Table 430.248

[hungry_for_knowledge]

Can someone explain to me how does the table 430.248 1/4 HP makes 5.8 Amp. on 115V

please correct me because I strongly beleive that I'm wrong

1/4HP motor
746W/4=186.5W

186.5W/115V=1.62A

what am I missing to reach 5.8A. beacuse the table show that for a single phase is not 1.62A

Thanks

 

[wwhitney]

You're missing the motor efficiency: 1.62A / 5.8A = 28% implied efficiency.

In other words, a 100% efficient motor could convert 186.5W of electrical input to 1/4 HP of mechanical output, and at 115V it would use only 1.62A. The NEC wants you to design the circuit for a worst-case efficiency of 28%.

Cheers, Wayne

 

[dkidd]

Also need power factor

 

[wwhitney]

Also need power factor

Yes, definitely I should have included that. I guess one could call power factor "current to electrical power" efficiency. And the typical quantity you'd call motor efficiency would be "electrical power to mechanical power" efficiency. The calculated 28% would be the product of the two.

Cheers, Wayne

 

[tortuga]

Can someone explain to me how does the table 430.248 1/4 HP makes 5.8 Amp. on 115V

I always remember 1/4 HP 115V thats the largest single phase motor you can have on a general purpose branch 120V circuit with other loads.