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Dear sirs Can I know what is the Motor Circuit Breaker size for 1 hp motor and what is the Formula to calculate it?

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تم إضافة السؤال من قبل mustafa محمد صادق السيد , Electrical Engineer , rmc
تاريخ النشر: 2016/07/16
SAJIN THOMAS SABU
من قبل SAJIN THOMAS SABU , Automation Engineer , Microcontrol for Engineering and Control System

First we have to calculate the current for that

1) For three phase motor

I= P(W) / (Root(3) * Line to Line Voltage * Power factor).

2) For single phase motor

I= P(W) / (Voltage * Power factor).

Power Factor for motor will be8.5 to9.

So we have to select a Motor circuit breaker having current range in that value.

Muhammad Qasim
من قبل Muhammad Qasim , Senior Electrical Engineer , Energy Associates (SMC Ptv.) Ltd.

For a single motor, breaker should be 250% of the I full load i.e. if the rated full load ampere is 10 Amps then the breaker selection will be 25 Amps. 

 

Cases are different when there is a group of motors and/or air conditioning hermetic compressor motor's etc.

Zaheer uddin Raja
من قبل Zaheer uddin Raja , Accounts Supervisor , Pakistan International Airlines

Circuit breaker / fuse size should be between 115 and 125 percent of FLA.

FLA (full load amperage) is ampares consumed by the motor at full load / capacity. 

Sadeq Al-Abbad
من قبل Sadeq Al-Abbad , Performance Development Coordinator , HALLIBURTON Energy Services

l agree with sajin answer thanks for invitation

gunti divya
من قبل gunti divya

we have to find out the mcb range for protection first we have to find out the current ranging..for that

For 1Phase P=VIcosX 

     3 phase p= Root 3 vi cos X

For EX:

    1HP FOR 1phase motor to calculate the MCB range

             P=VI COSX                

                                     1HP=746& cosX=1

   substitute the values

         1*746=230*I*1

          I=3.2 amps

To calculate mcb range I/0.8

                               =3.2/0.8

                               =4 amps

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