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

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.

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.

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. 

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