Calculating Single phase motor FLA

[perryallen]

My first post so go easy on me if this has already been discussed.

I understand how to calculate 3 phase nameplate FLA based on H.P., volts and P.F. and EFF.
HPx746/(Volts x 1.732 x Eff x Pf)

But, what about single phase? One reference I purchased had the following for calculating a 110V, single phase, .5(that's 1/2) hp motor, with an effeciency of 80 percent and power factor of 70 percent:
(.5 x 746 = 373) ? (110 x 2 x .08 x .70 = 123.2) = 3.0 amps

Notice the calculation shows a multiplier of 2 added to the calculation. It uses the same multiplier of 2 when the voltage is 220, single phase.

Does this seem right? My resulting FLA is far below the FLC from the tables, from 9.8A to 3A. I'm taking the Master in a week and I want to get this right.

Thanks for any input.

 

[david luchini]

I don't know where the multiplier of "2" comes from. I think if you remove the "2" you would have the proper formula.

 

[raider1]

Welcome to the forum.

Which reference are you using that has 2 in the formula for finding FLA. The 2 is used in single phase voltage drop equations to achieve the required distance (2xdistance 1 way)

The formula for finding single phase FLA is HPx746/ volts x eff x pf. This is based on Ohm's law of I = P/E

Chris

 

[perryallen]

Welcome to the forum.

Which reference are you using that has 2 in the formula for finding FLA. The 2 is used in single phase voltage drop equations to achieve the required distance (2xdistance 1 way)

The formula for finding single phase FLA is HPx746/ volts x eff x pf. This is based on Ohm's law of I = P/E

Chris

Which reference? One that I'm going to be getting a refund for! I found other errors in the answers to some of the questions. I bought an exam simulation program off of a website to help me prepare. I won't name it in the open forum.

I also bought Mike Holt's Journeyman and Master exams and found them to be a little too easy. I took the ICC Journeyman test in Allentown, PA last month, and passed ok, but it was way harder than Mike's exam. So, I thought I'd get a little more practice but quickly became concerned that I was getting bad information.

Thanks for the reply.