode. 

Here are some of the most common types of miniature circuit breaker lockout tagout devices:

Miniature Circuit Breaker Lockout Device – Pin Out Standard (POS)

Miniature Circuit Breaker Lockout Device – Pin Out Standard (POS)
The Pin Out Standard (POS) design features inward-facing pins and a push-button mechanism for faster deployment. It accommodates up to 0.5” hole spacing and accepts 1 circuit breaker padlock. Its nylon circuit breaker lock body is also electrically resistant and impact-resistant. No need to use tools to install.

[Order here]

Miniature Circuit Breaker Lockout Device – Pin Out Wide (POW)

Miniature Circuit Breaker Lockout Device – Pin Out Wide (POW)

The Pin Out Wide (POW) design features outward-facing pins, excellent for locking out wider miniature circuit breakers. It has a push-button mechanism for faster deployment.

It also accommodates up to 0.8” hole spacing andaccepts 1 circuit breaker padlock. Its nylon circuit breaker lock body is also electrically resistant and impact-resistant. No need to use tools to install.

[Order here]

Miniature Circuit Breaker Lockout Device – Pin In Standard (PIS)

Miniature Circuit Breaker Lockout Device – Pin In Standard (PIS)

The Pin In Standard (PIS) design features inward-facing pins witha push-button mechanism for faster deployment. It has a 0.3" padlock hole diameter, while its nylon circuit breaker lock body is electrically resistant and impact-resistant. No need to use tools to install.

[Order here]

 

TRADESAFE is a trusted USA-based partner in Lockout Tagout. Every lockout tagout device we make is built to last and is compliant with government-mandated LOTO standards, which we adhere to in both the design and production process. At TRADESAFE, our top priority is to make every workplace compliant with OSHA safety requirements.

Find out more about TRADESAFE or shop your lockout tagout devices here.

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Author: Herbert Post

VP Global Compliance at Barron Short Companies LTD. Born in the Philadelphia area and raised in Houston in a family who was predominately employed in heavy manufacturing. Herb took a liking to factory processes and later safety compliance where he has spent the last 13 years facilitating best practices and teaching updated regulations


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