Teach me about hp-rated plugs

[Choirboy]

My garage build has stalled over the past few months as I work frantically to get my house winter tight after gutting it to the studs. As such, the shop currently has no electricity.
I was given an early "shop warming" present of a 60 gallon, 3.7hp air compressor from my father and brother ("Hey, now that you have a shop, we'd better get you tools so we can use your shop for OUR projects!!") just like this one:https://www.menards.com/main/tools-hardware/power-tools-accessories/cool-tool-and-great-gifts-sale/sanborn-60-gallon-vertical-stationary-air-compressor/p-1444439609007.htm;jsessionid=61D98C8B8DDC04437D5B44BA01EEA592.eklka-prodapp4-external-mcom

It doesn't list the amp draw, but if my math is correct the 3.7hp should be just under 12 amps.

I was planning on hardwiring the compressor to the shop (not like I could move that huge thing anyway!) but it would be nice to be able to use it a bit for some projects now, and I do have a generator with a 20amp 240v plug on it.
I figured I could just put on a 6-20r plug on the compressor and run it off the generator until I wire the shop, but when doing research I discovered there is such a thing as a HP rating for plugs, and I would need something like a 50 amp plug to get to a 3-4HP rated plug.

Can somebody explain to me the difference between the amp rating for a plug and the HP rating? What is the logic for having both?

 

[dr_clyde]

I have never heard of a HP rating, but I'm not an electrician. Amperage and voltage are what matters. Wire an outlet for 50 amp 240v service and that way it could be used for a welder or something else down the road.

 

[pault28]

I have never heard of a HP rating, but I'm not an electrician. Amperage and voltage are what matters. Wire an outlet for 50 amp 240v service and that way it could be used for a welder or something else down the road.

Dr. Clyde, I have nothing to ad for the original poster, but I do believe he is not talking about the circuit rating, but for a disconnect switch. I don't know the specifics but if something is hardwired to a circuit and it is a certain distance from the panel circuit breaker, there is supposed to be a disconnect switch in line. Those types of switches are rated for HP and are rated per the load they will see.

If he is just asking about the amperage, then what you said is totally correct...a 50AMP would be great for a future welder too but more than likely a 30amp will suffice for the compressor.

As far as I know the HP and amp rating are for two different things.

 

[Charles (in GA)]

I have never heard of a HP rating, but I'm not an electrician. Amperage and voltage are what matters. Wire an outlet for 50 amp 240v service and that way it could be used for a welder or something else down the road.

Plugs and receptacles are indeed horsepower rated..... some are not. you need a 50 amp receptacle and plug to handle 3 hp If I recall.

I think the OP probably does not have a "real" hp rating on his compressor. It would help to know the CFM/pressure specs of the unit, thats a pretty good indication of the actual hp the motor is producing.

Charles

 

[Choirboy]

I guess I wasn't clear. I'm thinking about temporarily installing a plug to my air compressor so that I can run it off of my generator. But, when researching this very thing, I came across an old gargejournal thread here:http://www.garagejournal.com/forum/showthread.php?t=150706
See post #9 and others refering to the "HP rating" of the plug.
So, then I did other research and found sites such as this, explaining different plugs and their uses, and also referencing the HP rating: https://frentzandsons.com/Hardware%20References/plugandreceptacleconfiguratio.htm

So, since I've never heard of a HP rating and how it differs from the amp rating of a plug, I was just wondering if anyone could explain it to me.

EDIT: Charles, you are correct in that I don't have the hp for the compressor, only the information in the specs page linked in my original post. It lists it as 3.7hp, but I am aware that for marketing purposes sometimes the HP ratings are inflated. I'm not home right now to see if the motor itself lists a wattage.

 

[zkling]

In short IIRC, the HP rating comes from a what if disconnected at worst case possible scinario. Where the arc could cause a dire condition such as welding the contacts together. By the books, that really should be on a 50amp 240v plug, but...It probably is around 2.5-3 real HP, ~15amp at 230v?

 

[dr_clyde]

Interesting. I guess I've never noticed a HP rating on the plug end. You learn something every day.