Why are some 230v compressor motors run on 110v? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 05-21-2006, 12:49 AM
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Why are some 230v compressor motors run on 110v?

I'm wiring up the 15 amp US General with the recommended 30 amp breaker.

It does say 208-230 volts on the motor, but its got 2 wire 14 gauge thats not 230 VAC. Looks like black and white are both neutral, so how do you add a ground or go about this?

Under the pressure switch cap it just shows 2 lines going in, 2 going out.
Line -O O- MOTOR (black)
Line -O O- MTR (white)
MDR 21/ ..20A: MDR 21-EA/ ..20A
240VAC 50-60 Hz

Looks like I'm going to be using more energy than necessary. Theres no black(hot), red(hot) and green(ground). Wondering why do they go this route. Maybe its not as hard as I'm thinking, don't worry, if it is I'll have an electrician come do it. Just trying to learn, since I'd like to maybe do some upgrades in the future and know why they don't just go with a 12/2 230v wire to begin with.

I'm using a compatible THQL GE 2 pole, 30 amp breaker with just 30 ft of 10/2 Romex nicely in the corners of the drywall, with black tape on both ends of the white(hot) wire. Main panel standard ratings are 120/240VAC. 3 wire, 1 phase, 125 ampere max. Optional 240VAC, 2 wire, 1 phase,(it says) for this system neutral is not used. 24 pole max, branch breakers 70 amp max with copper. So it looks like I got some room, plus the dryer and other things won't be used while I'm using the compressor.

I'm thinking with this setup the 2 wire 14 gauge should be OK?

I know its hard to see, it says:
Type-CP, FR-P56, HP-SPL, HZ-60, RPM-3450, Volts-208-230, Time-CONT,
ENCL-DP, Form-KHH, Code-C, Insul Class-B, Amb-40*C



One hole left on the right neutral that'll fit the copper ground. The left side are for smaller gauge ground.


Any info is greatly appreciated.

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Old 05-21-2006, 11:36 AM
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If the unit is new you should be OK Danny. The manufacturer has obtained approval using the smaller wire from the pressure switch to the motor... probably rated at a higher temperature and so can carry the current safely.
Your electric stove or dryer for example have large wires feeding them (from your house panel) but most of the wire inside the unit is smaller but rated for the current. Same with the voltage... each wire will carry 110 volts in any case.

Your ground wire should go on one of the screws in the pressure switch... hard to say from the pic but maybe one of the Phillips head ones (there are 2) on the plate of the box I can see on the bottom. Or there appears to be some sort of screw at the upper left. If the pressure switch is mounted to the metal frame of the compressor you could also just drill a hole in the bottom plate and put a nut and bolt to the ground wire. Bottom line is the ground wants to connect to all the metal of the air compressor.

I find it interesting you are using the neutral bar of the panel for the ground. Works I guess.

Your #10 wire for the feed is fine.

You won't be using more energy than necessary. It looks like this motor draws 15 amps at 230 volts. That would be, to make things simple 15x230= 3450 watts (power). This same motor if it was rated at 115 volts would use 30 amps. 30x115=3450 watts. I'm guessing a 2.5 HP motor or so.

In any case the watt meter on your house would read the same consumption (3450) at either voltage and send you the bill.

The idea of going a higher voltage is to save wiring costs. In your case you would go to a larger wire if running at 115 volts. Also the contacts on the pressure switch would have to heavier to handle more current at 115 volts.

Anyway make sure the frame of the compressor is grounded, don't worry about the factory wiring if it is an approved unit. You're good to go. Make sure nothing is going to hit or hurt the feed wire.

Dave
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Old 05-21-2006, 01:15 PM
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Thank you Dave You explained that very well. Starting to make allot more sense. Maybe there is a plus side to the 110v wire after all. Theres only the 2 screws that look like a good ground, its all metal to the tank, so I think that should work.

I'm glad you brought up the part about the neutral bar on the main panel. Was thinking there has to be a better way, I'm maybe a little too concerned on maximum efficiency since I'm going bare bones minimum on air power. What would any of you suggest be a better alternative to ground?


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Old 05-21-2006, 01:55 PM
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If I was just running 220 and ground I'd have attached the ground wire to the metal of the breaker box (panel). Just left no connection at all on the neutral bar. If the power was coming from the house I would also remove the bonding screw (usually brass) that connects the neutral bar in the panel to the metal of the panel. Then all the ground wires would just go to the ground screws of the panel.

The house part the 2 hots would be on a breaker and the ground wire would attach to a ground lug of the house panel.

It's working for you but just might be confusing to others. As long as BRASS screw is still in place from the neutral bar to the panel, effectively grounding the panel box you should be good to go. I can't quite see from the picture but it looks like the screw to the right of where you attached the ground wire to the neutral bar might be the bonding screw. It may not be brass but in your case it should be there. Else your panel box is not grounded.

Make sure that screw goes right to the metal of the panel. This would ensure that the main ground from the supply goes to the metal of the panel also grounding it.

Dave
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Old 05-21-2006, 06:40 PM
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Your motor shows an amperage draw of 15 amps. Regardless of the wire size at the pressure switch, you should supply it with at least 12 gauge wire, preferrably stranded. The ground wire should go to a green screw in the pressure switch housing (hard to see if there is one there in that pic). Ground wires are supposed to go to a separate grounding strip in your panel, or to the can itself, not to the nuetral bar.
You motor can not be changed to run off of 110volts (most small electric motors can be changed), so the wire colors they used should not matter.
Hope this helps, I'm not an electrician, just a pool repair man that does a lot of control systems and motor installs.
Good luck.
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Old 05-21-2006, 07:03 PM
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Thanks again Dave I'm being as careful as I can taking my time on this. From hearing mixed reviews and what direction to go on these setups, I had to learn more than what just works and gets bye. Also for future safety concerns. And I like the fact that you guys care about those sort of things and would like full performance on your more efficient machines.

I have one last idea, instead of grounding the Romex copper ground onto one of those 2 screws like here in the pic. I found a good sized hole on the back wall of the tank that supports everything on top. Thought of sanding around the hole that can fit a good 3/8 sized bolt in there. And use that as ground going straight to the tank itself. Seems more reliable that way too.

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Old 05-21-2006, 07:35 PM
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Quote:
Originally Posted by Kruzin Karl
Your motor shows an amperage draw of 15 amps. Regardless of the wire size at the pressure switch, you should supply it with at least 12 gauge wire, preferrably stranded. The ground wire should go to a green screw in the pressure switch housing (hard to see if there is one there in that pic). Ground wires are supposed to go to a separate grounding strip in your panel, or to the can itself, not to the nuetral bar.
You motor can not be changed to run off of 110volts (most small electric motors can be changed), so the wire colors they used should not matter.
Hope this helps, I'm not an electrician, just a pool repair man that does a lot of control systems and motor installs.
Good luck.
Thanks for the input. This setup is different and was first expecting what you were mentioning on the green screw. The not so helpful manual it came with showed those setups, but not this one. Only has a total of 4 screws, 2 in, 2 out, and those 2 bottom screws on the plate that appear to be ground.

I'm usiing a good 10 guage from the panel to the pressure swich, white (hot), black(hot), copper(ground). And seeing some folks out there with this unusual setup, and the 2 wire 14 gauge going to motor with the black and white being nuetral, it seems that you have to make your own ground with this setup. Unlike the 230vac 12/2 3 wire to the motor with the BLACK-110, RED-110, GREEN-ground. Thats why I wanted to ask about why some 230V motors are wired to run on 110v.

It appears to work and maybe acceptable soley for the fact that its a more economical thing to do for the manufactures than it seems to help the consumers much. Knowing its a cheap compressor I don't expect the quality to be like the other more efficient ones. But its interesing to see some of these companies doing it and wanting to learn about compressors too that got me interested in the question. Makes me wonder if many other compressors like Coleman,ABAC,and other single stages like Kobalt have there 230v's setup too with the 110 wire to the 230 motor. Looks to work and do the job at least.
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Old 05-22-2006, 01:09 AM
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Quote:
Originally Posted by Danny G.
I'm usiing a good 10 guage from the panel to the pressure swich, white (hot), black(hot), copper(ground). And seeing some folks out there with this unusual setup, and the 2 wire 14 gauge going to motor with the black and white being nuetral, it seems that you have to make your own ground with this setup. Unlike the 230vac 12/2 3 wire to the motor with the BLACK-110, RED-110, GREEN-ground. Thats why I wanted to ask about why some 230V motors are wired to run on 110v.
No the motor is running on 230 volts.

You are running, as you say, a 10 gauge wire from the panel - white (hot), black (hot), copper (ground) to the pressure switch.

The factory is running a 14 gauge wire from the pressure switch - white (hot), black (hot) to the motor.

They are not running a ground wire because once you ground the pressure switch with your copper wire you are in effect grounding the whole compressor (tank and all) because everything is metal. The metal case of the motor is attached to the metal frame of the compressor which the metal body of the pressure switch is also attached. Once you ground the switch you ground everything.

Therefore they don't need the third wire to the motor as it is grounded with the whole machine. It is running on 230 volts.

Dave
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Old 05-22-2006, 03:29 AM
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Dave, you are a great teacher And thanks Kruzin Karl for helping me bring out where some of the confusion was coming from. I guess I am a little too concerned about maximum efficiency, somehow I was thinking the 230v motor would act as a 120v drawing twice the current for the same hp.

Also thinking the 14/2 from the pressure swich wire were also both neutral. And now understanding how the simple grounding works. I was just thinking a little too hard. Thanks again Dave.
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Old 05-22-2006, 01:02 PM
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Danny, I'm an electrician. The reason you have a black & white wire going to the switch from the motor is because that's the way it's made. When they manufacture cable, they don't know what it's going to be used for. It covers abroad field. Since it's #14 AWG, good for 15 amps and your compressor is drawing 15 amps at full load you're OK. This is not a continious duty item, meaning being run for more then 3 hours straight. If it was continious, it would have to be #12 AWG. In addition, it's a very small length and also since the room in the switch is tight, you need the flexability as well. The reason you have a 30 amp breaker is to cover tha amperage draw when the motor first kicks on. This is called starting current. It can be 10X that of the running current, or 150 amps! It's so it won't trip. You're still protected via the short circuit protection of the breaker. When you're dealing with motors, you can have breaker 600% over the rating of the wire in some cases. You're fine in connecting the ground wire of the Romex to the buss bar with the white wire in the main panel ONLY. It it's a sub panel, you'll need it to go to the shell of the panel. BTW, you can strip the wires a little more in the panel, you don't need them that short.
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Old 05-22-2006, 03:34 PM
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Thanks so much for the explanation. I surely know now this compressor will suit my needs for the time being. I've heard some recomendations if the 30 amp breaker trips often on the initial startup drawing like you said up to 6 times the regular load on some machines. Might give the 40 amp breaker a try. Just for less chances of tripping the breaker. Was at first worried the 40 amp would cause too much power draw beyond 15 amps at regular load at first. Now knowing from your great explanation, I have less worries and know what to do if starts to act that way. I just want a little overboard protection for everthing

I will free up some more wire too at the box, just showing an example before I do anything silly. I knew I could get the right answers here from folks like you.
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Old 05-22-2006, 07:37 PM
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Works GREAT

I just want to say thanks again everyone, it just started up for the very first try. I broke it in for a good 20 minutes with the valves open and it sounds great. Turned it off and on a few times and no problems at all.

You can see the initial surge of energy going to motor. Not as loud as I was expecting with the rubber isolators I put on them. But still loud. It would definately eat away at the concrete without them. After 20 minutes the wires were still cold. And at 20 psi I realized teflon doesn't work. lol

Time to get some Rector Seal No.5. All I'm waiting for now is the hydro hose from Northern, and I'm set! You guys rock
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