Breaking Down the Basics: Your Guide to Molded Case Circuit Breakers

Breaking Down the Basics: Your Guide to Molded Case Circuit Breakers

A molded case circuit breaker (MCCB) is a kind of protection device for electrical circuits. It works by preventing excessive current flow in the circuit thereby safeguarding the device it is connected to against risks like short-circuiting and electrical overload.

Let us get to know more about these crucial protection devices in this ultimate guide to molded case circuit breakers.

How does the MCCB work?

An MCCB combines a magnetic component (an electromagnetic device which is current sensitive) with a thermal component (a device sensitive to temperature). This allows the trip mechanism. Following this mechanism, the MCCB can provide

  1. Electrical fault protection against short-circuiting
  2. Protection against overloading, and
  3. Electrical switch for emergency disconnection.

Understanding MCCB features and ratings

All manufacturers of MCCBs are mandated to mention the operational features of the products they are offering. Some of the most common features of MCCBs are listed below:

  1. Rated Current (In): the tripping point of the MCCB during overload protection.
  2. Rated Frame Current (Inm): the maximum current that the device can handle. It determines both the frame size of the breaker and the upper limit of the rated current.
  3. Rated Working Voltage (Ue): the rated voltage for the constant use of the MCCB.
  4. Rated Insulation Voltage (Ui): the highest voltage that the MCCB can protect against in laboratory conditions.
  5. Rated Impulse Withstand Voltage (Uimp): This value represents the circuit breaker's ability to endure transient peak voltages resulting from switching surges or lightning strikes, thus determining its resilience against transient over-voltages.
  6. Ultimate Short Circuit Breaking Capacity (Icu): the maximum fault current value that the MCCB can withstand.
  7. Operating Short Circuit Breaking Capacity (Ics): The maximum fault current that the MCCB can withstand before being permanently damaged. The higher this value, the more robust the MCCB.
  8. Note that in case the fault current is more than the Ics but less than the Icu, the MCCB will still be able to operate. However, it will need to be replaced soon.
  9. Electrical Life: the maximum number of trips the MCCB can withstand before becoming non-operational.
  10. Mechanical Life: the maximum manual operations allowed before the MCCB fails.

Different Types of MCCBs

There are several molded case circuit breaker types available in the market, some of which are as follows:

  1. Type B: This type of molded case circuit breaker trips between 3-5 times the rated current. Tripping time is 0.04-13 seconds. These mostly have resistive, domestic applications and can handle low surge currents.
  2. Type C: These trip between 5-10 times their rated current. Tripping times fall within the range of 0.04-5 seconds. Applications involve relatively modest inductive loads, such as small motors, transformers, and electromagnets typically used in industrial settings. Suitable for higher surges.
  3. Type D: Type D MCCBs are known to trip between 10-20 times their rated current, and their tripping time ranges from 0.04 to 3 seconds. These MCCBs exhibit the highest surge tolerance and are thus selected for applications with extremely inductive loads like large electrical motors commonly found in industrial environments.
  4. Type K: These trip when the current reaches 10-12 times their rated current. Tripping time falls between 0.04 to 5 seconds. Applications involve inductive loads like motors.
  5. Type Z: Type Z MCCBs are the most sensitive among MCCBs, tripping when the current reaches only 2-3 times their rated current. They have the shortest tripping time and are employed for applications where extreme sensitivity is essential. This includes protecting semiconductor-based medical equipment and other costly devices that are susceptible to low current surges.

The Different Testing Methods for MCCBs

A common doubt regarding MCCBs is how to test the MCCB breaker. Three tests are essential and highly effective for this purpose and they are:

  • The insulation across load and supply terminals as well as between phases must be tested. This value should not be less than the insulation resistance value recommended by the manufacturer.
  • Testing the resistance of the electrical contacts is essential. The value should be extremely low.
  • Tripping tests have to be undertaken. Thermal power testing involves passing a huge current through the MCCB. If the MCCB does not trip, it is faulty. Magnetic protection capacity is tested by passing a very strong current in short pulses. Magnetic protection should be instantly achieved if the MCCB is working properly.

Read Also - 5 Differences Between Mcb and Mccb

Best Quality MCCBs Available at the Schneider Electric eShop

Now that you have a comprehensive idea regarding MCCBS, their types, what is breaking capacity in MCCB, and the steps for testing circuit breakers, you might want to scan the market for the best MCCBs suited to your project. When purchasing electrical equipment, it is best to opt for reliable brands to ensure complete safety.

For over two decades, Schneider Electric has been serving millions of customers with the best quality electrical equipment. The company is a leading manufacturer in the market for MCCBs. Browse through the range of MCCBs as well as other electrical equipment at the Schneider Electric eShop.

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