How to select MCB(miniature circuit breaker) ? | Rating of MCB | Application of MCB | Specification of MCB | Use of MCB | Types of MCB

 How to select MCB(miniature circuit breaker) ?

In this article we discuss about most important protection device called MCB. MCB is like avenger for electrical appliances and machine.

We have costly house hold appliances like refrigerator ,tv, etc. Every appliance have rated voltage and current ratings. At rated current and voltage it work normally.

When any fault occur in appliance or supply line access high amount of current flow and this current damage the appliance.

Hence, to control this damage caused due to the excess current flow, circuit breakers are installed.

Content:

• 👉 What is MCB ?
• 👉 Name plate rating of MCB
• 👉 How to select MCB ?
• 👉 Use of MCB.

👉 What is MCB ?

Miniature circuit breaker (MCB) is an electro mechanical protective device which protect an electrical circuit from short circuit and over load . It automatically turns off, when the current flowing through it exceeds  the maximum allowable limit. 

MCB is mount on 35mm DIN rail.

It is a protective device.

👉 Name plate rating of MCB:

Rated current capacity: 

Rated current capacity of MCB is maximum amount of current which can be flow through MCB.

Standard rating of MCB is 0.5A, 1A, 2A, 3A, 4A, 6A, 10A, 13A, 16A, 20A, 25A, 32A, 40A, 50A, 63A, 100A for MCB.

Rated voltage :

Rated voltage is the  normal Operating voltage of MCB. 240/415 V AC as shown in above fig.

For three phase use it is 415 V and for single phase it is 240V.

Breaking Capacity :

Breaking capacity can be defined as the maximum level of fault current which can be safely cleared. It is written as in numerals like in in example it is 10000. It means it 10000A = 10kA. Choose breaking capacity as per your fault level possible.

Energy Class: 

MCB normally work on current limiting feature. It means that it does not allow fault to get it’s peak and trip before that. 

But since there is some time consumed in tripping, fault current will create some energy which will exist in system. This energy is termed as let through energy. 

For efficient MCB operation it should be limited. On basis of amount of energy it is classified in class 1, class 2 and class 3. Here Class 3 is best which allows maximum 1.5L joule/second. This is being tested as per IS 60898.

No. of pole :

MCB available in SP - single pole, DP - double pole, TP - triple pole, FP - four pole.

Tripping curve :

It is important for you to know about the types of MCB trip curves to decide what type of MCB use for different appliances or machines.

The MCB trip curves, also known as current v\s time (I-t) tripping characteristic. There are about five different types of MCB, which are B, C, D, K and Z.

As shown in above fig C25 , here C indicate tripping curve and 25 indicate rated current.

➣B type tripping curve:

Type B tripping curve

The MCB with class B trip curve trips within 0.04 sec to 3 sec when the current flowing through it reaches between 3 to 5 times rated current. 

These MCBs are suitable for resistive load like cable protection.

➣C type tripping curve: 

Type C tripping curve

MCB with class C trip curve trips within 0.04 to 5 sec when the current flowing through it reaches between 5 to 10 times the rated current. 

Suitable Domestic and residential applications and electromagnetic starting loads with medium starting currents.

➣D type tripping curve: 

D type tripping curve

MCB with class D trip curve trips within 0.04 to 3 sec when the current flowing through it reaches between Above 10 to 20 times the rated current. 

Suitable for inductive loads like transformer, welding transformer, motor loads with high starting currents.

➣K type trip curve:

K type trip curve

MCB with class K trip characteristics trips instantaneously (less than 0.1sec) when the current flowing through it reaches between 8 to 12 times the rated current. 

Suitable for inductive and motor loads with high inrush currents.

➣Z type trip curve:

Z type trip curve

MCB with class Z trip characteristics trips instantaneously (less than 0.01 sec) when the current flowing through it reaches between 2 to 3 times the rated current. 

These type of MCBs are highly sensitive to short circuit and are used for the protection of highly sensitive devices such as semiconductor devices, control devices, electronic devices.

👉 How to select MCB ?

Now we know about the types of MCB, we should analyze that which type of MCB would best suit for our household device. 

Before choosing the type of MCB, it is essential to find out a few technical details. 

➣First, check what voltage and frequency with which the device functions, like if it is AC or DC. 

➣Next, we decide the rated current capacity , MCB rating has to be selected according to the total load connected to the home. For example if you have a total load of 2 kw in your house, the maximum current will be 10.5 amperes approximately, so better go for a 2 pole 16 amperes MCB , for a single phase 240volts supply.

➣Additionally, see if there are any extra features like a manual or automatic reset and about safety approvals. 

➣Sometimes, the operating conditions, like the temperature, corrosion and radiation, may contribute to choosing the correct MCB.

➣Although the current rating is the primary deciding factor, it is better to analyze other factors before investing in the MCB as it plays an important role in preventing electrical hazards at your place.

👉 Use of MCB :

Miniature circuit breaker (MCB) is an electro mechanical protective device which is use to protect an electrical circuit from short circuit and over load.

This is my view on How to select MCB(miniature circuit breaker) ? after reading many articles.

thank you. keep supporting. 

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