Sump pump amperage and hp doesn't match nec chart

[ritelec]

Hello. Replaced a pump today.

The name plate was pretty messed up but didb notice it said 0.3 hp 115v 9.7 amps

I looked at the chart and the .5 hp was closer to that amperage

At the plumbing supply house the home owner and I picked up a zoeller 1/2 hp at 9.8 amps which matches the motor chart.

Still scratching my head on this I located the .3 hp motor on line

http://www.supplyhouse.com/Zoeller-...-115-V-03-HP?gclid=CPbH_47R38sCFdhahgodSWAIhA

Check specs on drop down. this is the motor I took out .3 hp at 9.7amps
Not the 7.2 amps like chart says for .3 hp

Why you think?

And kinda messes up using chart hp and ampacity theory for replacing motors

Thank you

 

[GoldDigger]

Given that the chart ((NEC) amps are based on the worst possible motor for that HP, I would not see it as any use as a replacement guide.

 

[jim dungar]

If it is 'special purpose' motor, not a general duty one, it may not need to follow the NEC values. This is how we get 40hp vacuum cleaners that draw 1A @120V.

 

[Carultch]

Given that the chart ((NEC) amps are based on the worst possible motor for that HP, I would not see it as any use as a replacement guide.

In this case, it seems the OP has found a counterexample where the "full load actual" is greater than the "full load code".

 

[kwired]

Given that the chart ((NEC) amps are based on the worst possible motor for that HP, I would not see it as any use as a replacement guide.

Yet he has a motor that is worse efficiency then the worst possible in the NEC tables.

This motor may not be in same classification as the motors in the NEC tables though, but is still a little surprising it draws more then the NEC tables. Maybe it is really a 1/2 hp design but for some reason only labeled 1/3 hp.

 

[ritelec]

Happy Easter


Thank you for the input

 

[drcampbell]

It's an oil-filled submersible motor. It takes a lot of power to churn oil; the 1/3-Hp rating might be shaft HP - what's available to turn the pump.

 

[kwired]

It's an oil-filled submersible motor. It takes a lot of power to churn oil; the 1/3-Hp rating might be shaft HP - what's available to turn the pump.

That is what motor rating usually is - output shaft rating.

 

[Smart $]

First sentence of 430.6(A)(1) starts...

Other than for motors built for low
speeds (less than 1200 RPM) or high torques...

...and goes on to say to use Tables.

Last sentence of 430.6(A)(1)...

Motors built for low speeds (less than
1200 RPM) or high torques may have higher full-load currents,
and multispeed motors will have full-load current
varying with speed, in which case the nameplate current
ratings shall be used.

 

[Jraef]

That is what motor rating usually is - output shaft rating.

Right.
HP = torque (in ft lbs) x speed (in RPM) / 5250 (a mathematic constant). No mention of Amps. The charts in the NEC are intended to allow for the proper selection of conductors feeding motors of a given HP. They have nothing to do with designing motors and what the FLC will end up at. GENERALLY, the charts are higher than most motors but there are exceptions and if you come across one, like this, you use the higher value.