Motor HP/Amps ?

A little OT but can someone explain why small electric motors are rated only in amps while slightly larger ones are rated in HP? My Dad is looking at buying a new bench grinder and is having trouble figuring out how to compare various models from Delta, Ryobi etc. He isn't going to be happy with the performance of the smaller ones but won't be happy paying for the larger ones. He's looking for an 8" grinder. Any thoughts on brands/models?
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Everything's rated in amps, it's just in larger motors where companies go to the trouble of publishing HP figures in addition. Of course, you also have to remember that lots of small or cheap tools are sold with inflated "peak HP" ratings. Basically meaningless in the real world.
746 watts (or a little over 6 amps) equals one US horsepower. However, you won't get that on this planet due to efficiency, power ratings, etc. I think it's along the lines of 10A to every HP in modern induction motors. More power out of universal (brush) types. Just use it as a basic guide to know that a 12 amp shop vac doesn't make 6.5HP, no matter what Sears says.
Baldor, Milwaukee, Dayton, Wisotta (sp?) are some of the best grinder makers. Pricy, though. Among the imports, Delta, Jet, and DeWalt are good. Ryobi and Sears (frquently the same tool) grinders get worse every time a new model comes out.
GTO(John)

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1 HP = 746 watts
If you want to have some fun with math, see: http://www.engineersedge.com/electrical_equations.htm
I think I would check around and see what has been doing the job for others rather than buy based on the numbers vs. $$.
Parts availability, customer service etc need to be included in the equation also.
DexAZ

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I could post the table from NEC article 430 but I amy already have the copyright police closing in ;-)
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