MCB  types B, C, D, K, Z, difference & Uses

Types of circuit breakers, miniature circuit breaker

        Hi friends, Today I will explain, difference between B, C, D, K, Z type MCB, (Miniature circuit breaker) and also uses of the MCB.

    

  There are 2 types of protection concept in MCB,

1)   Thermal

2)    Electromagnetic  

 

  The thermal trip is slow and used for overload current,

  The electromagnetic type MCB trip is fast and used for short circuit condition.

 

Difference between mcb types

 

 Thermal trip concept

  Difference between 5 types of MCB depends upon both the trip concept, Electromagnetic trip concept is more important for the difference in MCB types. The difference between 5 types of MCB, based on the thermal trip concept, 5 types of MCB are divided in 2 groups,

 

1)   B, C, D types

 

Range of trip current for B, C, D type MCB group, is from 1.13 In - 1.45 In, In is the nominal current of the MCB, If the current rating of the MCB is 10 amperes, then 1.13 In = 11.3 amperes, So 10A MCB, can trip anywhere in 11.3 - 14.5 A current range, as per thermal trip, if the rating is 100 amperes, trip range of current will be 113A to 145A, all 3 (B. C, D) types MCB, have the same trip range as per thermal trip.

 

 

2)    K ,Z types

    

    Range of trip current for K and Z type MCB, the trip current range is 1.05 In to1.2 In, for a 10A MCB, 1.05 In will be 10.5A and 1.2 In will be 12 amperes, means, If load current, is in between 10.5A and 12A range, then this MCB will trip, time of tripping will be different, it will take less time to trip at more current and more trip time for less current.

         if you take C type MCB rated for 10A, if current flowing is only 11 amp, then MCB will not trip, as the current is less than of this range, MCB will become hot and black and may burn.

 

 Electromagnetic trip concept      

  

     Now the  difference between B, C, D, K, Z type MCB, based on the electromagnetic trip concept, the magnetic trip is for short circuit current, I show here 2 In, 3 In, 5In, 10 In, 15 In and 20 In current levels, (In- means nominal current of the MCB), If MCB is 32 amp rating, then In will be 32 amperes, if current rating of MCB is 10A, then In will be 10 amperes, you tell current rating in the market to buy MCB, that itself is In,

      So, 2 In, 3 In, 5In, 10 In, 15 In and 20 In, if we take an MCB of 10A rating, the 2 In = 20 A, 2 times of In, 2 In means 2 times, 3 In means 3 times current, 20 In means 20 times current, so for 10A MCB, 2 In is 20, 3 In is 30A, 20 In will be 200 amperes, these 6 current levels will decide, the type of the MCB,

 

MCB types explained

 

1)   2 In – 3 In = Z Type MCB

2)   3 In – 5 In = B Type MCB

3)   5 In – 10 In = C Type MCB

4)   10 In – 15 In = K Type MCB

5)   10 In – 20 In = D Type MCB

 

     Now, 1st we discuss B type MCB The range shown for B type MCB is 3In to 5 In, this range is from 3 times to 5 times, for a 10A MCB, the trip current range is 30A to 50A if the short current flowing is from 3 to 5 times, of nominal current, and MCB is type B, then MCB will trip.

       Similarly, for a type C MCB breaker, the trip range is 5 time to 10 times or 50A to 100A for a 10A MCB,  If short circuit current flowing is in this range, then C type MCB breaker will trip, C type MCB can trip anywhere in this range, In some MCB, exact trip current is also indicated, if you take C type MCB and current is less than 5 times, then it will not trip, similarly, if we take 10A C type MCB, and current flowing is more than 10 times (100A), then it will trip, means, it will not trip below 5 times current, C type MCB, it can trip anywhere in 5-10 times current range, and MCB will always trip, for more than 10 times current.

      Similarly, the range for D type MCB, is from 10 times to 20 times of In, or range is 100 to 200A for 10A MCB, if the current is less than 10 times in D type MCB, then it will not trip, if short circuit current is in the range of 10-20 times, then It can trip at any current in the range, if the current is more than 20 times, then it will surely trip.

      The range is 10 to 15 times for K type MCB and for the Z type MCB the trip range is 2 to 3 times, Z type MCB trip at least current, then B type comes, the C type, then D and K type MCB, starting current range for D & K type is same, but the max value of the range is different, K type trip current range is close, D type MCB has a wider trip current range, So based on the magnetic trip concept, trip current (short circuit) decide, the type of the MCB,

      If we want that, MCB should trip in the range of 5 -10 time of In, then we should select C type MCB, if we want the trip range of the MCB, from 10 to 20 times of nominal current, then we should select D type MCB.

 

MCB types and uses , b- type mcb use

    

        Now B type MCB, of trip current range of 3 to 5 times is used in the following applications, it is used in the load having no surge current, starting (surge) current should not be there, for example, resistive load, B type MCB is used mainly in resistive load, like lightning, domestic appliances like, heater, electric iron etc.

      Uses of C type MCB (5 -10 In trip current range), C type MCB is used, if starting or surge current is more, surge current means, if we switch ON some load and heavy starting current flows during starting for some times,   

 

      like, motor, examples, low horsepower (HP) motor, small size motors, they are used for domestic appliances, like air conditioners, water pump, washing machines, Further power factor capacitor in the industry, uses C types of the MCB, whenever you start, AC or water pump or washing machine, and a normal AC motor is used, then heavy current flows, during starting for some time, current becomes less after some time, if that surge current, fall in the range of 5 -10In, then MCB will trip, now you will say that, if a motor is there, I will switch ON the motor, a surge current will flow, then MCB will trip, but it should not trip, else how we will use the appliances, then what we should do, we should know surge current of the motor, that surge current is should be less than 5 In of MCB selected.

      Now uses of D and K type MCBs, D & K are grouped together, because, D type has the range 10-20 times, K type MCB trip range is 10-15 times, both ranges are overlapped, but the range of D type is more, some places D type MCB is used, some places K type MCB is used, D type MCB is used for loads, with very high surge or starting current, D type MCB is used mostly in industry, some time load is pulse generating type, the pulse of very high current, D type MCB is used for transformer, with cables, the motor also draw more current during starting, but the transformer, may draw very heavy starting current, solenoid valve, battery charger, X ray machines, welding transformer, starting current is more in all these equipment, so D or K type MCB is used, if the close range is required, then K type MCB is selected and D type for a wide range,

      if surge current is in this range, then MCB will trip again and again, so MCB of proper rating is to be selected, based on the transformer size, if you are using C type MCB in your industry and that is tripping frequently, then try D type MCB, this is just one possibility, there may be many reasons, for MCB tripping.

     Uses of Z type MCB, tripping range of Z type MCB is, 2 to 3 time of nominal current, 20-30A for 10A MCB, Z type MCB trip at least current range, Z type MCB is used, in semiconductor circuit & control circuits, like thyristor rectifier, Mosfet power circuit, If the power electronics circuit is there, then semiconductor can’t take high current, then will fail, so they are tripped at less current itself,

     I told you that, B type MCB is used for resistive load, C type MCB is used for motors, resistive & motor both are used in homes, then we can use C type MCB.

 

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