Air compressor plug....

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Yep. Code has exceptions for welder outlets where the breaker is sized larger than the receptacle (and the receptacle must be labeled Welder use Only). But not for motors. Either hope a 30A breaker holds and use a 30A receptacle, or use a 50A receptacle on a 50A breaker, or hardwire and use a 30A or 60A HVAC disconnect.

Motors and the NEC are a pain when there are many things with motor HP that don't match reality. Compressors and Sears power tools are two things that seem to have motor HP listed much higher than the nameplate amps would imply. Those marketing guys want to have the highest HP numbers possible, as that's what Joe Average looks at when buying a motorized tool.
 
Jamesco said:
FWIW nothing in the NEC says you can't install a single 6-50R (250V 50 amp receptacle on a 30 amp circuit that has #10 branch circuit wiring. It's true!:)

Problem is though the Leviton 6-50 Industrial Grade Extra Heavy Duty is only rated at 3hp.

5374 - 50 Amp NEMA 6-50R Flush Mtg Receptacle in Black - Leviton

Black - 50 Amp, 250 Volt, NEMA 6-50R, 2P, 3W, Flush Mtg Receptacle, Straight Blade, Industrial Grade, Grounding, Side Wired, Steel Strap
www.leviton.com www.leviton.com
Click on technical information



Yeah i figured a 30a receptacle seemed a little safer than a 50a receptacle because of conductor sizing, but I want to do it right. I should set a discconect with adequate voltage, hp rating and amperage also find a ul listed enclosure with a contactor and overload relay with a auto off switch? Most re air compressors I have hooked up have there own controller and enclosure... the control voltage is ran through oil and airpressure switch...
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suemarkp said:
Yep. Code has exceptions for welder outlets where the breaker is sized larger than the receptacle (and the receptacle must be labeled Welder use Only). But not for motors. Either hope a 30A breaker holds and use a 30A receptacle, or use a 50A receptacle on a 50A breaker, or hardwire and use a 30A or 60A HVAC disconnect.

Motors and the NEC are a pain when there are many things with motor HP that don't match reality. Compressors and Sears power tools are two things that seem to have motor HP listed much higher than the nameplate amps would imply. Those marketing guys want to have the highest HP numbers possible, as that's what Joe Average looks at when buying a motorized tool.
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Would you use #10 on a 50amp breaker and a 50amp receptacle. I know it’s dafefor the compressor but If someone comes and plugs equipment that pulls 45amps into the 50amp receptacle fed with #10 that seems potentially dangerous to me...
 
I don't believe code would allow that, except for some welder situations. A 50A breaker requires a conductor with 50A ampacity. So possibly #8 if the receptacle is 75C rated. A 50A receptacle on #10 wire with a 30A breaker is code legal. Yes, if someone comes and plugs a 50A appliance into that 50A receptacle, the breaker will trip. Code allows a receptacle equal to or larger than the circuit rating on an individual branch circuit. You could put a sign by it "30A max" if you wish. If I'm going to the trouble to run a circuit, I'd run at least #8 as the cost difference isn't that much and use a 30, 40 or 50A breaker.
 
suemarkp said:
I don't believe code would allow that, except for some welder situations. A 50A breaker requires a conductor with 50A ampacity. So possibly #8 if the receptacle is 75C rated. A 50A receptacle on #10 wire with a 30A breaker is code legal. Yes, if someone comes and plugs a 50A appliance into that 50A receptacle, the breaker will trip. Code allows a receptacle equal to or larger than the circuit rating on an individual branch circuit. You could put a sign by it "30A max" if you wish. If I'm going to the trouble to run a circuit, I'd run at least #8 as the cost difference isn't that much and use a 30, 40 or 50A breaker.
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I think I’m going to get away from the plug and receptacle all together... I’m going to run #10mc wire to a 60amp 1phase non fused disconnect and fuse it on on a 60 breaker or smaller... and hard wire compressor into the load side of the disconnect. that should be legal since it’s not a plug and receptacle. Conductors are sized per nameplate on motor, motor is thermal protected. And breaker is upsized for inrush... I want to use ten because I have #1 mc cable I can run instead of pulling 8’s through emt because I don’t have a helper...
 
ctaylo360860 said:
Would you use #10 on a 50amp breaker and a 50amp receptacle. I know it’s dafefor the compressor but If someone comes and plugs equipment that pulls 45amps into the 50amp receptacle fed with #10 that seems potentially dangerous to me...
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Would you use #10 on a 50amp breaker and a 50amp receptacle.
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No, not on a 50 amp breaker.


Well actually for figuring the branch circuit wire size you do not use the motor nameplate amps. You have to use the HP rating as found in Table 430.248. The nameplate on the motor says 5hp at 230V.
Using Table 430.248 says 5hp at 230V use 28 amps. 28 X 1.25% = 35 amps. #8cu wire.
Size of breaker at the panel, use a 40 or 50 amp breaker. Use the Leviton 6-50R receptacle. Pretty much what the electrician before you did.
 
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hillbilly1 said:
No, it is a 125/250 volt non grounding receptacle in the picture.
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I’m getting away from the plug and receptacle and just setting a disconnect...!
augie47 said:
I see a problem in that a 50 amp 240v plug (5-50R) is only 3HP rated and 430.109 requires cord & plug disconnecting be HP rated equal to the motor.
(Is it possible you could post a picture of the nameplate.. 22A for a 5HP does not match NEC Tables)
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image.jpg Name plate matches nec 430.248...
 
ctaylo360860 said:
Would you use #10 on a 50amp breaker and a 50amp receptacle. I know it’s dafefor the compressor but If someone comes and plugs equipment that pulls 45amps into the 50amp receptacle fed with #10 that seems potentially dangerous to me...
Click to expand...


Jamesco said:
No, not on a 50 amp breaker.


Well actually for figuring the branch circuit wire size you do not use the motor nameplate amps. You have to use the HP rating as found in Table 430.248. The nameplate on the motor says 5hp at 230V.
Using Table 430.248 says 5hp at 230V use 28 amps. 28 X 1.25% = 35 amps. #8cu wire.
Size of breaker at the panel, use a 40 or 50 amp breaker. Use the Leviton 6-50R receptacle. Pretty much what the electrician before you did.
Click to expand...

Edit:
The 3hp rated 6-50R receptacle still does not satisfy NEC.
 
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ctaylo360860 said:
I think I’m going to get away from the plug and receptacle all together... I’m going to run #10mc wire to a 60amp 1phase non fused disconnect and fuse it on on a 60 breaker or smaller... and hard wire compressor into the load side of the disconnect. that should be legal since it’s not a plug and receptacle. Conductors are sized per nameplate on motor, motor is thermal protected. And breaker is upsized for inrush... I want to use ten because I have #1 mc cable I can run instead of pulling 8’s through emt because I don’t have a helper...
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I like the idea of skipping the plug.
oldsparky52 said:
22 on the nameplate I would not call a match to 28 in Table 430.248
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Nameplate amps never match table 430
 
ctaylo360860 said:
#10 is good for 35Amps at 75 degrees so legally couldn’t I use #10 and put it on a 60a breaker? If not looks like I might have to run some pipe and pull 2_#8’s and an equipment ground in pipe to my dissconect...
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Look at 240.4 (D) (7)
#10 ampacity 30 amps.

Also look at 240.4 (G) & Table 240.4 (G) for overload protection.
 
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