Determining Loads with HP

[Jim Horn]

What are the fomulas for determing amperage with single (120v and 208v) and three phases devices with known horse power.

Example: Amperage for 208v, single phase, 1 HP

Amperage for 120v, single phase, 2 hp

Amperage for 480v, 3 phase, 2 HP

 

[GeorgeB]

What are the formulas for determining amperage with single (120v and 208v) and three phases devices with known horse power.

Example: Amperage for 208v, single phase, 1 HP

Amperage for 120v, single phase, 2 hp

Amperage for 480v, 3 phase, 2 HP

There are none. With large (say over 10HP) 3 phase motors, full load current may be approximated by assuming a power factor of about 0.85 and converting power to watts (746 watts / HP) then using basic 3 phase formulas.

To calculate (determine) circuit protection, you go by the code tables. To select motor overload protection, you use the motor nameplate.

As obvious as it seems, different motors are optimized for different criteria, and the current will vary among a variety of motors at the same HP ... take a look at www.baldor.com for some pretty good support information.