Different molded case circuit breaker types are designed and meant to serve different purposes, different fault conditions, and so on. As such, a proper evaluation of the system’s needs must precede every selection process. This overview of the MCCB types will serve as a guide to help you choose wisely.
Molded Case Circuit Breaker Definition
Before we can look at the different types of molded case circuit breaker, it’s good that you understand what they are and how they work.
A molded case breaker is a type of electrical switch that is installed in industrial, commercial, and residential power distribution systems for the purpose of protecting against short circuits and overloads.
- It works by using a magnetic field to detect fault conditions. When the current reaches or exceeds a predetermined value, the electrical contacts will open and break the connection, stopping the flow of electricity before any damage can occur.
- An MCCB circuit breaker will often use a thermal part for the tripping mechanism alongside the magnetic one. In this case, a bimetallic strip will expand when heated due to current flow, causing the contacts to open and provide delayed tripping to overloads.
Molded Case Circuit Breaker Types
After the molded case circuit breaker definition, let’s now look at some of the different types the device available. The MCCCB classification is generally based on their trip curves. The most commonly used standard trip curves are B, C, and D. Others are type K and Z.
MCCB Type B
These molded case breaker types are meant to trip if they detect a current 3-5 times higher than what they are rated for, usually within 0.04 to 13 seconds, dependent on the rating of the breaker.
They are also normally installed on the distribution boards of industrial and commercial buildings with low fault currents. The B type MCCB is best used with resistive loads. These include lighting, heating, etc.
MCCB Type C
These types of molded case breaker are built to trip at fault currents that are between 5-10 times the rated current, with durations of 0.04-5 seconds. As you can tell, these types of MCCBs show moderate sensitivity to both overloads and short circuits.
Use them in systems with motors and other inductive loads. These are mostly power distribution systems that are subject to moderate levels of surge currents.
MCCB Type D
In comparison to the previous two types, type D MCCB is has a higher tolerance to fault currents. It trips at between 10-20 times its rated current, which is quite high, and for between 0.04 and 3 seconds.
This type of breaker is suitable for systems with high inrush currents such as electric motors or transformers and is usually installed at the incoming panels. As such, it best fits industrial applications.
MCCB Type K
The type K MCCB is specifically designed to trip when the current reaches between 8-12 times the rated value and for 0.04 to 5 seconds. Its best applications are similar to those of the D-breaker type: inductive load with very high inrush currents.
So it’s mostly used in industrial and commercial power systems. In these applications, the breaker protects circuits that incorporate motors, pumps, and relatively large transformers.
MCCB Type Z
These molded case circuit breaker types trip when they detect current values between 15-20 times the rated value and in a time range of 0.04 to 5 seconds.
These are specifically designed for short circuit currents, hence their high sensitivity rating. They are, therefore, well-suited for sensitive circuits such as computers or medical electronic systems.
- Molded case circuit breakers are also available in different pole configurations. These range from 1-pole up to 4-poles and include different voltage ratings for both AC and DC circuits.
- Each one of these has its own specifications, making them suitable for specific applications. It is always important to keep in mind the circuit rating before selecting a breaker type.
- The AC MCCB is the most common type and used in all kinds of low-voltage AC systems. The DC molded case circuit breaker is mainly used in solar power systems to protect against DC overloads and other DC circuit faults.
Molded Case Circuit Breaker Trip Curve
Since the above types of molded case circuit breaker devices are based on their trip curves, it’s only fair that we discuss it further. The trip curve of a molded case breaker is a graph or line chart showing the relationship between current and time on a circuit.
It demonstrates how long it takes for a molded case breaker to open when exposed to different fault currents, thus enabling you to determine if the device is suitable for your specific application or not.
- For instance, a type B MCCB breaker will trip at between 0.04 and 13 seconds when exposed to currents of 3-5 times its rated current.
- A type C MCCB, on the other hand, trips at between 0.1-0.4 seconds when exposed to 5-10 times its rated current.
As you can see, the molded case circuit breaker trip curve is essential in helping you determine which device to use for your specific application.
The wrong selection of the different MCCB types can be disastrous, so electricians always strive to make the right selection by understanding the trip curve of each, among other factors.
Molded case circuit breakers come in a variety of types. Every one of these types of MCCBs is designed to offer protection against different fault conditions and overloads. Understanding the functionality of each is the key to selecting an MCCB for your system. It will ensure that you choose a device that’s in line with your needs.
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