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Whether choosing a molded case circuit breaker for home wiring or industrial application, there are several factors that must be taken into account. This MCCB selection article covers these factors with aim to guide you to the right MCCB.
What is MCC Circuit Breaker?
First, it’s important to understand the meaning of MCCB. An MCCB is the shortened form for molded case circuit breaker, a type of electrical safety device designed to prevent overcurrents from causing catastrophic damage to electrical wiring and equipment.
MCCBs are commonly used in commercial, industrial, or even residential applications as a means of protection from electrical faults and overloads. A typical MCCB breaker is an electromechanical device that consists of thermal and magnetic tripping mechanisms housed in a molded plastic case.
The thermal mechanism responds to overloads by tripping the breaker when temperatures exceed a preset value, while the magnetic trip responds to short circuits by providing an immediate shut-off. After the MCCB definition, below is how to go about selecting one.
Because applications vary, proper MCCB selection is critical. Selecting the wrong MCCB can result in catastrophic failure, with the potential of serious injury to personnel during and overload or fault condition such as short circuit.
The right device will also mean many other things, such as installation convenience, long life and cost savings. Here, we compiled list of key factors that will guide you on how to select MCCB rating, trip unit type, and other features.
MCCB Frame Sizes
MCCB circuit breakers are available in various sizes, both in terms of capacity and physical dimensions. Mostly, MCCB frame sizes refer to the maximum amount of current in amperes that the device is rated for. The larger the frame size, the higher the current rating.
Manufacturers usually group these sizes into various categories and use specific letters to denote the different breaker families. For example, an MCCB frame size may represent several amp ratings for that category of breakers.
MCCB Current Rating
One of the most important MCCB selection criteria is the current rating. This is the amount of current (in amperes) that a circuit breaker can handle safely.
It’s recommended to choose an MCCB with a current rating that is appropriate for your application; otherwise, it may not trip when needed.
On the other hand, a lower MCCB current rating than required can result in frequent tripping or nuisance trips. Standard MCCB breakers typically have ratings ranging from a few to hundreds of amperes, although they can be customized as needed. These are also usually adjustable.
MCCB Voltage Rating
Equally important to consider is the MCCB voltage rating. This is usually the rated operational voltage, rated insulation voltage, or rated impulse withstand voltage. The working voltage is the maximum amount of voltage that an MCCB can operate in when conditions are normal.
The breaker must be able to handle the voltage of your circuit in order to ensure a safe and secure installation. Common MCCB voltage ratings include 230 and 240 VAC for single phase systems and 400 or 415VAC for 3 phase applications.
It’s important to note that the MCCB must be suitable for either AC (alternating current) or DC (direct current) systems, as these require different voltage ratings and other features such as arc quenching capacities.
MCCB Trip Unit
The MCCB trip unit today comes in two options: thermal-magnetic and electronic. A thermal-magnetic trip unit reacts to overcurrents by tripping the breaker when preset values are exceeded, while an electronic trip unit has advanced features such as adjustable current settings and other advanced functions.
The type of MCCB trip unit you select will depend on your application’s needs. If you’re looking for an MCCB that provides superior adjust settings and advanced features such as remote control options, then the electronic trip unit may be your best choice.
On the other hand, if your system is a simple installation, say a single-phase installation, then a thermal-magnetic trip unit may suffice. Only make sure that the MCCB nameplate details match the system requirements.
Utilization Category of MCCB
Different MCCB types are designed to suit different applications and loads. This is known as the utilization category of MCCB breakers, which determines how much current the device can safely manage.
Utilization categories range from B to D and Z, depending on the specific trip curve. Here is a list of the MCCB types by their tripping curve and utilization categories:
- MCCB Type B: Low levels of current and starting currents such as domestic heating or lighting and small motors.
- MCCB Type C: Moderate industrial or commercial application with inductive loads.
- MCCB Type D: High inrush current situations such as commercial and industrial motors.
- MCCB Type K: For applications with high inrush currents and high surge currents.
- MCCB Type Z: Highly sensitive to short-circuit faults and used for the protection of electronic equipment.
Understanding the application and type of load that you are working with will help ensure your MCCB selection is appropriate. Remember, each MCCB trip curve has its own characteristics, and needs to be chosen carefully for the correct application.
The MCCB mounting type is also an important factor to consider when selecting the right MCCB for your application. The mounting type will affect not only how you install the breaker, but also its overall performance and operation.
Common MCCB mountings include, fixed, plug-in, and withdrawable installation methods. Always check the manufacturer’s MCCB specifications before making a decision, as that is where you’ll find the breaker’s specific mounting requirements.
During your MCCB selection, it helps to compare prices from different vendors before making a purchase. Remember, it is not always necessary to buy the most expensive option; there may be cheaper options available with similar features that suit your application.
Keep in mind, also, that MCCB prices vary greatly depending on the type, size, and features you select. For instance, if you choose an expensive electronic trip unit with advanced features, then expect to pay more than for a standard thermal-magnetic trip unit.
If you’re buying your MCCB online, make sure to check the shipping and handling fees to get an accurate estimate of what you’ll be spending. This is especially important if you’re ordering in bulk or purchasing multiple breakers at once.
Finally, your MCCB selection process is not complete without considering the accessories you might need. Depending on your application, you may require additional parts such as auxiliary contact blocks and shunt trips for remotely controlling your MCCB. So, here, we compiled a list of the most common MCCB accessories:
MCCB Shunt Trip Coil
An MCCB with shunt trip means the device can be remotely operated, either manually or automatically. This accessory uses an external source of power to trip the breaker by applying a voltage to its terminals. It allows for remote circuit disconnection.
MCCB Auxiliary Contacts
MCCB Auxiliary contacts are additional contacts that can be used to control a circuit remotely. They are usually connected in series with the MCCB’s main contact and can be used to switch on/off, monitor current flow, or even provide feedback signals when the breaker is tripped.
MCCB Rotary Handle
An MCCB rotary handle is a mechanical device that’s used to switch the circuit on and off manually or as an on/off indicator. It’s usually attached directly to the MCCB and can be used with the panel door closed.
MCCB Mechanical Interlock
An MCCB mechanical interlock is a device that’s used to physically prevent MCCB that have been mounted together side by side from closing at the same time. This is especially useful for preventing their simultaneous connection to the load.
A motorized MCCB is an MCCB that’s automatically opened and closed with the help of a motor. This is typically used in applications where frequent on/off cycling is required, or when a remote control switch is needed.
MCCB Alarm Contacts
MCCB alarm contacts are additional contacts that can be used to signal when the breaker has tripped, allowing for remote notifications. This is especially useful for monitoring circuits and troubleshooting problems before they cause any major damage.
MCCB Under-voltage Release
The MCCB under voltage release is a device that helps to trip the breaker when the voltage drops below a certain level. This is useful for protecting equipment (such as motors) from low voltage conditions that may cause damage or malfunction.
Knowing how to select MCCB circuit breakers goes a long way in ensuring a safe and reliable circuit. By taking into account all of the above factors, you can make sure that your MCCB selection process goes smoothly and leads to a successful installation. Not only that, but also that you are getting the best protection product for your specified application.
- MCB Selection Guide: How to Select MCCB
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