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8 comments
Anonymous Poster

How to Calculate Line Amps to kW 3-Phase 380V

06/02/2010 1:59 PM

sir, our machine 380 volt 3 phase 60 hz ,line ampere 12 amps . how to calculate total ampere?

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Guru
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#1

Re: how to calculate line amps to kw 3phase 380 volt

06/02/2010 4:07 PM

How are you differentiating 'Line Amps" from "Total Amps"? Neither is a defined term in my opinion. Amps are amps.

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#2

Re: how to calculate line amps to kw 3phase 380 volt

06/02/2010 4:39 PM

Why not just look on the motor nameplate.

Do you want FLA or LRA?

Here in the USA the FLA is used to size electrical service. At least that's what my contractor does. And he's a BMOC.

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#3

Re: how to calculate line amps to kw 3phase 380 volt

06/02/2010 10:28 PM

ARE YOU TRYING TO FIND MOTOR VA? VA = VOLTS x AMPS x 1.732 =380V x 12A x 1.732= 7898 VOLTS AMPERES

WATTS = VA X PF

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#4
In reply to #3

Re: how to calculate line amps to kw 3phase 380 volt

06/03/2010 1:58 AM

Yes..indeed.

In normal cases, the motor rating plate will give you the rating for the voltage and current. By the time we have these info, the engineer should design the incoming breaker size (which subject to the starting curent of the motor) and to calculate power consumed by the motor (kW) for the purpose of calculating the Maximum Demand.

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#5

Re: how to calculate line amps to kw 3phase 380 volt

06/03/2010 3:45 AM

Just check first your machine name plate. The electrical data is written there such as;

1. Voltage rating single phase or three phase

2. FLA amperage rating

3. KW or HP rating

4. Frequency

5. Ambient temp

6. RPM

7. Power Factor(pf).

The ampere rating in the nameplate is the maximum current or full load current, or thats the overall total current. If your question is suppose two 3-phase machines operating in parallel of different Kw size rating, then add their amp load and get the total.

Gen Formula; P= Sqr root of 3(1.732) x V x I x Power Factor

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Anonymous Poster
#6
In reply to #5

Re: how to calculate line amps to kw 3phase 380 volt

06/03/2010 4:03 AM

So you say that before designing, we have to buy motor!!!! Noted and will comply.

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#7
In reply to #6

Re: how to calculate line amps to kw 3phase 380 volt

06/06/2010 9:21 PM

The NEC and other electrical codes have tables of the FLA for motors of various horsepowers (or kilowatts) and voltages. Using these generic values, conductors, fuses, and circuit breakers are designed accordingly, without needing to have the motor(s) on hand. The overload protection, however, is selected by the actual FLA on the motor nameplate, with some correction for temperature differences between the motor and the starter locations.

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Anonymous Poster
#8
In reply to #5

Re: how to calculate line amps to kw 3phase 380 volt

06/23/2010 3:01 AM

thanks for the info.

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