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240 volt 4 prong

1913 Views 16 Replies 6 Participants Last post by  Eaglespoolin
I have a 240 volt air compressor with a 3/4hp 3phase motor on it. My questions are can I put a 4 prong plug on the compressor and use that outlet? The compressor has 4 wire comming out with no plug is how I bought it. Or do I have to use 3 prong 240 without the 120 line. I'm going to be using a phase converter to use residential power. Only reason I bought a 3 phase is because I got a deal of a lifetime on it and could not pass on it. I'm not asking to wire up a new receptical just needing to know if I use 4 or 3 prong because I have a 4 prong outlet already hooked up I'm just going to make a 240 exstention cord to run off that untill I run a whole new line for perm install thanks for the help!
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You'll need nema 15-xx for the receptacle and plug. The xx is the amperage. The 15 denotes a 3 phase 250 volt circuit. Don't use a nema 14-xx as that is for single phase four wire circuits.
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So I have to add a new 240 from my box in order to run that compressor even with a phase converter? If the compressor has four wires comming out that means its a 15-xx. Im running a phase converter am I able to just use the receptical that's already ran? It's four wire was for my dryer in house. Or are you telling me I need that 15-xx to make the run from outlet to compressor. I'm sorry I know nothing about high voltage 3 phase sorry if I sound confusing and making no sense. Thanks for responding!
You cannot run a three phase motor off
A single phase 240v line without a phase convertor
It may be easier to change the motor.
You're confusing me. Did you purchase the compressor and Phase converter as a unit together?? I assume the converter is of the appropriate voltage for compressor. (there are different 3 phase system voltages) Be sure the converter output voltage matches the needs of the motor on the compressor.

I assume you need a certain voltage to that converter. What does it need 120V, or 240V to operate. Once that is determined feed the converter with the appropriate voltage and amperage (circuit) for it and the compressor to operate.
Then you mention a 4 prong plug for the compressor and use that outlet. WHAT OUTLET? Is there an outlet on the phase converter to plug the compressor into? If that is the case the outlet should have a NEMA number imprinted on the front indicating amperage / voltage and NEMA configuration 15-xx or possibly L15-xx (the "L" indicating it's a twistlock receptacle). Once you install the appropriate plug put into the receptacle, energize the circuit and turn on the compressor. BE AWARE that the motor could possibly run backwards. If this happens shut everything off, remove the plug from the receptacle and change any TWO of the THREE power leads to a different terminal on the plug. Put it back together and try it again. It should be running in the correct direction now.

I stress though be sure the Voltage on the converter matches the Voltage on that motor.

You may want to hire an electrician to take a look at it. I mean if you saved that much money purchasing it, there must be something in the kitty to have it hooked up properly.

I did not comment on the phrase "Or do I have to use 3 prong 240 Volt without the 120 line." I have no idea what that is supposed to be referring to.
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The motor needs four wires, three hot phases and ground.
Sorry for the confusion the compressor motor says 208-230/460 I bought the generator with out a phase converter the compressor was used in a school to operate some type of valving. I'm going to order a phase converter to convert the 1phase 240 into 3 I do know I will only have 2/3 of the rated horsepower going this rout. I seen converters online for about 60 bucks for a 1/4 up to 1hp motor. The motor on the generator is 3/4hp. I rather try to convert my power to use a converter instead of buying a new motor just because that will run me more than I payed for the thing but if I have to I have to. The plug I was asking about using to run from and to the converter is the 4 wire 240 outlet in my house I was asking if I can make an extention cord and run it outside roughly 10ft instead of wiring a new run from breaker

What I was saying about the 3 wire I was asking if I needed to use a 3 wire or 4 wire circuit to run this compressor I assume 4 since there is 4 wires coming out from the precious hookup.
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Here are picture of the outlet I want to use and motor specs.


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As I believe has already been mentioned but not by me, in looking and thinking about this being you haven't purchased a phase converter YET, I would get rid of the 3 phase motor and get a single phase. You'll be a WHOLE lot happier. The motor will operate at specification not at 2/3 of what it should be operating at. All you're doing with the current situation is asking for motor problems down the road. JMHO
Any motor (single or 3 phase) that has a 56 frame and is 1725 RPM (or thereabouts) will fit with no modification.

There are tons of 3/4HP 56 frame 1725RPM single phase motors on eBay and other sites.

How does the pressure switch control the motor? If using a phase converter, the converter needs to be running ignorer to start the motor. The switch cannot control the single phase power to the converter.

How is the 3 phase motor protected against overload, single phasing and failure to start? The motor shown in the pic does not have any built-in overload, it'll need to be provided separately.

In my opinion, replacing the existing motor with a single phase one would be the best solution.

Thanks I understand I have not gotten the converter yet wanted to learn about this setup before doing anything I will look into a single phase motor.
Now do I go with a single phase 240 or a 120 what would be best?
240 Volt. That's the best option for you.

Is there a motor shop in your vicinity? If so ask them if they'd be interested in your motor. Something is better then nothing even though you could try selling it yourself.
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What is this setup worth I have no idea I'm trying to trade for single phase or sell it if anyone wants it on here.


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