Theoretically, 1 HP equals 746 watts. But that is a delivered power rating. That is the amount of power measured at the shaft. The amount of power to create it is always more than the delivered power....or you would have perpetual motion. This is all part of the Conservation of Energy Law thing. Some laws are made to be broken....this one can't be.
1HP motors are around 78% efficient, which means that they use about 22% more power than they deliver. So, roughly, a 1HP motor delivering 746 watts of power would use about 9-10 amps. With the start up load ( efficiency is much worse at slower speeds) 12 amps is about right.
Every wire, switch, control, V-belt, bearing, pulley, tensioner, grinding pressure, etc. in the path between the breaker and the piece of steel being shaped reduces the motor's delivered power more. These also raise the amps needed to run the motor. Lean in hard on a blade while hogging the bevels and you can pop a breaker or blow a VFD fuse.
When I see a $40 shop vac rated at 5HP I laugh. In an efficient motor that would draw 40-50 amps on a 120VAC line. What the manufacturers do is use a deceptive calculation they call "developed Horse Power" .... which is obviously a horse of another color.
Then there are the 3500RPM motors that are rated at what seems to be twice as much power as they deliver.....and the manufacturers who use the current drawn and rate the motor by the power consumed. By their deceptive rating, my 1HP Leeson that draws 12 amps would be a 1.75HP motor....which it is not.
Many of us remember when the car manufacturers used to calculate mileage theoretically.
They said: A gallon of gas has 44.4 Newton meters of energy, our car weighs 3000 pounds and has a 150HP engine. That means the engine delivers 111,900 watts of power, which means it can drive XX miles on one gallon of gas. Of course, when you drove it, it didn't get near that "theoretical" mileage.
Octane was calculated in a similarly deceptive "theoretical" rating. Eventually, the government passed laws that said the ratings had to reflect real "delivered" measurements.
These type statements can be true, and still misleading. CSX uses a false statement in their adds claiming their engines are so efficient they can move a ton of freight 450 miles on a single gallon of fuel. They arrive at that number by dividing the total millions of tons of freight moved a year by the total number of gallon of diesel purchased by the total miles of track driven. Actually, the engine would start and run out of fuel in a few a seconds on a "single gallon of fuel".
In truth, efficient diesel freight train engines burn several hundred gallons of fuel an hour and average 50MPH or less. They carry about 4000 gallons of diesel. Each locomotive can pull/push around 4000 tons. Two or three engines power a full freight train. That means it takes about 10,000 gallons of fuel to move a 10,000 ton train of freight 450 miles....but the math can be twisted to say so it sounds much better.
