# motor question



## Tom45acp (Sep 6, 2011)

As far as I can tell, you're using nameplate amps for your single phase calculation and you're using Table 430.250 for a three phase motor. Table values are usually higher than the nameplate values.

If you use Table 430.248 for the single phase motor you'll get 8 amps x 230 = 1840 va


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## ampman (Apr 2, 2009)

Tom45acp said:


> As far as I can tell, you're using nameplate amps for your single phase calculation and you're using Table 430.250 for a three phase motor. Table values are usually higher than the nameplate values.
> 
> If you use Table 430.248 for the single phase motor you'll get 8 amps x 230 = 1840 va


yes i'am but that much difference in the single phase motors 4.5 a - 8.0 amps


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## JRaef (Mar 23, 2009)

ampman said:


> yes i'am but that much difference in the single phase motors 4.5 a - 8.0 amps


The NEC tables are only for sizing the circuit conductors and are based on worst case scenario, i.e. old energy hog motors. The nameplate is the real current draw, but that is irrelevant as far as sizing the conductors goes (unless the nameplate FLA was HIGHER than the NEC chart of course, but it almost never is).


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## Dennis Alwon (May 9, 2009)

If the motor is 115/230 then the amps should be 9/4.5 not 4.5/9. Not sure I understand the issue.


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## ampman (Apr 2, 2009)

Dennis Alwon said:


> If the motor is 115/230 then the amps should be 9/4.5 not 4.5/9. Not sure I understand the issue.


yea i got that backwards i guess i 'am trying to figure out how a 1hp motor can only draw 4.5 ampsat 230 volt


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## ampman (Apr 2, 2009)

JRaef said:


> The NEC tables are only for sizing the circuit conductors and are based on worst case scenario, i.e. old energy hog motors. The nameplate is the real current draw, but that is irrelevant as far as sizing the conductors goes (unless the nameplate FLA was HIGHER than the NEC chart of course, but it almost never is).


are newer motors that much more efficient


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## micromind (Aug 11, 2007)

According to my Leeson motor book, a 1 HP single phase premium efficiency model draws 4.2 amps at 230 volts. It shows 83% efficient. 

A basic standard one is 6.4 amps and 75% efficient. 

The 3ø model draws 3.2 amps at 230 volts and is 85.5% efficient.


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## Peewee0413 (Oct 18, 2012)

Three phase is more efficient


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## SteveO. (Oct 17, 2011)

The motor info seems fine, other than your reversal of the currents. Both voltages are single phase voltages and the efficiency seems inline with what should be expected. Either I'm missing what you're asking, or the info you posted is right as it should be. :blink:


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## Peewee0413 (Oct 18, 2012)

ampman said:


> A customer showed me a grainger motor (3rcx1) 115/230v - 4.5/9.0a 1HP now under 430.248 its 8.0 amps how are they rating this , also the rpm's differ 1725/1425
> 
> 4.5 x 230=1,035 va single phase
> 4.2x 230x1.732= 1,673va three phase
> ...


RPM difference is with 50/60 hz....?¿ 
Oh ya ....You might be missing a brain


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## Peewee0413 (Oct 18, 2012)

That's a single phase motor bro....not a three phase...why throw in the sqrt of pi


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## John Valdes (May 17, 2007)

In before the lock.


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## erics37 (May 7, 2009)

Peewee0413 said:


> That's a single phase motor bro....not a three phase...why throw in the sqrt of pi


It's the square root of three, dawg.


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## Peewee0413 (Oct 18, 2012)

Ha ha ...I wasn't sober last night.. Thanks for the smack in the face eric...


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## erics37 (May 7, 2009)

Peewee0413 said:


> Ha ha ...I wasn't sober last night.. Thanks for the smack in the face eric...


How you feelin today? Think of really greasy food. So greasy it's shiny, and it's sitting in a puddle of oil.


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