3 phase motors ratings

[trebor]

Hello you clever motor men

ive not had a lot to do with motors, what I would like to is if for example a 3 phase motor is quoted as 6kw (forgetting the kva and power factor for a mo) would it normally mean 6kw overall or 6kw per phase ?

 

[somersetsparks]

6KW overall, evenly distributed across all 3 phases.

 

[Guest123]

A 6KW rated motor is 6KW in total spread across all 3 phases.

 

[trebor]

Thankyou Lenny for the qick response, I would apprciate if you run your eyes over my calcs to see if I am on the right track, assumming a lagging power factor og 0.85 and 100% efficiency

kva = 6kw/0.85 = 7.05kva

design current Ib = 6000/1.732x400x0.8 = 10.83A per phase

In = say a 3 phase 16A Type D

Cable selection equal or more than 16A per phase

overload protection of the motor would be set within the starter

 

[Guest123]

The calc is sound.

Why though have you used a PF value of 0.8 in the calc when you say it is 0.85 in your first sentence??

 

[trebor]

The calc is sound.

Why though have you used a PF value of 0.8 in the calc when you say it is 0.85 in your first sentence??

thanks Lenny, a slip of the keyboard or brain there thanks for pointing it out

 

[Guest123]

Happens to us all bud.

 

[i=p/u]

just saying nice bit of maths, si can come bk to it when tutor throws a motor at me