Don't let that theoretical 800w per HP confuse you. Motors never get close to that efficiency. A typical 1HP motor will pull more like
12-13a @ 120v (my C/H compressor) and some cheap ones will be more like 15-16a.
Lowe's claims to have a 3HP electric chain saw, that still works on a
15A receptacle.
AFAIK that's some a not very useful rating called "peak horsepower" which I believe is the horsepower which can be delivered for a VERY brief time if the motor is up to speed and you suddenly apply a heavy torque load to it.
I think the energy must come from inertial storage in the rotating parts, but it gets "used up" pretty quickly and the motor HAS to slow down (and burn up?)
If someone has a better explanation, or a cite to an industry standard definition, I'm all ears.
Jeff
yep. $49.99 locally for the 200' rolls of 12/2wg NMB. I price it every time I go out (almost every day) as I have rentals that need wire and also my own house is still not quite finished in the wiring dept.
What type of fan? A box fan only has a 16ga wire on it. If it is rated for
12a. then that is probably the max draw on startup. 14 ga would do well, assuming romax, not extension cord. Still, why bother with 14 ga. Go with the standard 12 ga and put in a 20a breaker.
Assuming it's not simply a baldfaced lie, that is an intermittent rating. As in "if you load this motor with a brake to the point where it produces maximum output in overload, it's producing 3 HP - until the circuit breaker trips or the motor burns up, whichever comes first".
The rating might actually make a bit of sense for a chainsaw, where hitting a hard spot *will* cause the motor to put out more power temporarily, and where you're comparing against gas-powered motors where the HP rating is the maximum HP available.
But it's not comparable to induction motor ratings, where "1 HP" generally means it will deliver 1 HP all day, and nearly 2 HP momentarily when overloaded.
Rating continuous-running things like shop vacs and air compressors in "peak HP" is completely bogus, of course.
Dave
You must have a lot of rentals or they must use a lot of wire!
This reminds me of a friend at work who says his wife wants a lot of money:
"Every day my wife asks me for 200 dollars, every day!"
"Wow," I say, "What does she do with all that money?"
"I don't know. I never give it to her."
According to :
In case it wasn't clear, I wasn't confused ;-)
Once you get into multi-horsepower industrial-grade motors, rule-of-thumb is about 1000 watts per HP. At 1-2HP and below, they're not as efficient and 12-13A/HP is a reasonable ballpark at the high end. Once you get to 1/4HP and below, motors can be stupidly inefficient. Eg: the 1/4HP motor I saw whose label said 10A.
Yes. It's an instantaneous max HP, rather than a safe continuous rating. Shop vacuums and routers are infamous for using these inflated figures. Instantaneous max HP is a useful measure on a router or chain saw in some cases, but is useless to a shop vacuum.
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