Ratings and maintenance of MCCBs

We need MCCBs to save our electrical devices. Electrical circuits that are devoid of any MCCB are not fit for use. Such circuits lead to fire hazards and damage to electrical appliances.

MCCBs are resistive elements of an electrical circuit. They stand for Moulded Case Circuit Breakers. The sole function of MCCBs is to break circuits when excessive current flows through them. MCCBs protect the circuit from overloading and short-circuiting. 

MCCBs are available with several ratings that we need to know about. Here is a detailed list of those ratings along with their meanings.

What do the ratings of MCCBs mean?

There are several parameters and ratings for operating an MCCB. The following is a detailed list of the parameters along with their meanings.

  • Rated Frame Current:

The rated frame current determines the upper limit of the tripping current. It also states the maximum value of the overload current that the MCCB is meant to handle.

  • Rated Current:

This rating decides the tripping point of an MCCB to avoid any overloading. The rated current can be as high as the rated frame current.

  • Rated Insulation Voltage:

This value determines the maximum voltage at which an MCCB remains functional in ideal conditions such as labs.

  • Rated Working Voltage:

Rated working voltage is the optimal voltage required for the proper functioning of MCCBs. Its value is often the same as the system voltage.

  • Operating Short Circuit Breaking Capacity:

It is the highest fault current that an MCCB can withstand without being damaged. However, if the fault current exceeds this rated value, the MCCB may cease to remain effective. A higher value of this rating symbolises the greater effectiveness of the MCCB.

  • Ultimate Short Circuit Breaking Capacity:

When the fault current exceeds this value, the MCCB no longer trips at the point of overload. MCCBs do not remain functional once the fault current exceeds this rated value of current.

How to maintain the MCCBs?

MCCBs should be checked from time to time regarding their performances. It helps them to remain operative and useful for a long time.

There are several methods or tests to ensure routine maintenance of MCCBs. They are as follows:

  • Overload tripping test:

To keep the overload tripping components of the circuit breaker functioning at its best, apply 300 percent of the rated current to the MCCB. Note the tripping period for future reference.

  • Millivolt drop test:

A millivolt drop test is essential to detect any erosion in the contact points of the MCCBs. To perform this test, maintain a direct current of above 50 amperes for large breakers. Eroded contacts or loose connec­tions of the breakers are immediately brought into notice after the test.         

IndoAsian has an extensive collection of all types of Moulded Case Circuit Breakers to shop from. 


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