# Dealing with some motors coming from Overseas



## macmikeman (Jan 23, 2007)

http://calculator-converter.com/converter_metric_horsepower_to_kilowatt_hp_to_kw_calculator.php


You are welcome..


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## JRaef (Mar 23, 2009)

746W per HP.

kW/.746 = HP, which is (close to) the inverse of your 1.34102, but is easier to remember (to me).

So a 10kW motor is 10/.746 = 13.05HP, which isn't really going to help you much, except for sizing OCPDs and conductors, in which case you would use the charts for 15HP.

But there is potentially another problem. USUALLY, if the motor is rated in kW, it's going to be something like 400V *at 50Hz*. When you use it here on 480V at 60Hz, the motor works fine and provides the same torque, but the power rating, being based on torque and SPEED, actually goes up by the ratio delta of 50:60, so 120%. That means if your motor says 10kW @ 400V 50Hz, when you use it here, it is 12kW @ 480V 60Hz, so the HP is 16.01HP and you would have to use 20HP for the OCPD and conductor calcs. Sometimes though, the motor mfr will provide a 60Hz power rating and if so, use that.


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## tweak (Oct 3, 2010)

That's great macmikeman, but in section 430.6 A 2 it says that where a motor is marked in amperes (even though it is kW), but not horsepower, the horsepower rating shall be assumed to be corresponding to the value give in Table 430.247, Table 430.248, Table 430.249, and table 430.250. If we use your calculator you can see I had the correct multiplication factor and we get two different results for a 55 kW motor.

Your method gives us approximately 75 HP. Sizing per 430.250 gives me a full-load current of 96 amps.
The kW converted to amperage gives us a value of 66 amps.


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## JRaef (Mar 23, 2009)

tweak said:


> That's great macmikeman, but in section 430.6 A 2 it says that where a motor is marked in amperes (even though it is kW), but not horsepower, the horsepower rating shall be assumed to be corresponding to the value give in Table 430.247, Table 430.248, Table 430.249, and table 430.250. If we use your calculator you can see I had the correct multiplication factor and we get two different results for a 55 kW motor.
> 
> Your method gives us approximately 75 HP. Sizing per 430.250 gives me a full-load current of 96 amps.
> The kW converted to amperage gives us a value of 66 amps.


You don't calculate the FLA, you read it from the nameplate. The HP and charts are only for selecting OCPDs and conductor sizes.


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## tweak (Oct 3, 2010)

You are correct JRaef, my post should read



tweak said:


> That's great macmikeman, but in section 430.6 A 2 it says that where a motor is marked in amperes (even though it is kW), but not horsepower, the horsepower rating shall be assumed to be corresponding to the value give in Table 430.247, Table 430.248, Table 430.249, and table 430.250. If we use your calculator you can see I had the correct multiplication factor and we get two different results for a 55 kW motor.
> 
> Your method gives us approximately 75 HP. Sizing per 430.250 gives me a *current* of 96 amps.
> The kW converted to amperage gives us a value of 66 amps.


I guess the thing I don't understand is from this motor (manufactured in China) is the kW rating mechanical kW or electrical kW. If it's mechanical kW to HP the OCPD, conductors, heaters etc are going to have to be bigger than if the kW posted on my motor is electrical kW.

Thanks for the help.


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## macmikeman (Jan 23, 2007)

I got me a headache from that, and from not enough sleep....


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## John Valdes (May 17, 2007)

Just convert KW to HP and proceed as you would with any motor in your plant. KW x 1.34 is plenty good for what you are doing.
But you should heed the warning regarding voltage as these motors are not going to fit the general consensus for motor voltage in the US.
The Hertz or cycles will also most likely be different and should be considered.
In many cases today, motors are rated at 50/60 Hz and that should make things much simpler.

Should you have any motors rated for straight 50 Hz, I would just recommend you use them until they die.
I commissioned a machine once with a 75KW Chinese motor rated at 50 Hz.
That was 10 years ago and i hear its still running fine.


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## tweak (Oct 3, 2010)

All the motors are rated 480 Volt and 60 Hz.

I haven't seen them in person yet, just the cut sheets from our engineers with photos of the nameplate and wanted to make sure we got everything right on this one.

Thanks for the help guys.


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## micromind (Aug 11, 2007)

tweak said:


> You are correct JRaef, my post should read
> 
> 
> 
> ...


Nameplate KW is mechanical KW at the shaft. It translates directly to HP. 

Electrical KW will be less than nameplate at no load and more at full-load.

Edit to add; when I have to deal with motors that are marked in KW, the first thing I do is write the equivalent HP on the terminal box. Then the only thing I need from the nameplate is the full-load-amps for the heater size.


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## JRaef (Mar 23, 2009)

micromind said:


> Nameplate KW is mechanical KW at the shaft. It translates directly to HP.
> 
> Electrical KW will be less than nameplate *at no load* and more at full-load


Although true, for circuit sizing issues, forget the part about it ever being less than nameplate... you can't do anything with that value.

Electrical kW will be mechanical kW / efficiency. So if the nameplate says 55kW, and the efficiency is 80%, the electrical kW would be 55/.80 = 68.75 kW, in theory anyway. 

But there's some controversy on what the "Efficiency" number is based on. That's why you really can't calculate the electrical values from nameplate information. The "Efficiency" number they put on the nameplate (if any) tends to be "marketing centric"; the only REAL number they can't lie about is the FLA.


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