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Thread: Horse Power on a motor label

  1. #1
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    Horse Power on a motor label

    I was working with a compressor that has a motor with a HP rating of:

    SPL.00

    on the label.

    What in blazes does that mean? :confused:

    In case it matters its 230v. single phase, 15 amps.
    Sam, San Francisco Bay Area

  2. #2
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    Re: Horse Power on a motor label

    Probably for special. Compressor manufacturers who package compressors for home and light commercial duty play games with HP ratings which I haven't found to be true NEMA HP ratings. Just marketing.
    It's about the same as those shop vacs that have HP ratings on them.

  3. #3
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    Re: Horse Power on a motor label

    It's about the same as those shop vacs that have HP ratings on them.
    So you mean like my 120 volt, "Craftsman 5.5 Horsepower Compressor" with a 15 amp attachment plug? After removing the cover I found the motor label did not have a HP rating. The spot on the nameplate was blank. It did say 15 amps however. This would translate to about a 1 HP at 120 volts. A 5.5 HP at 120 volts would draw over 50 amps. And advertising this as a 5.5 HP isn't illegal?
    Rob

    Chief Moderator

    All responses based on the 2011 NEC unless otherwise noted

  4. #4
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    Re: Horse Power on a motor label

    I think that is EXACTLY why the motor label is blank. They are saying the entire tool is 5.5 HP. Not the motor. I believe under maximum load conditions, a 1 HP motor can produce up to 5 or so horsepower for a short burst. So the manufacturers are taking advantage of that fact and advertising the peak horsepower of the appliance rather than the NEMA Hp of the motor! It's all about marketing!!!
    Have yourself a great day!

  5. #5
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    Re: Horse Power on a motor label

    If you go to the big box, they have a "5 hp" air compressor that has a 15amp 125 volt cord.
    If you look in the NEC real 5 hp motor has a FLA of 53.

    [ March 01, 2006, 10:22 AM: Message edited by: tom baker ]
    Moderator-Washington State
    Ancora Imparo

  6. #6
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    Re: Horse Power on a motor label

    Perhaps they are taking credit for the horsepower that would be generated, briefly, at the moment of starting. If you multiply 120 volts times the starting current, and do a unit conversion to horsepower, you might get their numbers. But it sounds to me like a "truth in advertising" problem.
    Charles E. Beck, P.E., Seattle
    Comments based on 2014 NEC unless otherwise noted.

  7. #7
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    Re: Horse Power on a motor label

    Bingo Charlie, right on.
    Just a gimmick to satisfy our quest for more power.
    The only think that I use the rating for is to compare products assuming the 3hp is better than 2hp even though the rating doesn't mean a darned thing.
    When they refer to peak HP or "special" by whose rules are they playing by? There are no standards that I'm aware of. Is "peak" for a nano second?
    Dave

  8. #8
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    Re: Horse Power on a motor label

    So then I'm not crazy? SPL.00 is meaningless

    If I do the math I get:

    230v. x 15A. = 3450w.

    3450 / 746 = 4.625 HP

    I thought the nameplate was supposed to provide usefull information. :confused:
    Sam, San Francisco Bay Area

  9. #9
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    Re: Horse Power on a motor label

    Originally posted by physis:
    So then I'm not crazy? SPL.00 is meaningless...
    Well SPL is likely meaningless, but what does that have to do with you being crazy

    Originally posted by physis:
    ...If I do the math I get:
    230v. x 15A. = 3450w.
    3450 / 746 = 4.625 HP
    As noted by TomB, single phase motors are nowhere near to 100% efficient. NEC 430 shows a 230V, 2hp motor draws 12A


    Originally posted by charlieb:
    Perhaps they are taking credit for the horsepower that would be generated, briefly, at the moment of starting. ...
    I don't think so. I've never measured a single phase motor, but I suspect that the starting load is highly inductive. For example, at the instant of starting, the current is high, the voltage is still nominal, speed is 0rpm, it doesn't matter what the torque is, the hp output is zero.

    I've never seen the speed/torque curve for a 1ph motor, but as I recall (code phrase meaning I did not look it up) 3ph, Design B motor pulls out about 225% rated torque and 90% rated rpm, This gives about 2x rated hp.

    Nope, doesn't apply to vaccuum cleaners or compressors.


    Originally posted by ramdiesel3500:
    ... They are saying the entire tool is 5.5 HP. Not the motor. I believe under maximum load conditions, a 1 HP motor can produce up to 5 or so horsepower for a short burst. ...
    I don't think so. Motors run where the load/speed curve crosses the motor torque/speed curve. So vaccuums and compressors will never load the motor to the madison avenue rating.


    Originally posted by templdl:
    ... The only think that I use the rating for is to compare products assuming the 3hp is better than 2hp even though the rating doesn't mean a darned thing. ...
    I'm not even sure of that. I've got a small, light weight, industrial grade compressor I use for a framing nailer. Its 120V with a 15A cord, rated at 1hp. I don't think this particular one is lying. If I connect two nailing guns, and it runs constant, it will occassionally trip a 20A CB. I really doubt Sears best 5.5HP will keep up with it.

    If I had to pick one from the "big book" (or was it "box") - (in either case, yuck, ick, wash my mouth out, Bad Dog), I'd look at the free cfm, motor amperage, and tank volume.

    Originally posted by infinity:
    ... And advertising this as a 5.5 HP isn't illegal? ...
    Well if I said it in court, the junior engineers scoutpost would take away my secret decoder ring, break my slide rule, and make me eat a raw rutabaga. The court system would just call it lying.

    Madison Avenue likely calls it "Inovative, proactive, leading edge information transfer. Concept is supported by previously unknown new math techniques and computer generated fuzzy logic."

    carl
    Using the code for a design guide is a sign of incompetance

  10. #10
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    Re: Horse Power on a motor label

    Hi Carl, Good to see you again. :cool:
    Sam, San Francisco Bay Area

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