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Tool Talk Discussion Forum

Compressor electrical question

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Stephen Newell

01-04-2013 11:05:33




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I keep burning up pressure switches on my compressor. 5 hp single phase 220. It was recommended that I use a magnetic switch to keep from doing that. Should the power run through the magnetic switch, then the pressure switch to the motor or through the pressure switch, magnetic switch then the motor.




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Stephen Newell

01-05-2013 08:59:22




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 Re: Compressor electrical question in reply to Stephen Newell, 01-04-2013 11:05:33  

This is where I am now. Is is anywhere near what was intended for the switch. A1 and A2 are each side of the coil.



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George Marsh

01-05-2013 14:33:51




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 Re: Compressor electrical question in reply to Stephen Newell, 01-05-2013 08:59:22  
Stephen, Don't think this will work. There are no shorts, it just won't work. Going to throw down a challenge to all the experts to post a pic of their wiring diagram first. After all else fails and the experts have given up, I'll post a pic of how to wire to safely, providing all parts of your contactor are good.
George



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Stephen Newell

01-05-2013 16:09:24




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 Re: Compressor electrical question in reply to George Marsh, 01-05-2013 14:33:51  
Could you explain what you mean by being no shorts?



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George Marsh

01-05-2013 18:48:46




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 Re: Compressor electrical question in reply to Stephen Newell, 01-05-2013 16:09:24  
Stephen, The defination of a short is when you wire something sending power to ground. Your circuit wouldn't work because you had A1 going to terminal 98, which is a normally open switch. A1 would have never seen power from the pressure switch.

You shouldn't have any problems with DH's diagram. Perhaps the only problem you are going to get is from the code people telling you it shouldn't be done that way. Wait and see.
George

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buickanddeere

01-07-2013 05:37:37




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 Re: Compressor electrical question in reply to George Marsh, 01-05-2013 18:48:46  
Quoting Removed, click Modern View to see

The definition of a short circuit is not limited to just a connection to ground.



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Stephen Newell

01-06-2013 06:01:03




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 Re: Compressor electrical question in reply to George Marsh, 01-05-2013 18:48:46  
I see that now. I thought over the course of working on this thing I had probed it every which way with an ohm meter. There is nothing between 97 and 98.

I think the code people have moved on. I don't see a problem interrupting L2 at the pressure switch also if that is what you mean. Anyway this is Texas and just about any electrical work goes here. I recently remodeled a house where the homeowner hired an electrician to run a wire for a new kitchen stove some years before. While I was there one leg of the wire went dead and they had me look at it. I found the guy had pulled an aluminum wire tighter than a banjo string through the attic and down in the wall and wired it without a breaker directly to the electric meter. Then someone later on had the bright idea of using wood shavings for insulation in the attic and the wire was buried in it.

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DH in Carolina

01-05-2013 15:41:45




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 Re: Compressor electrical question in reply to George Marsh, 01-05-2013 14:33:51  

Here's the simple way to wire the contactor. you can't use the overload block because it is for three phase and you only have single phase power. Solid state overload must see current on all three legs or it will trip out. This will work if you have internal motor overload protection. If you don't have motor protection get a single phase conbination starter with overload protection. If you ever worked on industrial equipment you will find most motors don't have internal overload protection.

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Stephen Newell

01-05-2013 16:41:28




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 Re: Compressor electrical question in reply to DH in Carolina, 01-05-2013 15:41:45  
Thankyou for the sketch. I now finally have given up on the overload protection and have taken it off for good. Overload protection is shown in the owners manual and also in different sketches I found online. Not having a complete understanding of this magnetic switch I kept fealing like if it was there it was suppose to be there. The motor that I have on the compressor has its own overload protection.

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George Marsh

01-05-2013 15:50:55




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 Re: Compressor electrical question in reply to DH in Carolina, 01-05-2013 15:41:45  
DH, This will work providing the contacts for L1 and L3 are good and there is a path through the current sensor. I think, in a previous post Stephen said L1 was bad. Some code people may want you to use both poles on the pressure switch. I don't see an issue with your diagram.

George



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Stephen Newell

01-05-2013 16:03:52




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 Re: Compressor electrical question in reply to George Marsh, 01-05-2013 15:50:55  
There seems to be something going on with L1. I finally got it to work but its a lot harder to work than the other two manually. Anyway I get the picture and can use what ever two contacts that do work.



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George Marsh

01-05-2013 16:39:04




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 Re: Compressor electrical question in reply to Stephen Newell, 01-05-2013 16:03:52  
Stephen, There may be an issue with the current sensor too. If there is, there are 3 screws, #2,#4,#6 (T1, T2, T3). If you loosen them, you may be able to remove the bottom half, current sensors.

I'm sure the code people will sound off and tell you not remove it. My reply is there hasn't been any current sensors when you were using the pressure switch and you didn't get killed or burn up the motor. There aren't any current sensors on other air compressors either. There are only factory internal motor protectors.

Let us know if it works. There is no reason why it shouldn't, except for a bad contactor.
George

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Stephen Newell

01-05-2013 16:59:39




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 Re: Compressor electrical question in reply to George Marsh, 01-05-2013 16:39:04  
I thought the current sensor was part of the lower unit with the overload protection. There is some device that you adjust the amperage you want.



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George Marsh

01-05-2013 19:04:20




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 Re: Compressor electrical question in reply to Stephen Newell, 01-05-2013 16:59:39  
Stephen, you are right, the bottom half is the current sensor. It was designed for 3 phase, current running through L1, L2 and L3. DH thinks it may not work on single phase. He gave you the simple way to install it. I can show you how you can try to use the current sensor, but only after the experts show you how to wire it.

Wire it the way DH showed and see if that part of your contactor works. It will be simple to add in the sensor circuit.

Keep in mind there was no current sensor when you had the pressure switch installed. Never seen a small air compressor wired with a current sensor, so what's the big deal if you leave it out? Your 3 phase contactor was an after market add on.

George

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Stephen Newell

01-05-2013 20:54:53




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 Re: Compressor electrical question in reply to George Marsh, 01-05-2013 19:04:20  
All of this is more than getting the compressor running. I want to understand it and learn from it too. I can forsee having to contend with another magnetic starter in the future. I appreciate everything everybody has done for me especially you running the gauntlet with something more controversial. It wasn't what I was needing at the time but if I had the parts I might have broken one leg temporarily to use the compressor in an emergency. I had to order a replacement pressure switch so I'm not going to be doing any permanent wiring until the end of the comming week.

One thing I will never understand is why they don't just make a heavier duty pressure switch.

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Determined

01-05-2013 08:10:18




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 Re: Compressor electrical question in reply to Stephen Newell, 01-04-2013 11:05:33  
You have plenty of electrical advise on here already so I won't go further.

Have you checked the check valve between the compressor head and the storage tank?
If it is leaking it will preload the compressor pump and no matter how large your contactor is you will be overloading the motor on start-up eventually destroying it, if I recall you said you had to replace the motor once already.

Dave

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Stephen Newell

01-05-2013 08:36:16




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 Re: Compressor electrical question in reply to Determined, 01-05-2013 08:10:18  
It's more probable cold weather is the culprit as the compressor starts harder near freezing.



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Determined

01-05-2013 11:01:51




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 Re: Compressor electrical question in reply to Stephen Newell, 01-05-2013 08:36:16  
Quoting Removed, click Modern View to see

Consider trying one of those magnetic block heaters on the base of compressor head with one of those thermostatically controlled block heater extention cords powering it.

Dave



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buickanddeere

01-05-2013 06:10:47




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 Re: Compressor electrical question in reply to Stephen Newell, 01-04-2013 11:05:33  
[quote="Stephen Newell"](quoted from post at 01:10:28 01/05/13) I took the unit apart and found the model number of the coil and looked it up and found out it is a 110v coil. The long red wire is attached to one side of the coil. On the opposite side of the coil there is a contact A1. I'm wondering since the coil is 110v do I take power from L1 and run to A1 and then run the red wire to the pressure switch and out the other side to ground. I found a generic schematic online which runs the wire from L1 to L2 through the coil but I assume that would be for a 220V coil.
If I can ever get that figured out then I have the Overload Relay to figure out.[/quote

Hey stupid *ss , yes I mean you Stephen. I just got done trying to get it through your thick head before your even suggested it. That you do not use the chassis ground as a return instead of using a neutral.

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Stephen Newell

01-05-2013 07:42:44




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 Re: Compressor electrical question in reply to buickanddeere, 01-05-2013 06:10:47  
Obviously I'm not an electrician. This is why I hired an electrician to wire this thing but bubba electrician choose not to do it so now I'm stuck with trying to figure this thing out myself. I'm making mistakes but I'm going to keep studying this thing until I'm sure I have it right so try to have a little patience. The magnetic switch isn't going anywhere near electricity until I have it.



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John T

01-05-2013 05:51:41




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 Re: Compressor electrical question in reply to Stephen Newell, 01-04-2013 11:05:33  
Stephen, in wrapping up, looks like you got plenty of opinions below lay and professional (mine included, I try my best to help and give advise thats the safest possible in my professional engineers opinion), FINE GENTS HERE WHO TRY TO HELP, GOTTA LOVE THAT and thats great.

HOWEVER for your safety I strongly advise (IF THERES A CHOICE INVOLVED) you wire it according to what the true EXPERTS, the NEC advises, REGARDLES if any Billy Bobs or Bubbas here who claim they did it their own way and it works so by golly thats how its done lol. And thats true regardless if you even have any local authority or inspections or NEC etc. Im ONLY saying its SAFER if done the NEC way versus Billy Bobs non NEC method (even if Billys still works). Theres the method that WORKS and then theres the method the NEC advises which is no doubt SAFER. TAKE YOUR CHOICES I SURE KNOW MINE

PS the NEC advises certain "minimum" standards. Its is NOT law, some jurisdictiosn have adopted it some not, some older NEC versions, some the latest, I think Chicago has their own. HOWEVER their minumum standards are probably safer then if you choose NOT to adhere to them, even if the less safe method still "works" by golly

You may want to consider, at least think there just may be a possibility the panel of true professional experts who are on the NEC just might maybe perhaps possibly know more then some jack legs or anyone here myself sure included!! Ive attended their seminars taught by some of the finest minds in the electrical business HEY THE NEC PANEL ARENT ANY PUSHOVERS LOL. Think about it then wire it however you please, its your life at risk not ours.

God Bless and keep you and all here safe n sound now. ONLY YOU must decide if you want to follow the NEC method or a still works but less safe method!!!

NOT paid for by the NEC, strictly my own professional engineering OPINION and worth what you paid NOTHING........ABSOLUTELY NOTHING

John T

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Stephen Newell

01-05-2013 07:46:56




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 Re: Compressor electrical question in reply to John T, 01-05-2013 05:51:41  
I want this compressor wired correctly and safely. Now since I've learned it was originally wired incorrectly I'm going to make every effort to get it right. The magnetic starter was too dificult for me 20 years ago and since the schematics are gone off of it, its that much harder.



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jaden

01-04-2013 19:02:23




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 Re: Compressor electrical question in reply to Stephen Newell, 01-04-2013 11:05:33  
I could make you a wiring diagram if you need it. I would need the coil voltage. Coil Terminals are A1 & A2. Voltage should be listed somewhere.

Also, L1 to T2 may not show good continuity if dirty or you are not pressing the manual operator quite squarely.



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Stephen Newell

01-05-2013 04:47:58




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 Re: Compressor electrical question in reply to jaden, 01-04-2013 19:02:23  
Sorry, I missed your post. Yes I could use a diagram. I want to get this thing right. You are correct A1 and A2 are each side of the coil. Innitially I thought the coil was 110V by the model number of the coil but now I found some faint lettering on the coil itself that says 220V. There is also a minimal schematic in the owners manual of the magnetic starter which show power from L1 going through a control fuse and out to the pressure switch and back though the coil and the other control fuse to L2. I take it the control fuses are the units on the overload relay.

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George Marsh

01-04-2013 14:48:04




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 Re: Compressor electrical question in reply to Stephen Newell, 01-04-2013 11:05:33  
Stephen,
If you plan to use a magnetic switch, a contactor, the pressure switch will be used to power up the coil, not the motor. So you will need to find a contactor with a 220v coil. IF you use a 110v coil, then make sure you only run 110v to the pressure switch and wire up the contactor with 220v.

That said, when the pressure switch on my 5 hp compressor went out I couldn't find a switch rated at 5 hp. 3 hp was the largest. So I connected leg 1 of the power in to both sides of the pressure switch and both sides of the out side of the pressure switch which got connected to leg one of the motor. Leg 2 of the power got connected directly to the other leg of the motor. Basically, the pressure switch only turned on and off one side of the 220v. That was 6 years ago. Switch is working just fine.

If anyone has a source of a 5 hp pressure switch, please post. I got my 3 hp switch from grangers.
George

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buickanddeere

01-05-2013 06:15:18




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 Re: Compressor electrical question in reply to George Marsh, 01-04-2013 14:48:04  
George . Why do you delight in taking short cut farmer fixes that work but are not right? I could wire up that compressor using barbed wire and fence insulators and it would work perfectly. Would it be right?



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John T

01-04-2013 15:25:47




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 Re: Compressor electrical question in reply to George Marsh, 01-04-2013 14:48:04  
Yeppers that will "work" (at least motor will stop) but if I had ever tried that when I was an industrial electrical design engineer my boss would have fired me GRRRRRR. We ALWAYS disconnected BOTH HOT LEGS, the maintenance electricians (not to mention NEC) sorta frowned on a hot leg (120 to neutral and case frame) still being present when the motor was supposedly OFF. Of course, if done properly (and as we trained our electricians) the safety switch (in sight and within 50 feet and lockable OFF) was off and locked off BEFORE maintenance...

Take care George, it never hurts to be over safe

John T

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buickanddeere

01-04-2013 14:54:11




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 Re: Compressor electrical question in reply to George Marsh, 01-04-2013 14:48:04  
Not code legal as it leaves the motor always energized. Why not just do the job right when at it?



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John T

01-04-2013 19:35:35




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 Re: Compressor electrical question in reply to buickanddeere, 01-04-2013 14:54:11  
EXACTLY old friend, a persons life ought to be worth the price of doing it the safer and code way in my opinion, but its their life at risk not ours if thats how they want to do things???

John T



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George Marsh

01-04-2013 15:39:56




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 Re: Compressor electrical question in reply to buickanddeere, 01-04-2013 14:54:11  
Breaking one leg of 220v is done all the time. I have a 12 year old central air conditioner, Rudd, the contactor only broke one side and the other leg was wired direct. When I replaced the contactor 2 years ago, I replaced it with a 2 pole.

Look at any 220v window air conditioner. They only break one power leg. Current can't flow until the other leg is picked up.

Better tell the people who make air conditioners they are breaking the law.

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John T

01-04-2013 19:27:09




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 Re: Compressor electrical question in reply to George Marsh, 01-04-2013 15:39:56  
Dusty is right, its NOT how the NEC does it nor is it how its done for the best life safety. SURE NOTTTTTTTT HOW IT WAS DONE IN OUR SHOP. Sure do it as you please fine by me and if a manufacturer wants to skimp on safety thats his problem. Like I said it will "work" but its NOT safe nor how the NEC does it or I would ever consider doing it. Its you and your familys life and safety not mine, so do it any which way you desire.......NO WAY I WOULD JUST BREAK ONE LEG AND LEAVE A HOT ENERGIZED LEG IN THE MOTOR YIKESSSSSSSSSSSSSSSSSSSSSSSSSS LOL

God Bless and keep you safe, take care now, its YOUR life that may be saved by taking the safe route remember !!!!!!!!!

John T (A try to be safe kinda guy)

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Dusty MI

01-04-2013 16:17:58




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 Re: Compressor electrical question in reply to George Marsh, 01-04-2013 15:39:56  
Manufactures are allowed to switch only leg within an assembly. BUT it is NOT allowed in the field. Both legs MUST be switched per the National Electrical Code/NEC.

Dusty



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John T

01-04-2013 19:29:53




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 Re: Compressor electrical question in reply to Dusty MI, 01-04-2013 16:17:58  
Youre sure right and the way you suggest and the way we did it (or be fired lol) could save someones life!!!!!!!!! NO WAY I would leave a hot energized leg to the motor grrrrrrrrrrr

John T



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Stephen Newell

01-04-2013 14:37:57




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 Re: Compressor electrical question in reply to Stephen Newell, 01-04-2013 11:05:33  
OK here is the full story. When I bought the compressor 20 years ago it came with a magnetic starter. It was too complicated for me so I hired an electrician to wire the compressor. When the guy got there he said I didn't need a magnetic starter so I let him wire the compressor without it. He just put in a sub-panel with a breaker box with 8 gauge wire about 40' from the main and a 40 amp breaker. The compressor is just wired from the pressure switch to the breaker. The motor is 5hp and 22amps. Ever since then I've been burning pressure switches about one a year until I found a place I could get a 25amp pressure switch. They are lasting me about two years. Now its burned out again and in searching for a heavier duty pressure switch I came across a place that said if you need larger than 25amps you should have a magnetic starter. That got me thinking about the magnetic starter that I got with the compressor which I still have and thought I would install it on the compressor like perhaps it should have to begin with.

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John T

01-04-2013 15:18:08




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 Re: Compressor electrical question in reply to Stephen Newell, 01-04-2013 14:37:57  
If you already have a magnetic starter assuming its rated for your HP and voltage etc I would definitely use it and just let the pressure switch handle the low current to operate the magnetic switches coil as I described for you below PIECE OF CAKE and your pressure switches will last a longgggggggg timeeeeee that way. Insure the "heaters" or "thermals" in the starter are sized for your motor and find out the voltage rating of the contactors coil and wire it properly

Post back any questions

John T

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Stephen Newell

01-04-2013 16:26:56




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 Re: Compressor electrical question in reply to John T, 01-04-2013 15:18:08  
Thats the reason why I posted the thread. I thought it was a mistake to not use the magnetic starter the compressor came with. I could have wired the compressor the way it is myself. Now I'm back to square one and theres no money for an electrician at present and I'm having trouble understanding the magnetic starter. The thing is so old now there is no schematic on it anymore. The only name on it is Telemecanique D32 but there is another part of it below LR2 D2353 . So far all I know is L1 and L2 are incoming power and T1 and T2 go the the motor but I lost on the rest of it.

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Dusty MI

01-04-2013 17:15:48




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 Re: Compressor electrical question in reply to Stephen Newell, 01-04-2013 16:26:56  
Think of it as 2 separate things in the starter.
You have figured out the motor part of it.

Now the other part is the coil. First you need to find out how many volts the coil needs. That is printed on the coil, you may need to take it apart some to see that label. Think of the coil as just another motor but a very small one. That coil closes and opens the contacts of the starter, just like the air pressure closes and opens the contacts in the pressure switch.
Then have the pressure switch turn on and off that small motor/coil.
The heaters are just switches that are normally closed and open if the motor gets over loaded, and they are in series with your pressure switch, and they are already wired within the motor starter.
Most likely the coil is 220/240 volt and one side already fed from L-1 or L-2, you need to figure which.
Then take a wire from the other L- terminal to the pressure switch and another wire from the other side of the pressure switch back to feed the other side of the coil, there is a terminal for both of these wires, smaller than the L and T terminals.

If we knew where you are at someone close could help.

Good Luck,

Dusty

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Greg K

01-04-2013 19:54:39




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 Re: Compressor electrical question in reply to Dusty MI, 01-04-2013 17:15:48  
This was assuming the coil is 240V. If it is 110V coil you will need a Neutral to the one side of the coil and feed the pressure switch with one hot leg which then goes to the loose red wire.



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Stephen Newell

01-04-2013 19:44:57




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 Re: Compressor electrical question in reply to Dusty MI, 01-04-2013 17:15:48  
I finally determined that L1 is working. I just wasn't manually working it hard enough. It turns out the coil is a 110V and the loose red wire is connected to the coil.



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Stephen Newell

01-04-2013 18:07:25




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 Re: Compressor electrical question in reply to Dusty MI, 01-04-2013 17:15:48  

Thanks for the help. This thing was why I hired an electrician in the first place and the guy didn't do it. I've been sitting here this evening probing the switch with an ohm meter trying to make some sense of it. For some reason L1 isn't doing anything. L2 and L3 work T2 and T3. The bottom part of this thing has a dial where you can adjust the amperage and is set on 26amps. The right side has a reset button. I don't know which side of it has the coil. Here is a picture of it.

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George Marsh

01-04-2013 20:18:45




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 Re: Compressor electrical question in reply to Stephen Newell, 01-04-2013 18:07:25  
Stephen,
Has anyone answered your question how to wire the contactor in the pic? What you have is a 3 phase contactor. L1,L2,L3 = 3 phase. It is possible this contactor was used on 3 phase 440v making the coil 440v. Is there any info about the coil?

This is only a guess, need to confirm with an ohmmeter. The red wire is a part of the control circuit. One control leg from the pressure switch will feed in on the long red wire, goes to NC, normally closed contact, which will open if the bottom section measures too much current. The power then is sent to T4 via the other short red wire. My guess is T4 is one side of the control coil. Now use your ohmmeter and try to determine which screw is the other side of the control coil, I would try T3. If it is T3, that will be the other wire going to the pressure switch.

If there is no info about coil voltage, make up a cord and apply 220v to the coil. Going to say that if you get it right, the blue section will pull inward when the coil is energized.

Then all you need to do is apply 220v to L2 & L3 and wire T2 & T3 to motor.

Now, don't forget to put all this inside an approved electrical box or the NEC COPS will give you a ticket and push you over a cliff.

If you can't get the contactor to work and you find out how much one is going to cost you may want to double up the switch like I said above. Then put the all air compressor inside a metal container, turning it into an appliance. Then make and break one side of the 220v. The metal container will make it safer, NEC approved appliance. You may want to put a grounding rod on the metal box too. Wouldn't want to upset the NEC cops.

By the way, a code is not the same as a law, except here. You can be arrested if you break a law. Never seen anyone get arrested for breaking an NEC code. If you could, I would be serving a life sentence.

George

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Stephen Newell

01-04-2013 21:10:28




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 Re: Compressor electrical question in reply to George Marsh, 01-04-2013 20:18:45  
I took the unit apart and found the model number of the coil and looked it up and found out it is a 110v coil. The long red wire is attached to one side of the coil. On the opposite side of the coil there is a contact A1. I'm wondering since the coil is 110v do I take power from L1 and run to A1 and then run the red wire to the pressure switch and out the other side to ground. I found a generic schematic online which runs the wire from L1 to L2 through the coil but I assume that would be for a 220V coil.

If I can ever get that figured out then I have the Overload Relay to figure out.

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George Marsh

01-05-2013 03:48:14




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 Re: Compressor electrical question in reply to Stephen Newell, 01-04-2013 21:10:28  
Stephen,
Here is the deal, what I tell you the NEC cops will tell you is wrong, you are going to blow up the world, kill someone, kill yourself, get a ticket for breaking the law and so on.

Then the advice I'm going to give you is worth what you are paying for it......

Secondly, the contactor you have is not the one that came with the air compressor. It is something so one got off a 3 phase device.

That said, the bottom half of your motor contactor is not set up for your motor and I would remove it using only the top contactor. Again, NEC cops will jump all over me for saying this.

I would get an extension cord and wire it to your pressure switch. Black wire on one side and white wire on the other side of the pressure switch. Use the ground wire if your 220v wire is not already grounded to the compressor. Then send the black wire from the other side of the pressure switch to A1 and the white wire to the other side of the coil. Plug in extension cord and see if contactor pulls in. If it does, you are half way home.

Wire the 220v to L2 & L3 and the motor to the terminals below T2 & T3.

Forget the overload protection on the contactor. I've never seen a motor that didn't already have it's own overload protection. Make sure your circuit breakers are the right size for your wire. Put the contactor in a metal electrical box. You should be good to go.

Hope I've been a help. Let me know if it works.
George

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Stephen Newell

01-05-2013 05:03:32




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 Re: Compressor electrical question in reply to George Marsh, 01-05-2013 03:48:14  
It may perhaps be the wrong magnetic starter for my compressor but I bought the compressor new directly from Ingersol Rand and that was the switch that came with it. The motor however went out a few years back and was replaced. You are right the new motor has its own overload protection where I don't think the original motor did. I did give out some bad info about the coil being 110v. I have since learned it is 220V. I also do need to be careful not to energize the compressor itself. The compressor is used outdoors where the ground often gets wet around it. All in all with everybodies help, I'm getting closer to understanding this unit. Thankyou.

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Greg K

01-04-2013 19:46:12




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 Re: Compressor electrical question in reply to Stephen Newell, 01-04-2013 18:07:25  
It looks to me like the 2 red wires are going through yur motor overload contacts. These wires need to be hooked up in series with the coil wires, so if the overload trips out it will not let the coil on the starter kick in. so from t2 there needs to be a wire to the pressure switch, from the other side of the pressure switch it hooks to the red wire that is loose on one end. Now from t3 there needs to be a wire the same size as the two existing red ones to the other side of the coil wire, I believe this terminal to be on the top right corner of the starter but NOT visible in the picture. Terminals 13 and 14? are just an auxiliary set of contacts and not used in this application. Now the feed goes to terminals L1 and L2 as was stated earlier. The motor leads connect to T2 and T3. When you press in the button on the cover of the starter box it will press the contacts together completing the circuit from L1 to T1 and L2 to T2. Also energizing the wires fromT2 to the motor overload contacts, through the contacts through the pressure switch(assuming it is calling for the need for power), and to the latching coil in the Starter. It will also complete the circuit from T2 to the other side fo the coil. This is assuming that there is a pushbutton on the case to depress the starter initially. If there is no push button, then the red wire that is not connected on one end should hook to one side of the pressure switch. The other side of the pressure switch will hook to L3. Now there will need to be a wire from L2 to the other terminal on the coil, which I believe to be on the upper right hand corner, but not in the picture. With this setup you will need a disconnect in sight of and within 50 foot of the compressor for sure.

If you could take some pictures of the sides of the starter it would help. Clear as mud now? Greg

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Stephen Newell

01-04-2013 21:48:17




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 Re: Compressor electrical question in reply to Greg K, 01-04-2013 19:46:12  

The pressure switch itself had a cut off on it and the sub-panel and breaker for the compressor is 3' away. Do you think I need a disconnect also? Here are the pictures of the sides of the starter. Also there is another of the overload. The flash on the camera tends to bleach the picture. The right side of it has the letters NC on it with the numbers 95 and 96 on it.

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Greg K

01-05-2013 06:45:53




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 Re: Compressor electrical question in reply to Stephen Newell, 01-04-2013 21:48:17  
No disconnect neededif the panel is only 3' away. I cannot see on this but I believe the other terminal to your coil is on the upper right corner, to the right of L1, L2,L3, but below 14. About in the same location of where the short red wire goes. I don't see anything on the labels that lead me in a different direction. George March is correct in that it is a 3 phase starter, however T1, T2, T3 are all motor leads and not a coil terminal, just as L1, L2, L3 are all input leads for 3 phase power. Gotta go to work now, but try and get me a pic of the top right looking down from the top and this will verify how wrong or right I am.

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Stephen Newell

01-05-2013 08:03:33




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 Re: Compressor electrical question in reply to Greg K, 01-05-2013 06:45:53  
Looking at the top of the switch under L1 there is A1 which is one side of the coil and below 13 and 14 is A2 which is the other side of the coil.

I expected the switch was made so it could either be used for single phase or three phase.



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Stephen Newell

01-05-2013 03:47:20




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 Re: Compressor electrical question in reply to Stephen Newell, 01-04-2013 21:48:17  

Maybe you can see the labels better with these pictures.



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Greg K

01-04-2013 19:55:45




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 Re: Compressor electrical question in reply to Greg K, 01-04-2013 19:46:12  
Oops posted that reply about the 110v coil in the wrong spot. It should be here



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David G

01-04-2013 14:03:54




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 Re: Compressor electrical question in reply to Stephen Newell, 01-04-2013 11:05:33  
I have a 5HP single phase that only has a pressure switch.

Are you sure it is unloading?

what upstream breakers or fuses do you have?



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Stephen Newell

01-05-2013 08:47:52




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 Re: Compressor electrical question in reply to David G, 01-04-2013 14:03:54  
It is unloading and the compressor is wired to a 40amp breaker. I think the problem at present is the compressor starting in cold weather and it's too much startup power for the pressure switch. The magnetic starter will handle more power.



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John T

01-04-2013 12:11:45




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 Re: Compressor electrical question in reply to Stephen Newell, 01-04-2013 11:05:33  
If youre constantly burning up pressure switches ITS HP AND/OR CURRENT RATING MY WELL BE LESS THEN THE 5 HP YOU REQUIRE???????? The pressure switch may well be a low current rated device (designed to operate a seperate independant magnetic starter coil) and NOT switch and operate the 5 HP motor itself!!

Of course it takes much more current to START that compressor then to run it, and when those contacts just close they must handle that current ya know.

HERES THE DEAL: You could use a magnetic starter which has sufficient HP and Current rating to start and run the compressor motor, AND JUST USE THE PRESSURE SWITCH TO CONTROL THE STARTERS CONTACTOR which is wayyyyyyyyy less current then the actual motor requires. The pressure switch would ONLY activate the starters low current coil, which when activated and conducting VIA THE PRESSURE SWITCHES CLOSURE then closes the higher HP and higher current rated magnetic motor starter contacts...

A tyical farmer Billy Bob installation could be a wall mounted 2 pole Safety Switch,,,,,,,,,,which feeds the magnetic starter,,,,,,,,,which is controlled on and off via the closed contacts (and low current) inside the pressure switch.

ORRRRRRRRRR when I designed such at our industrial facility I USED A COMBINATION STARTER INSTEAD. It consisted of a combination single enclosure safety switch PLUS a magnetic starter all in a single enclosure and was cheaper then buying BOTH seperate safety switch and seperate magnetic starter

NOTE a magnetic motor starter will have whats called "heaters" or "thermals" sized for the motor to protect against overload and overheating. Size them to match your motor HP, Voltage, Amperage. ALSO the starters coil voltage (which pressure switch activates by its open and closing) can be same as your operating voltage or less (240 or 120 or even lower like 24 etc)

Buttttttttttt if the pressure switch is big enough and the above is NOT the problem, look for excess current especially excess start up current, caused by too long of wire runs or excess voltage drop or too small of wire or a faulty compresor head pressure unloader etc

John T

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buickanddeere

01-04-2013 11:56:52




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 Re: Compressor electrical question in reply to Stephen Newell, 01-04-2013 11:05:33  
Neither. Line power from a local shut off switch or wall receptacle to the line side of the magnetic starter. Load side of be starter to the motor. Control power from the line side of the starter to the pressure switch and back to the coil, through the overload contacts. Coil voltage must match line voltage . Don't be one of those d!cks that use the 240V supply to the coil and wire to ground to obtain power for a 120V coil. Time to hire a pro before you burn the place down, cripple or kill somebody. You hire a pro to do your dental work .

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Ken Macfarlane

01-04-2013 13:48:12




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 Re: Compressor electrical question in reply to buickanddeere, 01-04-2013 11:56:52  
Those little step down transformers for 240-120 are common and handy as a lot of stuff uses 120 V control voltage. Like he said, ground wires are not there for you to wire into a circuit.



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Ken-Pa

01-04-2013 11:51:36




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 Re: Compressor electrical question in reply to Stephen Newell, 01-04-2013 11:05:33  
Are you using the correct magnetic safety switch ? Wiring goes thru the safety switch , then pressure switch to motor . Make sure you"re using the correct amperage wiring & breaker also . Its been several years since I"ve done any compressor installations , so I"ve forgotten a lot . You also need to take into consideration how far the compressor is from your main source of power due to voltage drop . Remember 8 ga wire is good for up to 40 amps & 6 ga is for 50 amps . I generally used 6 ga wire from breaker to compressor magnetic safety switch & then 10 ga from there thru pressure switch to motor . I"ve never had any of my installations fail to this day (PTL). I used to be a registered installer for a couple compressor companies . So if the purchaser wanted their compressor warranted by the manufacturer , it had to be installed by me . But of course we did have a couple purchasers try collecting on a warranty issue but lost out when they couldn"t produce my installation paper work . That also saved my butt & reputation back then . I have drawings somewhere of how I used to wire up large compressors if interested & I can locate them . But it"s been 20+ yrs so I can"t guarantee my locating them . Let me know if this helped you any . You might check with your local industrial electrical supplier for help & maybe a drawing of wiring . Just be safe . Make all connections tight & secure . Remember you will have vibrations to contend with . God bless , Ken

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