How do you test MCBs?

To test any type of MCB after installation, you will need a suitable portable voltage meter from a reputable manufacturer. Electricians also recommend manually inspecting the switching mechanism of MCBs before installation; typically, a greater degree of pressure is needed to open and close more reliable models.

Specifications matter more than brand when choosing different types of MCBs, so in theory, you can use any component that is compatible with a particular device. However, mixing brands in the same installation is not recommended as it makes testing less reliable and can invalidate warranties and installation guarantees.

Why are MCBs preferred over fuses?

Various types of MCBs serve a similar function to electrical fuses, which are designed to melt and thereby break a circuit if the current flowing through exceeds a designated limit. However, fuses can be less reliable than MCBs - the latter work better in lower voltage settings and do not require replacement after use.

What is the Difference Between MCBs and MCCBs?

Molded Case Circuit Breakers (MCCBs) have a very similar function to different types of MCBs, but they also have a higher capacity. MCBs are all sub-100-amp devices and are designed for low-voltage circuits, so their trip curves cannot be adjusted. By contrast, MCCBs feature adjustable trip characteristics, which means that they can be used with higher voltages – as much as 2,500V in some instances.

What is the Difference Between MCBs and ELCBs?

ELCBs (earth-leaking circuit breakers) use earthing as their primary method of controlling electrical current and preventing electrocution. They work by detecting any stray voltage on the enclosure of a device and then breaking the circuit if it exceeds a designated level. They perform a similar function to RCDs, but the latter detect stray voltage directly and so are now more favored by electricians. What’s more, various types of MCBs respond to large surges of current, while an ELCB primarily detects smaller leaks.

What is the Difference Between MCBs and RCDs?

Residual current devices (RCDs) are a different form of electrical safety equipment. While MCBs have a general function, RCDs are specifically built to protect against the frequently fatal risk of electrocution from touching exposed wires or incorrectly earthed parts of cables. They operate directly within electrical circuits to detect faults and cut off potentially hazardous currents. RCDs are also available in various types – types A, B, C, D, K, and Z. In the United States and Canada, they are known as ground fault circuit interrupters (GFCIs).

- Published May 15, 2024
- Last Modified Nov 13, 2025
9 min

A Complete Guide to Miniature Circuit Breakers (MCB)

What is a miniature circuit breaker (MCB)? Discover the different types of MCBs and their crucial role in electrical safety.

In any electrical system, it’s crucial to ensure safety. Protection devices such as miniature circuit breakers play a role in preventing electrical faults. This guide explains everything you need to know about an MCB, including the different types available and their functions.

What is the Role of an MCB in Electrical Safety?

What exactly is the meaning of MCB? MCB stands for miniature circuit breaker, an automatically operated electrical switch that protects a circuit from damage caused by excess current. For many electricians and homeowners in the Philippines, this device is commonly referred to as a “breaker”.

Unlike traditional fuses that need to be replaced after a single use, an MCB offers a modern, reusable form of protection. When a fault occurs, the breaker automatically trips, shutting off the power and safeguarding equipment and wiring.

Part of the broader family of more powerful circuit-breaking components, MCBs are widely used as isolating parts in residential, commercial, and industrial facilities. They automatically isolate a circuit during electrical faults such as overloads or short circuits. This immediate response prevents potential hazards like fire or electric shock, making the MCB an essential upgrade from older, less convenient safety measures. It also protects against equipment failure, ensuring the longevity of valuable assets.

Types of MCBs

Miniature circuit breakers can be categorized into different types based on their tripping characteristics, number of poles, and breaking capacity. Selecting the right MCB is crucial for electrical safety and system efficiency, as each type is designed for specific applications and fault conditions.

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MCB Types by Trip Curve

The primary distinction between different types of MCBs is their trip curve, which dictates the overcurrent threshold at which they will trip. In the Philippines, Type B is widely used for residential applications, while Type C is typically found in commercial, industrial, and light commercial settings

Let’s take a look at the differences between each primary type:

Type B

Type B MCBs are designed for the most sensitive applications. They will automatically trip when the current reaches three to five times their rated load, protecting against small surges.

This also makes them ideal for residential properties and light commercial spaces in the Philippines, where appliances and devices generate minimal inrush current. Common applications include protecting lighting circuits, sockets, and general-purpose home wiring from overloads.

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Type C

Type C miniature circuit breakers are built for environments where higher inrush currents are expected. They trip at a current of five to ten times their rated load, making them less sensitive than Type B and more suitable for commercial and industrial settings. They are commonly used to protect circuits for inductive loads, such as small electric motors, fluorescent lighting, and commercial air conditioning units.

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Type D

Type D MCBs are the least sensitive type, designed to withstand very high inrush currents. Tripping only when the current reaches ten to twenty times their rated load, these miniature circuit breakers are the ideal option for heavy-duty industrial machinery that can produce powerful surges upon startup. Typical applications include welding equipment, large motors, transformers, X-ray machines, and uninterruptible power supply units.

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MCB Types by Number of Poles

Miniature circuit breakers can also be categorized by their number of poles, which refers to the number of conductors they can simultaneously protect from a fault. This is a critical consideration in the Philippines, as it directly relates to the type of electrical system being used, from single-phase residential wiring to three-phase industrial setups.

Single-pole (SP)

A single-pole miniature circuit breaker is designed to protect just one live conductor in a single-phase circuit. When an overload or short circuit is detected, the breaker trips and disconnects the live wire. This MCB type is very common for household applications in the Philippines, such as protecting individual circuits for lighting, outlets, and small appliances.

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Double-pole (DP)

A double-pole miniature circuit breaker is a two-in-one breaker that protects both the live and neutral conductors in a single-phase circuit. Both poles trip simultaneously, ensuring that the entire circuit is isolated from the power source during a fault. In the Philippines, this type is essential for circuits that power high-load appliances, such as air conditioning units, water heaters, and washing machines.

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Triple-pole (TP)

A triple-pole miniature circuit breaker is specifically designed for three-phase circuits. It protects all three live conductors and trips all three poles simultaneously when a fault is detected in any one of them. This is crucial for maintaining the stability and safety of three-phase industrial electrical systems. In the Philippines, these are standard safety features in manufacturing plants and commercial facilities that rely on heavy machinery and equipment.

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Four-pole (4P)

A four-pole miniature circuit breaker is a specialized breaker for three-phase circuits that also includes a neutral conductor. It provides protection for all three live phases plus the neutral wire, tripping all four poles simultaneously. This type is used in industrial applications where neutral protection is required, such as in motor control and distribution panels.

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MCB Types by Breaking Capacity

Breaking capacity refers to the maximum short-circuit current that a miniature circuit breaker can safely interrupt without being damaged. Measured in kiloamperes (kA), this rating is crucial for ensuring the MCB can handle the high fault currents that can occur in an electrical system. Selecting the correct breaking capacity is also vital for electrical safety, as a breaker with a low rating may fail catastrophically during a high-current fault, potentially causing an explosion.

In the Philippines, the choice of breaking capacity depends on the application. For most residential and domestic installations, a 6kA MCB is the standard and provides sufficient protection. However, in commercial and industrial environments, such as factories, workshops, and commercial buildings, higher fault currents are common. Therefore, 10kA MCBs or higher are required to safely interrupt a short circuit and prevent significant damage to the electrical system.

Parts of an MCB

These primary components of a miniature circuit breaker work together to provide complete circuit protection:

Toggle Switch: This manual lever allows an operator to turn the circuit on or off. It also provides a visual indication of the breaker's status: on, off, or tripped due to a fault.
Thermal Trip Unit: This unit provides overload protection. It consists of a bimetallic strip that heats and bends when a sustained overcurrent flows through it, tripping the breaker.
Magnetic Trip Unit: This unit protects against short circuits. It contains an electromagnet that instantly activates and trips the breaker when a sudden, high surge of current is detected.
Contacts: These are the points inside the MCB that make or break the circuit. When the breaker is on, the contacts are closed, allowing electricity to flow. During a trip, they open to interrupt the current.
Arc Chute: A series of metal plates that quickly cool and extinguish the electrical arc that forms between the contacts when the circuit is broken, preventing damage.

How an MCB Works

The working principle of a miniature circuit breaker relies on two primary mechanisms: a thermal trip unit for overload protection and a magnetic trip unit for short-circuit protection. An overload occurs when a circuit draws more current than its rated capacity over a period of time. The MCB's thermal trip unit, which consists of a bimetallic strip, is designed for this. When a continuous overcurrent flows, the bimetallic strip heats up, bends, and physically triggers the trip mechanism, opening the electrical contacts and breaking the circuit. The greater the overload, the faster the strip bends and the quicker the MCB trips. For a short circuit, which involves a sudden, massive surge of current, the MCB uses its magnetic trip unit. This unit features a solenoid or electromagnet. When a short circuit current flows, the magnetic field instantly becomes strong enough to pull a plunger, which strikes the trip lever. This immediate action quickly opens the contacts, shutting off the power and safeguarding the circuit from a dangerous current spike.

MCB vs. RCCB/RCBO

While an MCB is designed to protect against over currents, two other critical devices, the RCCB and RCBO, are essential for comprehensive electrical safety. An RCCB (Residual Current Circuit Breaker) is a specialized device that detects ground faults, which occur when current leaks from a circuit. This type of fault can cause electric shock or fire. The RCCB monitors the current in the live and neutral wires, and if it detects a difference—indicating a leak—it instantly trips to cut off the power, protecting against electrocution. An RCBO (Residual Current Circuit Breaker with Overcurrent Protection) is a combined device that integrates the functions of both an MCB and an RCCB. An RCBO breaker also provides dual protection against over currents (overload and short circuit) and ground faults, making it a highly efficient and compact safety solution. In the Philippines, for optimal safety, especially in residential and small commercial setups, it's common to use a combination of MCBs to protect individual circuits and an RCCB at the main electrical panel to safeguard against ground faults.