three phase current

hounddog

Member
H
Join Date
Jun 2003
Posts
79
have a question.
if you have a motor that you put a amp clamp on and it is pulling 28 amps across each phase, and is a three phase motor.

is the total current draw equal to 3*28, or is it 28 amps.

Does anyone know of a good web page with calculators, formulas, etc. to help with questions such as this.

thanks
 
hounddog said:
Does anyone know of a good web page with calculators, formulas, etc. to help with questions such as this.
Click to expand...

This is basic electrical theory. While it is possible, there is no practical reason to combine the individual 3-phase line (or phase) currents to come up with a single number.
 
Originally posted by wescEngineer:

Current as labeled on the motor should be around 28 amps but power is (3)^1/3 * V * I * Eff * Pf (units in watts).
Click to expand...

I'm pretty sure the equation should be:

31/2 * V * I * Eff * PF

as opposed to

31/3 * V * I * Eff * PF

as listed above.

Keith
 
kamenges said:
I'm pretty sure the equation should be:

31/2 * V * I * Eff * PF

as opposed to

31/3 * V * I * Eff * PF

as listed above.

Keith
Click to expand...

It is, another way to display is the square root of 3 (1.73)*V*I*EFF*PF
 
kamenges said:
I'm pretty sure the equation should be:

31/2 * V * I * Eff * PF
Click to expand...

That would be the mechanical energy output of the motor, accounting for energy inefficiencies.

The energy consumption of the motor is
31/2 * V * I * PF
 
First lets note that the square root of 3, which is used with 3 phase calculations, is 1.73

To obtain watts it is 1.73*V*I*PF, to obtain KW divide that by 1000.

To get HP (output) you use 1.73*V*I*EFF*PF divided by 746

As mentioned the formuals are shown here: http://www.patchn.com/motorformula.htm

V and E are both used to express voltage.
 

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