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I once read that a 3 HP motor was not possible to run on 120 volt circuit. Well, there are 15 and 20 amp circuits of 110 - 125 volts. By the way 110 through 125 is all the same, it's a standard wall receptacle. The average is usually stated as 120 volts, or so it is around here. Doing the math, 120 volts x 20 amps = 2400 watts. 2400/746 (1 HP) = 3.217 HP roughly, so yes a 3 HP motor is possible for a 120 volt circuit. Of course there will be losses, as no motor is 100% efficient, but how much, I don't know. At 85% efficiency, the output is just 2.73 HP, but you also sometimes get more than just 120 volts too, which will add to the overall number. I regularly meter 123 volts in my receptacles here at home, so I could see a possible 2 3/4 HP motor being ran on the output side of things. Also, this scenario assumes the 20 amp breaker is ran at maximum capacity, too. But there are also 30 amp breakers available as single pole breakers. Just use 10 gauge wire. So 3 HP is possible on single phase wiring, no 240 volts is needed. I didn't know where else to post this but in power tools so here it is. I'm just posting it because of what I've read in the past about 3 HP 120 volt tools not being true, and some of the various routers offered as 3 1/4 HP supposedly not able to be done. I'm not sure how manufacturers rate their products, either on input power or output, no load or under load, or what, but for those who don't know the math involved in figuring volts, amps, watts, and horse power, there's a bit of info for you. After seeing this, it makes me wonder why some people think 3 HP cannot be achieved on 120 volt circuits.
I also know someone will say this scenario isn't realistic, so here's one that is. Using 30 amp single pole breaker on 10 gauge wire, and loading the breaker to no more than 80% which is a recommended level, I get 24 amps x 120 volts = 2880 watts/746 (1 HP) = 3.86 HP. Assuming only 80% efficiency of a motor, which is awful, I'm still at 3.088 HP on the output side.
I also know someone will say this scenario isn't realistic, so here's one that is. Using 30 amp single pole breaker on 10 gauge wire, and loading the breaker to no more than 80% which is a recommended level, I get 24 amps x 120 volts = 2880 watts/746 (1 HP) = 3.86 HP. Assuming only 80% efficiency of a motor, which is awful, I'm still at 3.088 HP on the output side.