inverse time breaker

[mark henderson]

Were can I find the calculation formula for a inverse time breaker?
I am going for a re take of a test tommorow. One of the questions I had had to do with the size inverse time breaker I would install for a motor. I am having a hard time locating this. I have pretty well figured the others I had a hard time on.

Thank You
Mark

 

[iwire]

Check out 430.52 and Table 430.52 2005

 

[bob]

IF it is a motor, look at table 430.52

 

[mark henderson]

OKay Thank You iwire.

So If I had a 5 horsepower, 230 volt single phase motor and a 3 horse power, 230 volt single phase motor it would look like this?

5hp: 28 amps x 2.5 = 70
3hp: 17 amps x 2.5 = 42.5=45
the answer is 60 amp I dont get how to get that answer?

Mark

 

[bob]

See 430.24 and 430.62. 60 amps is the rating of the conductor not the OC device.
1.25 x 28 + 17 = 52 amps.