Compressor question: 240v to 120v

[Bruce Page]

Doug, I'm just curious, has that motor ever driven the compressor pump?

[Doug W Swanson]

Doug, I'm just curious, has that motor ever driven the compressor pump?

Yes. I think the motor was installed whenever the compressor was installed at the station. I made sure I tested it out and ran it for a short period before I put a bid in on it .

[Art Mann]

I agree that 120VAC, 15A power will most likely work well. There is one warning I will toss out. If you are running multiple machines off that off one circuit (breaker), you may occasionally trip the breaker if the compressor cycles on while you are also using some other power tool. I have that situation but I don't leave the compressor on unless I am using it a lot.

[Doug W Swanson]

Should run on 120V fine. Open the junction box on the side of the motor (on the far right of your picture), and there should be 6 wires (labeled "T1" through "T6"), plus two supply wires coming in. Reconnect the wires as illustrated in the picture (T1, T3, T8, and one supply wire connected together, and T2, T5, T4, and the other supply wire connected together).

Currently the pressure switch has two black wires and a ground going to it. Then two black wires run to the motor. I've got the motor wired as Line/T1/T3/T8 and Line/T2/T4/T5 as the diagram shows. Am I right in thinking that I need 120v running to both of those wire bundles? Or is just one OK? Do I need a neutral? If so, where would it go?

I've looked online and really can't find a good wiring diagram of what I'm trying to do so that's why I need a little help. I've done plenty of wiring on my house but it's either been 120v or 240v. I haven't had to go from one to the other....

[Bill Dufour]

For 120 you need one hot lead and one neutral. Not sure how that relates to the internal motor windings but only two wires and ground will come out of the motor wiring box and into the supply line.
Normally neutral is white but in your case you will use one of the black leads as neutral. You should mark it white at both ends with tape, whiteout or paint. I would leave the pressure switch as is and switch both neutral and hot at the same time. You do not normally switch the neutral wire but in your case it is already done and it would be a waste of time to jump around the switch for neutral.
Bill D.

[John K Jordan]

... and it would be a waste of time to jump around the switch for neutral.

And especially if someone switches it back to 240 some day!

BTW, Doug, I suspect the switch on the side is not so much a pressure relief but simply a switch to turn the motor on when the pressure gets low and off when the pressure is high enough. Some have a knob or screw for adjustment. A pressure relief is often a mechanical spring-loaded pop-off valve that releases pressure in the tank in the event the compressor fails to cut off or maybe if the tank gets too hot. At least that's the way it works on the four compressors I have.

JKJ

[Doug W Swanson]

And especially if someone switches it back to 240 some day!

BTW, Doug, I suspect the switch on the side is not so much a pressure relief but simply a switch to turn the motor on when the pressure gets low and off when the pressure is high enough. Some have a knob or screw for adjustment. A pressure relief is often a mechanical spring-loaded pop-off valve that releases pressure in the tank in the event the compressor fails to cut off or maybe if the tank gets too hot. At least that's the way it works on the four compressors I have.

JKJ

Yes, you're right, John. I've been calling the pressure switch the wrong thing. Fortunately everyone here knows what I'm talking about

[Doug W Swanson]

IMG_1002.jpg

I've got the motor rewired as per the diagram and here's the pressure switch. The two outside terminals are labeled 'line' with the two black wires coming from power while the two inside terminals are labeled 'motor'. So what I'm hearing is that I change one of the two black 'line' wires to a neutral and everything would be ok?

I think what I may do is just buy a new power cord and replace the flex conduit that is currently there.

[Thomas Canfield]

I don't think I saw it, but to change from 220 to 110 you need to make 2 changes. The plug on line to the pressure switch will need to be changed for 110 service. Then you will need to change the L1 and L2 connections and other terminal connections in the motor housing. It was mentioned that the 14 amp at 110V may present a problem if it is not a dedicated circuit and there are other users on the circuit (shop vac, drill, etc) and cause frequent tripping of breaker. I just bought a new air compressor and changed it to 220V to keep from overloading the standard shared 110V circuits. The 220V circuit used is shared but all loads are only 15 amp, well under the 20 amp breaker.

[CPeter James]

If this was in a fire station, it was most probably used to maintain the air pressure in the fire truck air brakes so that when the trucks have to respond to a fire, they don't have to wait for the air pressure to build up. For this purpose, they would not need a high volumn pump and the 1 hp motor would have been sufficient. Being a government installation, I would suspect that it is a high quality USA made compressor and worth putting a little money into it to get it going.
CPeter

[Doug W Swanson]

Went to Menard's this morning and bought the necessary supplies and got the compressor fired up this afternoon. Everything works great!

Thanks for all of the advice!