Hello all.

240VAC motors being "overhead" rated : A 20 HP capable motor or a 10 HP capable motor or a 5 HP capable motor driving a machine that demands just 2 HP to perform well (elevator, pump, compressor, whatever...) will any motor fitted consume nearly the same power/energy 'X' ?

If the electrical supply is reduced to 120VAC instead for those 240VAC motors and the driven machine demand is still met performing equally fine, will any motor fitted consume nearly the same power/energy 'X' ?

Unlike internal combustion engines, there is little difference between lower HP electric motors and higher HP ones so far as energy use is concerned. Electric motors like running at full power and higher HP will mean more weight to move from a larger motor but those differences are small and almost entirely made up by less losses from heat and friction in that stronger motor.

58 minutes ago, npts2020 said:

Unlike internal combustion engines, there is little difference between lower HP electric motors and higher HP ones so far as energy use is concerned. Electric motors like running at full power and higher HP will mean more weight to move from a larger motor but those differences are small and almost entirely made up by less losses from heat and friction in that stronger motor.

Do you have a reference for this claim, as it is very far from my understanding?

In passing, I would have thought that comparing the design rotation speed of the motor against the design rotation speed of the driven equipment might have been a first step.

1 hour ago, sethoflagos said:

Do you have a reference for this claim, as it is very far from my understanding?

I should have added when running at or near full power. Misunderstood the original post but load is well below rated capacity of any of the motors suggested, so none are going to be particularly efficient.

In passing, I would have thought that comparing the design rotation speed of the motor against the design rotation speed of the driven equipment might have been a first step.

That's the usual method of predicting efficiency. Again, all of the suggested motors would easily handle the load but not be nearly as efficient as one rated slightly higher than that expected load. Apologies for not being clearer.

You can expect a motor designed to provide more power than you need to be physically larger than one designed for a lower power. The main losses for an eletric motor are friction, windage and iron losses. In general these losses increase with the physical size of a motor. I would suggest you choose a motor that can provide the power you need plus, perhaps, a little more for longevity and reliability.

One factor not yet mentioned is that the torque/speed characteristics are very different for electric motors as compared to internal combustion ones.

So one consideration is to know where you want maximum power.

3 hours ago, OldTony said:

You can expect a motor designed to provide more power than you need to be physically larger than one designed for a lower power. The main losses for an eletric motor are friction, windage and iron losses. In general these losses increase with the physical size of a motor. I would suggest you choose a motor that can provide the power you need plus, perhaps, a little more for longevity and reliability.

Not to mention the 180 A current the 10 hp option is likely to pull on starting.