Air Compressor wiring issue. I'm stumped

[Methodical]

I just received my new compressor - Maxair 5hp, 18.5 cfms @100, load of 22.5 amps - calculated ampacity is 28 amps (see link below). I wired the unit just as stated on the pressure switch; black hot line to opposite lug from the black motor wire and white hot line to the opposite lug from the white motor wire and ground, however, it constantly trips the breaker and never starts. Here’s my wiring set up; 40 amp circuit (8/3 awg wire - neutral not wired to compressor) from main panel to sub panel in garage, 30 amp breaker in sub panel (also tried 40 amp) and 10/2 wire from sub panel to compressor. I have 240v at sub panel and on the 10/2 cables feeding the compressor, however, as soon as I connect the cable to the pressure switch the circuit trips. I have not connected the cable directly to the motor yet to see if that gets it started, but plan to do it when I get home (just too tired last night). I’m stumped and need a sanity check. The wiring is not rocket science, but something’s definitely wrong.

1. Has anyone here experienced this with a brand new unit?
2. What else should I test?
3. Will the motor continue to run if I connect directly to the supply? Curious.
4. What does this statement mean? “line to ungrounded side of supply-when grounded supply is available” This is stated on side of the motor.

Air Compressor


Thanks for any help or insight…Al

 

[2xs]

The way you are describing the wiring doesn't make sense at all. The two incoming leads from your panel need to go on the pressure switch on line terminals. The compressor wires should be hooked to the load side of the pressure switch. If this is way you have it connected then it should be correct. My suggestion is to take the guard off and attempt to roll the compressor by hand with or without the belts on and see what happens. It is possible the compressor is seized you may have bad capicators on the motor. If you can roll the compressor by hand take the belts off and attempt start the motor without a load on it. If it starts fine double check the capicators and then start check out the compressor it's self. Hope that helps. Yeah I think your pressure switch is wired wrong or is junk. The motor will run if connected directly to the power source. Follow the steps I laid out with the power off and if can't get it going don't get too crazy and pay an electrician for there expertise so don't kill yourself or burn down your house.

 

[justsam]

What you describe sounds like you have wired it all correctly, double check markings. Make sure that you have the black and white line power going to both lugs that are marked LINE. If you have one on the LINE side and the other on the LOAD side, you have created a direct short when switch is closed. If this all checks out then proceed...

I would remove power and remove the line feeding the pressure switch. Measure resistance from each of the terminals, black and white to ground and also between each other. there should be some high resistance, certainly no short. If good there, I would lift motor leads and do the same thing.

I assume the pressure switch is in the closed position, so black should be connected to black and white connected to white. It is a Double Pole, Single Throw switch in essence.

Certainly your notion of wiring the motor directly should also validate where your short may be.

 

[Methodical]

The way you are describing the wiring doesn't make sense at all. The two incoming leads from your panel need to go on the pressure switch on line terminals. The compressor wires should be hooked to the load side of the pressure switch. If this is way you have it connected then it should be correct. My suggestion is to take the guard off and attempt to roll the compressor by hand with or without the belts on and see what happens. It is possible the compressor is seized you may have bad capicators on the motor. If you can roll the compressor by hand take the belts off and attempt start the motor without a load on it. If it starts fine double check the capicators and then start check out the compressor it's self. Hope that helps. Yeah I think your pressure switch is wired wrong or is junk. The motor will run if connected directly to the power source. Follow the steps I laid out with the power off and if can't get it going don't get too crazy and pay an electrician for there expertise so don't kill yourself or burn down your house.

Maybe my way of describing it is confusing, but the power lead coming from the subpanel is connected to the line side of the pressure switch - black to black and white to white. I will try turning the compressor by hand before I connect directly to the motor. Btw, the company stated that they ran the compressor before shipping it, which I believe because it had a little air in it that I drained, so between them running it and me getting it, it seems like something went wrong.

Oh and you mentioned that the motor may have seized. I know things can happen, but this is a brand new compressor.

Thanks for the input.

What you describe sounds like you have wired it all correctly, double check markings. Make sure that you have the black and white line power going to both lugs that are marked LINE. If you have one on the LINE side and the other on the LOAD side, you have created a direct short when switch is closed. If this all checks out then proceed...

I would remove power and remove the line feeding the pressure switch. Measure resistance from each of the terminals, black and white to ground and also between each other. there should be some high resistance, certainly no short. If good there, I would lift motor leads and do the same thing.

I assume the pressure switch is in the closed position, so black should be connected to black and white connected to white. It is a Double Pole, Single Throw switch in essence.

Certainly your notion of wiring the motor directly should also validate where your short may be.

I'm positive all the wires were connected correctly. I think it's the pressure switched. I will test resistance and see what I get.

Thanks for the input.

Btw, would it be ok to use stranded 10/2 wire? I ask because it's a bare working with solid wire in such a small space.

Thanks...Al

 

[nehog]

(really, someone may spot something you missed!)

 

[JakeKohl]

stranded vs. solid shouldn't make much difference from a power standpoint. However, you should have stranded wire going to the compressor because of the regular vibration the wire will need to be able to withstand.

I would NOT recommend connecting directly to the motor. The switch/relay is a very simple device. If you have something wrong with your power, you could fry the motor (or worse, energize the entire compressor and get shocked). You should be able to troubleshoot the problem you have with a multimeter and what is currently in front of you.

 

[Davefr]

At this point I'd remove the belt and wire directly from circuit breaker to motor leads. (bypassing pressure switch). If the motor runs fine then move the power leads to the line on the pressure switch and see if the motor starts with tank PSI < cut in PSI.

For these simple tests you can use 10/2.

If the above tests are OK then the problem lies within the pump. Does it turn fairly easily by hand?

 

[Methodical]

(really, someone may spot something you missed!)

I am at work now and don't have any. I will try and get some.

stranded vs. solid shouldn't make much difference from a power standpoint. However, you should have stranded wire going to the compressor because of the regular vibration the wire will need to be able to withstand.


I would NOT recommend connecting directly to the motor. The switch/relay is a very simple device. If you have something wrong with your power, you could fry the motor (or worse, energize the entire compressor and get shocked). You should be able to troubleshoot the problem you have with a multimeter and what is currently in front of you.

I think I will get some stranded wire to make wiring a bit easier in that tight box. I will do some more testing to see what I get. I just know if the motor spins with a direct connection that the pressure switch is the only means of going from power box to the motor and must be the culprit. But, I'll do the resistance testing 1st.

At this point I'd remove the belt and wire directly from circuit breaker to motor leads. (bypassing pressure switch). If the motor runs fine then move the power leads to the line on the pressure switch and see if the motor starts with tank PSI < cut in PSI.

For these simple tests you can use 10/2.

If the above tests are OK then the problem lies within the pump. Does it turn fairly easily by hand?

I won't be able to do anything until I get home from work. I will update.

Thanks all for the input and for providing more areas to check.

Al

 

[bochnak]

Is this unit equipped with a magnetic starter?

 

[pattenp]

Once you turn on the power is it an instant trip or is there a little lag before the trip?

 

[Methodical]

Is this unit equipped with a magnetic starter?

Not that I am aware of. It's a direct wire to the pressure switch

Once you turn on the power is it an instant trip or is there a little lag before the trip?

Good question. Yes, it's an instant trip, no lag at all.

 

[pattenp]

If it's an instant trip I'm thinking something with the wiring is connected wrong. If the compressor or motor was seized it would be more of a lag before tripping. In other words it sounds like a trip from a short instead of a trip from an overload. Plus if it was an overload the safety over current protection on the motor would trip.

 

[nehog]

If it's an instant trip I'm thinking something with the wiring is connected wrong. If the compressor or motor was seized it would be more of a lag before tripping. In other words it sounds like a trip from a short instead of a trip from an overload. Plus if it was an overload the safety over current protection on the motor would trip.

If it was wired correctly and the motor was bound up, you'd hear a god awful humm and then after a short while it would trip. That's why I asked for photos, I'm guessing it is wired wrong (perhaps from the factory?)

 

[oltruckag]

I just received my new compressor - Maxair 5hp, 18.5 cfms @100, load of 22.5 amps - calculated ampacity is 28 amps (see link below). I wired the unit just as stated on the pressure switch; black hot line to opposite lug from the black motor wire and white hot line to the opposite lug from the white motor wire and ground, however, it constantly trips the breaker and never starts. ...


Thanks for any help or insight…Al

It might jut be your wording, but it sounds like you've wired a hot to ground... That'll trip it as soon as you flip the breaker.

Typically the pressure switch will have 4 terminals - each pair connects when the switch closes. The motor should wire to the inner screws and the line to the outer. (inner vs outer doesn't really matter, just the way I like to wire 'em)

Tyson

 

[oltruckag]

I went to the site to check the manual - it has this confidence inspiring warning under the Wiring section of the manual:

All wiring information is stated on the electric motor and on the pressure switch or provided with the magnetic starter, if supplied. WII Customer service personnel cannot, by law, provide any wiring information.

Not sure what law they are referring to, but I'll need a pic of the wiring diagram from the installed switch to give better advice...

Tyson

 

[Methodical]

Hello everyone. I just got home and will start the diagnostics and will get some photos, so everyone can see what I'm working with.

One thing I did last night is open the cover of the motor wires and one thing that caught my eye is the black wire from the motor is running to the #2 lug on the pressure switch, but is connected to the #4 tab inside the motor and the white wire runs to the #6 lug on the pressure switch, but is connected to the #1 tab on the motor. I don't know how if that is right or wrong, but I was expecting the them to match. I have photos which will make it easier to see what it is I'm talking about. Something just doesn't seem right. I'll be back shortly.

Thanks for hanging in there with me.

Al

 

[Davefr]

Hello everyone. I just got home and will start the diagnostics and will get some photos, so everyone can see what I'm working with.

One thing I did last night is open the cover of the motor wires and one thing that caught my eye is the black wire from the motor is running to the #2 lug on the pressure switch, but is connected to the #4 tab inside the motor and the white wire runs to the #6 lug on the pressure switch, but is connected to the #1 tab on the motor. I don't know how if that is right or wrong, but I was expecting the them to match. I have photos which will make it easier to see what it is I'm talking about. Something just doesn't seem right. I'll be back shortly.

Thanks for hanging in there with me.

Al

There might not be any correlation between the numbering on the pressure switch and numbering on the motor.

You need to focus on just the motor at this point. Confirm the motor's two "line" connections and connect them to the breaker. Flip the breaker to on and see if the motor starts.

If the motor doesn't start or trips the breaker then all your focus needs to be on the motor as the culprit. However I'd contact the manufacturer if it's a new unit. You could void the warranty if you start opening up the motor.

 

[pstnbly]

My advice would be don't dig any deeper, put the motor cover back and don't change anything in there. 2nd Occams razor, the simple answer is probably right, meaning the pressure switch was wired improperly in the field (your wiring). The instantaneous trip (as has been said) tells that tale. There are 2 sets of contacts on the pressure switch. 1motor wire and 1 line wire go to each one, look carefully at the switch contacts to confirm, then move forward.

 

[JakeKohl]

My advice would be don't dig any deeper, put the motor cover back and don't change anything in there. 2nd Occams razor, the simple answer is probably right, meaning the pressure switch was wired improperly in the field (your wiring). The instantaneous trip (as has been said) tells that tale. There are 2 sets of contacts on the pressure switch. 1motor wire and 1 line wire go to each one, look carefully at the switch contacts to confirm, then move forward.

^spoken like a man who has fried things by digging too deeply^ (like me). I really wouldn't wire that motor directly.

 

[larry_g]

Check your voltages. Confirm that you have 240V across the black and white wire you are connecting to the pressure switch. Confirm that the motor wiring is also configured for 240v. I'm making an assumption that your motor is not 120/240v but it might be. For a 240v supply you should be using red and black, not red and white as white is usually common, so I wonder if you are supplying 240. Does the breaker that trips have two handles connected and the white wire leaving the panel connect to a breaker?

lg
no neat sig line

 

[MN4x4]

AS stated above, pictures would be a HUGE help in order for us to help you. It's hard enough to do with a good image, and even harder just going by words.

Take good pictures of the pressure switch, as well as the on-off switch. Post 'em when you can.

 

[Methodical]

I went to the site to check the manual - it has this confidence inspiring warning under the Wiring section of the manual:

All wiring information is stated on the electric motor and on the pressure switch or provided with the magnetic starter, if supplied. WII Customer service personnel cannot, by law, provide any wiring information.

Not sure what law they are referring to, but I'll need a pic of the wiring diagram from the installed switch to give better advice...

Tyson

Tyson, I don't know which law they are referring to either, however, they were very helpful when I called them. They asked if I were a licensed electrician and I told them not by trade, but that I was an Exterior Power Lineman (Pole Jock) in the military, so they eased up on that statement. I think the language is there to protect the warranty and their backside.

Update everyone. I apologize for the late response - between work, family and just being flat out tired, I just took a step back for a minute to rest my mind since I had not gotten much sleep the day before.

I did some diagnostics - tested continuity between the pressure switch line and motor terminals and found that there was continuity, so ok there. Also, spun the compressor by hand with ease to ensure it was not stuck. So, I then decided to get some 10 awg stranded wire (to replace the 10 awg solid wire) and some spade connectors. I reconnected everything just I did before (black to black, white to white and ground) and turned on the breakers and when I saw that they did not trip, I knew I was good, so I flipped the compressor switch and she fired right up . So, what I figure is that the solid wire, for whatever reason, was not getting full contact inside the terminals of the pressure switch - maybe they lost full connection when I had to bend the solid wire to allow room to replace the pressure switch cover. As stated before, there is very little room to connect and maneuver any wires inside the pressure, let alone 10 awg solid wires.

Thanks everyone for chiming in. I very much appreciate you taking time to help me.

Al

Btw, I've included a few shots of my setup. Note: those stickers on the compressor has got to go.

 

[pattenp]

Suggestion... wrap some red tape on the ends of the white to identify it as a hot.

 

[plow]

Check the black wire on the top right of the pressure sw. It looks thin to me. The rest looks ok.

 

[Methodical]

Suggestion... wrap some red tape on the ends of the white to identify it as a hot.

Check the black wire on the top right of the pressure sw. It looks thin to me. The rest looks ok.

Will do. Plow, I'm not sure what size wire the manufacturer used on the right side, but I think it's 10 awg wire. Thanks for the suggestions.

Al

 

[JakeKohl]

... Note: those stickers on the compressor has got to go.

You are not kidding. Those decals are really gaudy! They would be sufficient while advertised in a store for a "hey, look at me!", but it's too much for a shop.

 

[fnieto]

Nice job,
Although I don't care for those decals, Its your equipment. The yellow base paint would look cool with some Black stripes or Hot rod decals instead.
On a more serious note, If you plan on running your compressor a lot, a mag switch would benefit you in the long run.

 

[Methodical]

Nice job,
Although I don't care for those decals, Its your equipment. The yellow base paint would look cool with some Black stripes or Hot rod decals instead.
On a more serious note, If you plan on running your compressor a lot, a mag switch would benefit you in the long run.

Thanks and can you elaborate about the magnetic switch - benefits/drawbacks of having/not having a magnetic starter in an air compressor? Also, which do you recommend?

Thanks...Al

 

[fnieto]

Methodical,
A magnetic starter protects your motor from high amp spikes at start up.
It does look from your photos, your using a Condor overload relay. Thats a good thing.
Many single phase compressors come only with a pressure switch which end up "welding" closed the contacts resulting in a continuos run situation. Your pressure switch is definitely a better control set up. Leave it alone and run your compressor. If and when the time comes for a replacement then consider a mag start switch.

 

[pattenp]

On your size motor I wouldn't worry with a magnetic switch. The main benefit you'd get is that the compressor would not restart on its own after a power failure. The magnetic switch disconnects on a power failure whereas your current switch will stay on and the compressor would start up on power being restored. The magnetic switch also provides overload protection, but your motor should already have built in overload protection.

 

[Trey T]

I believe those are the higher-end Condor pressure switch with thermal overload; check again. If it's that the case, you don't need a "magnetic starter" like everyone else mentioned.

Thermal overload put your system in check to ensure you don't overheat your equipment (or duty cycle) and the contactor/switch. That feature is the exact feature as in the "magnetic starter"

 

[Charles (in GA)]

Magnetic motor starters serve two purposes. 1) to act as a thermal overload for the motor. Starters that have thermal overloads built into them will have the overload overheat when the motor draws too much current, simulating the motor getting too hot, and the overload will trip, shutting down the motor.

In the case of the OP, he has a motor with a built in thermal overload, the red button near the top of the end frame, so the thermal overload of the motor starter is not needed.

2) other reason for the magnetic starter is to keep from burning up pressure switches (on compressors, and to keep from using huge manual switches to operate the motor on other devices). Few pressure switches are designed to handle 30 amps or close to it for any length of time or very many on/off cycles. The contacts will burn up. Pressure switches large enough to really handle the current successfully for a long time, are expensive and found in industrial settings. The workaround is to use a rather small, light weight pressure switch, and a magnetic starter. The pressure switch controls the coil of the magnetic starter, a very low amp draw, and the magnetic starter, which has very large contacts in it, does the make and break of the full current going to the motor. You are simply saving those marginal pressure switches from frequent and inconvenient failure.

Charles

 

[plow]

Will do. Plow, I'm not sure what size wire the manufacturer used on the right side, but I think it's 10 awg wire. Thanks for the suggestions.

Al

Sorry, I should have made myself more clear. The wire I'm talking about looks like it may have a problem at the point where the terminal is crimped to the wire. IE, under the heat shrink. It may be the pic tho.

 

[theoldwizard1]

Suggestion... wrap some red tape on the ends of the white to identify it as a hot.

Boy, am I glad you said that !

 

[MN4x4]

That's a fairly simple wiring setup. If you check with a meter do you have 240 VAC at the left side of the pressure switch (line) and also at the right side (load)?

Edit: Sorry - just looked at the pictures and didn't read the text. I see that you got it working, so good for you!

 

[Rickedstyles]

Atleast people in the next county will know what the cfm rating is!

 

[Norcal]

Suggestion... wrap some red tape on the ends of the white to identify it as a hot.

Boy, am I glad you said that !

It is a code violation to do so, cannot reidentify a white conductor in a conduit, only can do so when it is part of a cable assembly, needs to be changed to a color other then white, green, or gray.

 

[theoldwizard1]

It is a code violation to do so, cannot reidentify a white conductor in a conduit, ...

Well if the OP is running individual conductors that makes perfect sense. I guess I was assuming he had NM inside the flexible conduit.

Still, for amateurs, a bit of red tape would help.

 

[Methodical]

Hey thanks everyone for explaining the magnetic starter. I will definitely keep than in the back of my mind if I have an issue in the future.

Plow, I kinda figured that's what you were talking about. I thought the same thing when I first saw the wire. It seems they left a little extra wire (then put heat shrink on it) so they could shape the wire to fit inside the pressure switch housing because it's really tight in there. I don't know why they don't provide a little more room to work with.

Btw, I began removing those stickers - haha!

 

[Trey T]

I have a used magnetic starter rated 5hp 1ph and pressure switch for straight trade for your Condor. Let me know.