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3 phase Air Compressor wiring - Magnetic starter.


 
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DFZ
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PostPosted: Wed Apr 17, 2013 10:53 pm    Post subject: 3 phase Air Compressor wiring - Magnetic starter. Reply to specific post Reply with quote

Trying to sell a used 15 year old air compressor for a friend. I figured I could get more money out of it if the buyer hears it run. It was wired for 3 phase high voltage (460v?). Our shop has the lower voltage 3 phase. Really easy to swap the motor around and run 3 phase 230v so I did.

The question is, does the magnetic starter need to be changed to match the voltage?

The magnetic switch just buzzes when I try to start it, but if I press in the plunger on the starter the motor starts and compressor works just fine. Or maybe the magnetic starter is just broken.

If the magnetic starter does need to be changed, would it be best to try and sell the compressor without letting the buyer hear it run, or let the buyer hear it run by pushing in the plunger and warning them they would need to change the magnetic starter / and or switch the motor voltage back? I think I found the starters on Ebay for as low as $30, maybe it would be worth it to switch it.

Thanks for any advice.

Photo of the magnetic starter:


 


Last edited by DFZ on Wed Apr 17, 2013 11:02 pm; edited 1 time in total
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buzzinduzzin
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PostPosted: Thu Apr 18, 2013 1:30 am    Post subject: Re: 3 phase Air Compressor wiring - Magnetic starter. Reply to specific post Reply with quote

the holding coil (electromagnetic device) that closes the points is probably gonna need changed to match the new lower voltage. they are not very expensive
 
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Bill in IN
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PostPosted: Thu Apr 18, 2013 1:39 am    Post subject: Re: 3 phase Air Compressor wiring - Magnetic starter. Reply to specific post Reply with quote

You will also need to change (adjust) the heaters in the overload block.
 
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Stephen Newell
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PostPosted: Thu Apr 18, 2013 3:27 am    Post subject: Re: 3 phase Air Compressor wiring - Magnetic starter. Reply to specific post Reply with quote

If the heating coil is the part at the bottom, I have one I don't need anymore. My compressor is single phase and it was recommended I not use it.
 
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John T
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PostPosted: Thu Apr 18, 2013 3:43 am    Post subject: Re: 3 phase Air Compressor wiring - Magnetic starter. Reply to specific post Reply with quote

I agree with the fine gents below. Although Ive been retired for years as an electrical design engineer, when I specified magnetic motor starters they were available in different hold in coil voltages (both low and high voltage)REGARDLESS of the voltage of the motor. Therefore perhaps the voltage now being applied to the coil is too low to engage the relay so see if you can replace the coil in your starter ????? with a 230 volt (if thats where youre now operating).

Similar the thermal overloads (heaters as they are called) need to be sized to protect the motor so if youre now operating at 230 versus 460 volts they also need to be changed and they should be readily available in the new current rating your motor requires.

The starter relay contacts (NOT talking about the hold in coil now but the actual high current contactor) have a certain HP and current rating, so since you have increased the current by operating at a lower voltage just be sure the starter is suitable.

I always specified a lockable either fused disconenct (safety switch) in sight and within 50 feet of a compressor if a seperate magnetic starter was used or else a combination starter and, of course, flex conduit for the final motor connection.

John T NO WARRANTY its been toooooo long since I did this as a profession and Im rusty on the latest codes
 
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Chris(WA)
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PostPosted: Thu Apr 18, 2013 4:23 am    Post subject: Re: 3 phase Air Compressor wiring - Magnetic starter. Reply to specific post Reply with quote

Looks like you are pulling control power off the top two lines gong into the starter. If so you may not have enough voltage to the circuit. If it feeds a transformer, see if you can retap it for lower voltage.
 
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Dusty MI
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PostPosted: Thu Apr 18, 2013 4:34 am    Post subject: Re: 3 phase Air Compressor wiring - Magnetic starter. Reply to specific post Reply with quote

I'm going to stick my neck out on this.
Because it is only temporary, only so a buyer can see it run, and NOT put it into service, I would just hook it up to a disconnect and start/stop it by hand. Most likely the pressure switch will not work, so just turn in on to show that it runs and pumps air, then shut it off.

I repeat, DO NOT LET IT RUN VERY LONG.
 
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John T
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PostPosted: Thu Apr 18, 2013 4:55 am    Post subject: Re: 3 phase Air Compressor wiring - Magnetic starter. Reply to specific post Reply with quote

Go ahead my sparky friend, stick your neck out there lol dont be afraid!!!!!!!! I tend to agree if all he wants to do is see it run a short period hook it up direct no need for temporary thermal overload protection, provided he has a quick manual disconnect method handy

John T
 
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missouri massey man
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PostPosted: Thu Apr 18, 2013 5:27 am    Post subject: Re: 3 phase Air Compressor wiring - Magnetic starter. Reply to specific post Reply with quote

All coils will have the coil operating voltage on a tag somewhere on the side of them. They are inexpensive and easily changed. First you should check for what that voltage is against what is required and do what is necessary to get it to match.

This starter in particular has no replaceable "heaters" like the old ones that had to be changed to match the amp draw. See the little white arrow point at the 6:00 position under that little radial switch? The setting is above the arrow. Read the nameplate amp draw on the motor relative to the voltage you are operating it on then rotate the dial to match that amperage.

The little blue button is a manual/automatic reset switch. Typically set it to the manual position so it has to be physically reset.

Try FactoryMation at 1 800 972 0436 for the correct coil. Hopefully they will handle the brand. If not WW Grainger would be a good one to try. It is an ABB brand.

Pushing in the contactor squarely for a short time to hear it run will not hurt anything providing the motor is wired correctly for the applied voltage. Good Luck. By the way, it looks like the control's reset is tripped in the picture. Just push it in and you should feel a little "click".
 


Last edited by missouri massey man on Thu Apr 18, 2013 5:30 am; edited 2 times in total
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DFZ
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PostPosted: Thu Apr 18, 2013 7:29 am    Post subject: Re: 3 phase Air Compressor wiring - Magnetic starter. Reply to specific post Reply with quote

Thanks for the advice everybody. I think I might just run it as it is, advertise it as wired for high voltage, and change it back before they take it. It only takes 2 minutes to change the motor wiring.
 
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XRogerX
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PostPosted: Thu Apr 18, 2013 1:51 pm    Post subject: Re: 3 phase Air Compressor wiring - Magnetic starter. Reply to specific post Reply with quote

As you have now doubled the amps going through that starter, I would highly recommend that you ensure it can take that amount of current if you are advertising it as being ready to hook up and go. Same goes for the wire gauge. I"d be tempted to sell it without any electrical accoutrements just to ensure nothing could come back to haunt you. I have seen some pretty dodgy wiring setups, one guy had two phases going through a pressure switch with the third hard wired into the motor live.
 
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