[AT] Old shop lathe motor-- motor questions for you "experts"

[Bustedtractor at aol.com]

There have been a lot of comments on the list related to the newer HP ratings 
on air compressors, etc. My friend worked for an OEM Mfr of air compressors 
that built units for several well-known brands. The production line would not 
apply HP ratings until they knew who the customer was. The numbers ranged all 
over the scale based on the specs that they were to meet. 

Some compressors are called 3HP and are provided with 120 volts, 15 amp power 
cords! This violates all of the laws of physics! A 1HP motor will draw 746 
watts per HP if it were 100% effiecient. They are more like 80% efficient in the 
smaller sizes, so the power draw would be more like 933 watts per HP. A 3HP 
motor in that case would draw 2800 watts, or 23 amps at 120 volts. There is 
another item called power factor that further increases the amp draw by a factor 
of about 1.2 to over 27 amps. The National Electrical Code states that a 
circuit is not to be loaded beyond 80% of it's rating. That would dictate that this 
3 HP motor would need to be placed on a 35 amp circuit, not 15 amps! There 
ought to be some "Truth in Advertizing" applied to these HP claims!

Will in MN