Need a little assistance....

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  #1  
Old 05-05-13, 02:57 AM
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Need a little assistance....

I am wanting to purchase a 230v Single Phase 22amp air compressor, with the way my garage is wired i have a power cable coming from a 40amp circuit breaker going into an outlet in my garage that says its a 250v 50amp outlet that has a power wire going to another outlet that says its a 250v 20amp outlet. When i test em with my cheap analoge multimeter i see around 230-240v. Is it recomended to use those outlets with that air compressor? For safety reasons should i switch out the breaker to a 30amp or will the 40 be fine? am i going to need to replace the current socket with one that is rated at 230v and closer to 30 amps, would i be able to run it off the 20amp socket? thanks for any info. here is the compressor im wanting Shop Kobalt 5 HP 80-Gallon 155 PSI Electric Air Compressor at Lowes.com
 
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Old 05-05-13, 03:59 AM
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Change the breaker to 30 amps and install a NEMA 6-30R receptacle.
 
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Old 05-05-13, 05:11 AM
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The 50 amp receptacle was probably for a small welder, and you can remove it and replace both receptacles with the NEMA 6-30R's as Ray mentioned. I do have my compressor wired to a different 240 volt breaker than the other 240 volt equipment, since it has a mind of its own. You don't want to be powering a 5HP table saw when the compressor decides to kick on. Judicious use, or total removal of one of the receptacles may be in order.
 
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Old 05-05-13, 06:09 AM
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The 250 is the voltage class of the receptacle, not the actual voltage. It is just the nomenclature used for devices.
 
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Old 05-05-13, 08:25 AM
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The circuit is sufficient, but I'd change the breaker to a 2 Pole 60 amp for a 5 HP motor.
 
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Old 05-05-13, 08:46 AM
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Joe, why so large a breaker on a compressor motor rated 22 amps full load? Is that strictly for starting current?
 
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Old 05-05-13, 11:20 AM
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I am not an expert, but motors do need a lot to be started. I usually follow my old Square D motor calculator, but they have stopped putting them out since the same thing is now online.

Motor Data Calculator Instructions

For a 5 HP single phase motor, use #10 wire, 60 amp thermal breaker or a 40 amp dual element time delay fuse.
 
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Old 05-05-13, 11:29 AM
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Thanks, Joe, for the info.
 
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Old 05-05-13, 01:00 PM
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Single phase motors may use up to 250% of the full-load rating when sizing an inverse time ration circuit breaker. Most installations will NOT require a circuit breaker this large and the circuit breaker should only be large enough to allow the motor to start reliably under the worst conditions.

Since this is an air compressor and probably has a special duty "compressor" motor it will probably do quite well with a 40 ampere circuit breaker. Use #10 conductors and a 30 ampere receptacle. Eliminate the second receptacle.

Understand that in this configuration the circuit breaker is primarily for short circuit protection and the motor's internal overload device provides the overload protection. This is one of the few instances where it is acceptable to use a circuit breaker that is larger than normal for the specific wire size.
 
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