Need Help Wiring old Air Compressor

I have an old Craftsman Twin Cylinder air compressor that has no
plug/cord wired in at the moment. I need to learn the correct wiring
procedure in order to connect this 230V motor to my existing 50amp 250V
plug in my garage. The house was built in the 60's and all the wiring
is original. Therefore, I have provided pictures of each component in
question, sorry you have to cut and paste.
First here are pictures of the existing 50amp 250V Plug in my garage.
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Second are pictures of the compressor and its' motor face plate,
wiring, and wiring diagram.
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Third is a picture of the wiring block on the compressor.
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My intentions are to purchase a NEMA 10-50P and 10ft of 12-3 power Cord
and simply wire the Red and Black wire to the two terminals on the
wiring block. Leaving the white wire disconnected. Is this the proper
thing to do or am I going to cause some sort of electrical hazard? The
red and black are my two hot wires right? By the way where is a good
place to look for the 10-50P, I have tried my local Home Depot and
Lowes but they don't carry them. Any help would be greatly appreciated.
Thomas
Reply to
T-Man16
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This might be better over at alt.home.repair .... but anyway.... I would install a disconnect box somewhere near that appliance outlet and run a flexible conduit with all the proper fittings to your compressor. I can't tell how far the outlet is from the compressor...It should be pretty close. Just go to the hardware store and they should be able to help you. If you don't fell comfortable with all this you might just hire an electrician to do this for you. Please do not use that outlet...the rusty screws are not safe.....Ross
Reply to
Ross Mac
Thanks Ross..I will post on the other group as well. The outlet is right above the compressor just didn't put it in the shot. I can replace the screws or just switch out the outlet box for something more suitable to my situation. I just felt uncomfortable becasue I wasn't sure of the wiring to the motor and that is why I placed the topic here.
Thomas
Reply to
T-Man16
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Wow someone who posts a question with the information provided.
First you realize that the 50 amps is WAY over the 15 amp draw of the compressor? Not code to connect directly. Your going to need to either fuse down the wiring in the panel, new 20 2 pole breaker or your going to have to remove the plug you have install a fused disconnect and use that for the protection of the motor. I prefer fuses for motors, just a simple pull out disconnect would do. A manual motor starter would be better.
The pressure switch needs one of the lines brought to and through it. then to the motor. The other hot just lands on terminal 2. This way the pressure switch controls the on and off. You did not show the other end of the cord on the pressure switch so,,,, no joy there.
I would use #12 stranded wire and "push-on terminals" some would use ring terminals inside the motor. Your compressor your choice. The ground wire would land under the cover screw or ground screw if available. 12-3 SO cord would be a good choice, SJ if you want to save a tad of cash.
Have fun, hope I helped not hindered.
Reply to
SQLit
SQ left you some great additional info and I wanted to add....good post with lots of information....Ross
Reply to
Ross Mac
SQLit, Thanks for the info, I have a few clarifications.
The motor is thermally protected and has a red button to reset the motor when it has a problem. Do I still need this additional protection...is this internal circuit breaker not safe enough? I realize 50 amps is too big...I was just trying to simply use the outlet because it was already there. I felt it would be easy to find a plug that fits the outlet and run a short cord to the pressure switch. This compressor will not be left plugged in and will only be used when I am actively working on a project. Although, adding a fused disconnect sounds easy and I could then go with a 20 amp 240V outlet with matching plug..right?
The first image is of the pressure switch with the cord attached that is coming from the motor and the second image is of the same cord but the other end which is attached to the motor at positions 2 and 4 using push-on terminals. The wires are simply black and white and you will notice that there is an empty hole next to the cord going into the pressure switch this is where the original plug cord was but is now missing.
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what you are telling me is that when I use lets say 12-3 SO cord that the red and black should go to the two screw terminals labeled line that are directly across from the white and black wires and then the white(neutral/ground) wire should be attached to the cover screw at the pressure switch...right?
Thanks for you assistance Thomas
Reply to
Thomas & Paige
You need a ground, which you don't have at present. And the 50 amp is oversized for the motor and connecting wiring, regardless of the motor's thermal protection.
...is this
Yes.
Red----Pressureswitch-----motor terminal 2
Black---------------------motor terminal 4
Ground--------------------motor frame
Re-identify the white as ground by wrapping it with green tape, at both the service panel and the outlet ends. Replace the existing receptacle with one rated for 20A, 230 V. Wire the motor with SJ to a mating 20 amp plug. At the motor, connect the ground wire to the metal frame of the motor. Replace the 50 amp breaker at the panel with a 20 amp breaker. Alternatively, instal the 20 amp disconnect between the 50 amp branch circuit and the 20A receptacle for the motor. In either case, re-identify the white wire as ground and ground the motor frame.
Ed
Reply to
ehsjr
Ed,
Thank you for the information. I will utilize a 20amp fused disconnect and go with 20amp 240V outlet and plug using 12-3 wire. I will attach the black and red to the line side at the pressure switch and the white I will attach to the clip/screw that holds the cover to the pressure switch. I confirmed continuity between the motor chasis and the clip at the pressure switch so they are common.
My confusion was that I did not know that 240V circuits did not need a neutral for the return path of electrons but rather the hot leads traded off acting as one. I kept asking my self how/where to attach the white wire because it was obvious at the pressure switch that there were only two terminals and both had to be hot in order to get the 240V. Now I can safely wire up the compressor and know what is going on. Do you think the original cord would have grounded the white wire in this manner? A consumer in the 70's would not have known that the white was acting as a safety ground (green) rather than a neutral.
Thomas
Reply to
T-Man16
I would guess that it is exactly as you surmised - the neutral (white) was used as ground. Your description of how you'll wire it sounds good.
Ed
Reply to
ehsjr

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