Compressor motor marked spl

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josoglory

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I am currently wiring a 208-240volt air compressor. On the motor where the horsepower should be is the acronym spl. The motor also says just simply 15amps. On the front of the tank in big letters is: 3.5 running horse power. The Unit came with a 250volt twist lock cord end. a. How do I size the O.C protection and conductors for this air compressor if there is no horse power given?B. Is a twist lock cord sufficent as a disconnect. The motor is thermally protected and there is an on off on the presser switch.
Thanks!:-?
 
if you interpolate 250.248, or estimate the flc using the value for 3 or 7-1/2, flc= approx. 22 amps

spl means split phase

hp = 3.5

conductors: if this was continuous duty(?) then conductor ampacity should be 125% x 22 = 27.5 minimum (430.22)


ocp: for an inverse time breaker (250% - 430.52), the breaker size would be
2.5 x FLA = 2.5 x 15 = 37.5 maximum

I'm guessing motor has internal overload/thermal protection ? if not, and if you're not using continuous, then these answers are wrong (?)
 
josoglory said:
I am currently wiring a 208-240volt air compressor. On the motor where the horsepower should be is the acronym spl. The motor also says just simply 15amps. On the front of the tank in big letters is: 3.5 running horse power. The Unit came with a 250volt twist lock cord end. a. How do I size the O.C protection and conductors for this air compressor if there is no horse power given?B. Is a twist lock cord sufficent as a disconnect. The motor is thermally protected and there is an on off on the presser switch.
Thanks!:-?
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SPL stands for Sound Pressure Level

Basic Motor Terminology and Theory

 
The marking "SPL" is a trick some manufacturer's like A.O.Smith use on their homeowner-grade air compressor motors. They'll advertise these as 5 horse air compressors, but that's "peak horsepower". The real horsepower is less than 5, so they put "SPL" in the horsepower spot on the dataplate for "SPeciaL".
 
josoglory said:
I am currently wiring a 208-240volt air compressor. On the motor where the horsepower should be is the acronym spl. The motor also says just simply 15amps.
Click to expand...

430-6(A)(1) "where the motor is marked in amperes, but not horsepower, the horsepower rating shall be assumed to be the corresponding to the value given in Table 430-248", that is 3 HP & 17A.

josoglory said:
...a. How do I size the O.C protection and conductors for this air compressor if there is no horse power given?
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Size the OCPD as per 430-52 & table 430-248: 17A x 2.50 = 42.5, use a 40A breaker and #8 THHN cu branch conductors 310-15, (building wire not NM or SE, these will need to comply with 334-80 & 310-15), the equipment grounding conductor is sized as per 250-122.

josoglory said:
B. Is a twist lock cord sufficent as a disconnect. The motor is thermally protected and there is an on off on the presser switch.Thanks!:-?
Click to expand...

Yes the cord cap can be used as the disconnect but it needs to be sized as per 430-110(A) 17A x 1.15 = 20A. If the motor is TP rated you will not have to provide OL protection.
 
Folks, as I understand it this is a factory assembly with a factory installed cord cap.

Match the cord cap and all will be well. :smile:


20 amp cord cap = 20 amp branch circuit

30 amp cord cap = 30 amp branch circuit

KIS = Keep it simple
 
LarryFine said:
Okay, but will a 20a breaker start the compressor?
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Yes, just like my 15 amp circuits have no trouble starting my "5 HP" 125 Volt vacuum I bought from the big box store. (Marketing Hogwash)

Regardless what other choice do you have?

I would not replace the cord cap with a larger one on UL equipment and I would not place a larger OCPD on a branch circuit supplying a receptacle.

There is no way I would have say a 50 amp OCPD supplying a 30 amp receptacle.
 
iwire said:
Folks, as I understand it this is a factory assembly with a factory installed cord cap.

Match the cord cap and all will be well. :smile:


20 amp cord cap = 20 amp branch circuit

30 amp cord cap = 30 amp branch circuit

KIS = Keep it simple
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So is this somehow exempt from 430-6(A)(1)? I don't doubt you I am wondering how/where is this code compliant.
 
tryinghard said:
So is this somehow exempt from 430-6(A)(1)? I don't doubt you I am wondering how/where is this code compliant.
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I believe Exception 3 is addressing that issue.
 
tryinghard said:
Size the OCPD as per 430-52 & table 430-248: 17A x 2.50 = 42.5, use a 40A breaker and #10 THHN cu branch conductors 430-22(A) & 310-15, (building wire not NM this will need to comply with 334-80), the equipment grounding conductor is sized as per 250-122.
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Oops, I mis-quoted above earlier to use #8's that is wrong.

If this motor really does meet the criteria of exception 3 to 430-6(A)(1) then #12's will work but I didn't understand this motor to include both the HP and FLA so I would provide 10's
 
Like Marc & Bob referred to, it's marketing hogwash. My understanding they rate the compressors at something like "0 pressure equivalent hp."
For converstaion the HP rating on the compressor has little to do with what you and I think of as horsepower (electric motor type). You will notice the motor probably does not say 3-1/2 hp, just SPL. So you have a approx 3/4 electric hp motor on a 3-1/2 air horsepower compressor
It's a sales method to sell you a "3-1/2 hp compressor" at 1/4 the price of a compressor with a 3-1/2 hp motor. :)

I believe you can refer back to P.T. Barnum
 
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Either way the only item really in question is the OCPD and it doesn?t change the branch or the EGC anyway, and I believe the 40A breaker is the same price as a 20A, so:
  • 40A OCP, breaker 430-52
  • #12 THHN cu branch, 430-22(A)(1) & 310-15
  • #12 cu EGC, 250-122
  • 20A disconnect receptacle 240V 3W, 430-110
 
tryinghard said:
[*]40A OCP, breaker 430-52
[*]#12 THHN cu branch, 430-22(A)(1) & 310-15
[*]#12 cu EGC, 250-122
[*]20A disconnect receptacle 240V 3W, 430-110[/list]
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How do you get around 210.21(B)(1)?
 
iwire said:
How do you get around 210.21(B)(1)?
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430-31 & 430-32(A)(2), the overload protection TP.

I'm grasping but it does look like this actually complies, otherwise I still don't see how can this motor complies with 430-6
 
tryinghard said:
430-31 & 430-32(A)(2), the overload protection TP.

I'm grasping but it does look like this actually complies, otherwise I still don't see how can this motor complies with 430-6
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Are you telling me someone goes out and buys an appliance with a 15amp cord cap, and they have to buy a larger breaker also?? :grin: :grin: :grin:
 
stickboy1375 said:
Are you telling me someone goes out and buys an appliance with a 15amp cord cap, and they have to buy a larger breaker also?? :grin: :grin: :grin:
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Well at least the NEC seems to; maybe it's a 250V 20A cap? :roll:
 
tryinghard said:
430-31 & 430-32(A)(2), the overload protection
Click to expand...

I don't see how either of those sections allows ignoring 210.21(B)(1).


When a motor is included in a listed piece of equipment you do not use the ratings from the motor, you use the ratings of the entire equipment.

I looked at my shop vac, in large letters on the front it says 3.0 HP.

Table 430.248 shows that a 3.0 HP single phase motor has an FLA of 34 amps.

Should I use a 40 or 50 amp circuit for it because of the 3.0 HP rating?

Or should I go with the UL tag that says 8.2 amps @ 120 volts?

IMO if we could see this compressor and it's markings things would clear right up. :) I believe we have a case of marketing BS.
 
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