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Electrical Wiring

240v Air Compressor Wiring

7 years ago

60 Gallon Husky with 3.7HP 230v motor. I haven't gotten around to looking at the wiring terminals. The manual is very vague and lacks any type of information relating to wiring. I just had the entire electrical system updated and had put a 100 amp GE panel in the garage so I can run this compressor I've had for months. The manual does state a minimum of 20 amps for the 2 pole breaker. Due to how an electric split phase motor can draw more than twice it's running amperage (13.7 amps) on start up, I am thinking that a 30 amp 2 pole is the best option with 10/3 Romex. Seeing as the motor will only draw the amperage it needs, or so i thought, would this cause any issues running a 30 amp breaker? My other question is, what type of receptacle and cord should I use?

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Comments (4)

randy427
7 years ago
You should be safe in using 12 gauge wire, but upgrading to 10 gauge won't hurt anything, but still use a 20 amp breaker. I'd hard wire the compressor with type MC cable rather than use a plug and socket, providing you intend to leave it in one place. You'll only need a 12/2 (or 10/2) cable, rather than 3 conductor, as the neutral is not normally used on a 230v motor.
User
7 years ago
A little info on HACR ratings and inverse time circuit breakers;

http://static.schneider-electric.us/docs/Circuit%20Protection/Molded%20Case%20Circuit%20Breakers/0600DB0102.pdf

.

https://www.schneider-electric.us/documents/support/codes-and-standards/circuit-breaker-markings-iaei.pdf

.

The 20 amp breaker should be fine. The problem most people have is with the lights dimming when the motor kicks in. That is caused by voltage drop, which is caused by too much amperage going through too small of a wire. 10 gauge wire can help this, but other factors may also effect this.
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OK- Here's what I've found. By the way, I was hoping to also use this outlet for a 240V welder I recently bought. I contacted Lincoln Electric for exact specs on the electrical service requirements today. Get this: My welder happens to have a current demand very similar to that of the compressor. The manufacturer (Lincoln) requires a 30 amp breaker or fuse & 10 gauge wire to the receptacle, BUT comes equipped with a (NEMA 6-50P) 50 amp rated plug but a #10 power cord (it's a molded assembly, by the way). If you remember from my first post, the compressor has the same configuration- a #10/3 power cord with a 50A/250V rated plug (which is where the questions started). Also, I stopped by a local electrical supply house and asked some questions. The guy at the counter informed me that the current draw for a 23.5 amp motor could spike as high as 3x the operating current (75 amps!)at startup, depending on the condition of the motor. He finished the conversation by saying that the 30 amp breaker should be sufficient for the compressor motor circuit(?). So.........., I've ordered a 30 amp double pole GFI breaker, I bought a 50 amp (NEMA 6-50P) receptacle and a single gang weather proof box, and currently have some 10/3 cable lying around. As soon as the breaker comes in, I'll wire it all up, and start plugging stuff in. Luckily, the cable won't need to be buried until I move the equipment to the back of the property. I'll keep an eye on things to make sure nothing is getting hot,but I have a feeling this is the trick.
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As I stated, this saw only requires a 6-15 (2 hots and a ground) which is what is shown in the manual. There's no need for a neutral (nor any place to connect it on that receptacle). In some cases I might run a neutral to the box just in case I needed to hook up a four wire circuit in the future, but here I wouldn't. I have four 240V receptacles in my shop running a larger table saw than this, a dust collector, an air compressor, and a jointer/planer. None of them needs a neutral. 12/2 would be fine here. There's no place to connect that white wire not he 6-20 receptacle. It is not the case that you connect the grounded (white) and the ground (bare/green) to the same bus. This only can happen at the service disconnect. The suggestion of a new panel indicates this MIGHT not be the service disconnect but rather a sub panel. Further, you can not put a single 15A receptacle on a 20A breaker. There's neither a requirement to shut off the main breaker (if there even is one) nor does shutting off the main breaker reenergize everything in the panel. If you don't know what you need to do to work safely in the panel, you should have an electrician come in to do the work.
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DIY Guy
Original Author
7 years ago
I picked up 10g wiring and a 30amp breaker. But I didn't read this info till just now. Multiple forums I read through mentioned using a 30 amp breaker for this unit which was why i went with a 30. The wiring from the power line is brand new to our also brand new 200 amp outdoor main panel and meter box. From the main panel there is also brand new underground wiring which runs about 14' to the 100 amp garage panel. The compressor will use about 20' of 10g on a dedicated circuit. The garage lights are 8.5w LED so I hope that helps with possible dimming.
DIY Guy
Original Author
7 years ago
So far no problems running 30 amp and 10/3 (no neutral wire like mentioned). I used the black and red wires and capped the white. The ground is also there on the switch. The biggest problem is trying to bend and route the 10/3 because of its thickness. Out of curiousity, if perhaps the neutral was to be used, would this be considered a split phase 120/240 that uses both voltages?

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