There are many different MCBs out there, and choosing the one that is best for your project can be daunting. This MCB selection guide will help you find the right device or devices for your needs. We included the miniature circuit breaker specifications to look for, the different types of MCBs, and how to select the correct one.
What is an MCB?
A miniature circuit breaker or mini circuit breaker is a specialized type of electrical switch that’s designed to protect an electrical circuit from damage by overload or short circuit. Unlike a regular fuse, an MCB can be reset after it trips, which makes it much easier and faster to restore power to a circuit after an overcurrent event.
There are different types of miniature circuit breakers (MCBs) that are suitable for different applications. These offer varying levels of protection and can be selected according to the specific needs of a circuit.
During an MCB selection process, various aspects of these devices must be considered in order to find the best one for a particular application. These considerations are explained below
MCB Selection Guide
In this miniature circuit breaker selection guide, we will cover the most important factors to take into account when choosing an MCB. By the end of this guide, you will know how to select the right MCB for your particular application, whether residential or industrial. The considerations include:
MCB Current Rating
The miniature circuit breaker current rating should be selected according to the maximum current that is expected to flow through the protected circuit. If rated for a lower current, it will trip too often and cause unnecessary power interruptions.
On the other hand, if the MCB is rated for a current higher than necessary, it will not offer adequate protection in case of a short circuit or overcurrent. The MCB current rating is usually expressed in terms of amps (A). Typically, MCBs are rated for currents up to 125A
MCB Tripping Characteristics
These are MCB curve characteristics. They are basically indicative of the types of load the breaker is suited for. The main types of loads are: inductive loads (motors, transformers, solenoids, etc.), capacitive loads (buried cables, synchronous motors, etc.), and resistive loads (heaters, resistors, etc.)
MCB trip curves are usually classified according to the type of loads they protect. The main types of MCB curves are A, B, C, and D. Others include A, K, and Z.
- A-type MCB curves are designed for use with inductive loads, such as motors and transformers
- The type B MCB tripping curve is designed for resistive loads, such as heaters and lamps.
- The C-type MCB curve, on the other hand, is best for use with medium to high inrush currents, such as those seen with capacitive loads.
- D-type MCBs are designed for high inrush currents, such as those seen with motors and transformers. K-curve MCBs, too, suit these applications.
- Z-type MCBs are suitable for use in systems that do not need a high setting for short-circuit trip currents.
MCB Pole Types
The number of poles in a miniature circuit breaker indicates the number of live wires that the device can protect. The most common types of MCB poles are 1-pole, 2-pole, 3-pole, and four-pole.
A single pole miniature circuit breaker is used to protect a single live wire. These are the most basic type of MCBs and are typically used in residential applications.
A 2-pole MCB protects two live wires. These are more common than 1-pole MCBs and are mostly used in commercial and industrial applications.
A 3-pole miniature circuit breaker is used with three live wire circuits. Less common than the 2-pole MCB, this type of breaker will be mostly found in industrial applications.
The 4-pole MCB is used to protect four live wires. They are the least common type of MCBs but are sometimes used in very large commercial and industrial applications.
MCB Voltage Rating
This is the MCB voltage range. It indicates the maximum voltage that the device can safely be used with. The most common voltage ratings for residential MCBs are 240 volts (V) and 415 V. 240 V MCBs are designed for use in single-phase systems, such as those found in homes.
A 415 V MCB, on the other hand, is typically designed for use in three-phase systems, such as those found in commercial and industrial buildings. The voltage rating of an MCB must be equal to or greater than the nominal voltage of the protected circuit.
MCB Breaking Capacity
The interrupting capacity of a miniature circuit breaker is the maximum current that the device can safely interrupt. This is an important consideration during MCB selection as it indicates the device’s suitability for specific installations.
The MCB breaking capacity is usually expressed in terms of kilo amperes (KA). For example, a10kA miniature circuit breaker can safely interrupt up to 10,000 amperes of current. This capacity must be greater than the maximum expected current in the protected circuit.
Different miniature circuit breaker sizes fit different needs and applications. The dimensions of an MCB are typically expressed in mm. These must be appropriate for the application in which it will be used.
For example, an MCB that is too large may not fit in the available space, while an MCB that is too small may not have the necessary interrupting capacity for the installation.
There are a number of accessories that can be used with miniature circuit breakers. They include shunt trips, auxiliary contacts, and ground fault circuit interrupters (GFCIs).
But while these MCB accessories can be useful in certain applications, they are not always necessary. The decision to use them should be based on a careful analysis of the specific needs of the installation
Note also, that some of these accessories may not be compatible with all types of MCBs. Generally, higher-priced MCBs are more likely to accept accessories.
Miniature circuit breakers are electromechanical devices. Their life is, therefore, defined by the number of operating mechanical and electrical cycles that they can perform before they fail.
The expected MCB lifespan is, therefore, typically given as a function of the number of cycles. For the electrical life of a miniature circuit breaker, a minimum of 10 000 cycles is recommended, 20 000 cycles for mechanical life.
Miniature circuit breakers perform the crucial function of protecting electrical circuits from overcurrent. However, they can only do this if they are properly selected and installed. The selection of an MCB must, therefore, take into account the requirements of the application in which it will be used.
This miniature circuit breaker selection guide has outlined some of the main factors that need to be considered when selecting an MCB. Use them to make the right decisions for each parameter.