Circuit Breaker

Calculation for Miniature circuit breaker ( MCB ) sizing Example : We want install 1 unit single phase motor.full load ampere is 20 ampere. Power supply 240VAC,50 Hz

1) Ampere Rating ( In ) Formula : In = Iz + (0.25 x Iz) In = ampere rating

Iz = Load ampere

Calculation : In = 20 ampere + (0.25 x 20 ampere) In = 25 ampere@ 32 ampere * in market we cannot found 25 ampere of MCB,so we can used 32 ampere for our application. Refer the ampere rated in technical data for MCB from manufacture From the technical data,we selected the ampere rated for MCB is : 32 ampere

2) Short circuit breaking capacity ( If )

Formula : If = V / 0.276 (R cable) If = short circuit breaking capacity V = Voltage R cable = resistance cable ( 0.276 ) Calculation :If = 240 / 0.276 If = 870 ampere Fom the answer,we can decide to select rating for one ( 1 ) kA

3) Application type. From application,it state the single phase motor,so we can choose TYPE C for MCB.It forgeneral application and for small motor.Please refer the table below for MCB type for the application. * For more detail,please refer the manufacture Technical data / user manual or contact the supplier. ABB MCB Technical data

Determine current in amps. Divide the wattage by the voltage of the circuit, in North America usually 120 or 240, ie: An electric water heater 4500w / 240v = 18.75 amps. This is the approximate amperage the device requires. Derate the circuit. Multiply by 1.25, the National Electrical code requires protection at %125, ie: 18.75 x 1.25 = 23.43 amp circuit. 

continuously by multiplying the circuit breaker's rating by .8 to determine 80% of the rating (a 15 amp breaker can pass 15 x . 8 = 12 amps and a 20 amp is 20 x .8 = 16 amps). Do not connect loads that exceed this 80% calculated value.



Be sure the wiring you are attaching to this circuit breaker is the right size to carry the amperage. Minimum 14 gauge for 15 amp circuits and minimum 12 gauge for 20 amp circuits. This is important. The NEC (National Electrical Code) is published by the NFPA (National Fire Prevention Association) and that's not a coincidence!

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Be sure you use a circuit breaker that is the same brand as the panel box you are installing, otherwise no warranty. NEWTECH MCB SELECTION CHART

S.no

Appliances

Capacity/Approx. Wattage at 240 V Single Phase i) 0.5Ton-775 W

1.

Air Conditioners

5

C

ii) 0.75Ton-upto 1200 W

7.5

C

iii) 1 Ton-upto 1.5 kW

10

C

iv) 1.5 Ton-upto 2.5 kW

16

C

v) 2 Ton-split unit upto 3.5 kW

20

C

1.5

C

ii) 285 Ltrs.

2

C

iii) 400 Ltrs.

3

C

iv) 581 Ltrs.

5

C

2

C

ii) 1300 Watts (with heater)

7.5

C

iii) 1800 Watts (with heater)

10

C

iv) 2200 Watts (with heater)

16

C

6

C

ii) 1 H.P.

10

C

ii) 2 H.P.

16

C

6

C

ii) 2 KW

10

B

iii) 3 KW

16

B

iii) 6 KW

32

B

25

B

1750 Watts

10

B

750 Watts

6

B

1000 Watts

6

B

i) 165 Ltrs.

2.

Refrigerator

i) 300 Watts

3.

Washing Machine

i) 0.5 H.P. 4.

Domestic Pump Set

i) 1 KW Water Heater 5.

(Storage or Instaneous Geyser)

6. 7. 8. 9.

Current Rating of MCB Type of MCB (Amps.)

Cooking Range 4500 Watts Oven Cum Griller Oven Only Microwave Oven

10.

Electric Kettle 1500 Watts

11.

Room Heater

i) 1000 Watts ii) 2000 Watts i) 750 Watts 12.

10

B

6

B

10

B

5

B

7.5

B

Iron ii)1250 Watts

APPLICATIONS: B Type MCB • For protection of Resistive loads such as bulbs, heaters etc ,generally suitable for domestic applications. They may also be used in light commercial applications.

C type MCB • For protection of Inductive loads such as motors, air conditioners etc devices are the normal choice for commercial and industrial applications.

MCB Selection: 

The first characteristic is the overload which is intended to prevent the accidental overloading of the cable in a no fault situation. The speed of the MCB tripping will vary with the degree of the overload. This is usually achieved by the use of a thermal device in the MCB.



The second characteristic is the magnetic fault protection, which is intended to operate when the fault reaches a predetermined level and to trip the MCB within one tenth of a second. The level of this magnetic trip gives the MCB its type characteristic as follows: – ·



Type

Tripping Current



Type B

3 To 5 time full load current



Type C

5 To 10 times full load current

0.04 To 5 Sec



Type D

10 To 20 times full load current

0.04 To 3 Sec



The third characteristic is the short circuit protection, which is intended to protect against heavy faults maybe in thousands of amps caused by short circuit faults.

Operating Time 0.04 To 13 Sec



The capability of the MCB to operate under these conditions gives its short circuit rating in Kilo amps (KA). In general for consumer units a 6KA fault level is adequate whereas for industrial boards 10KA fault capabilities or above may be required.

D type MCB • For protection of Cables and highly inductive loads which have high starting current such as examples include large battery charging systems, winding motors, transformers, X-ray machines and some types of discharge lighting.