Motor Starter Question

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  #1  
Old 03-28-11, 05:56 PM
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Motor Starter Question

Hi, I'm installing a 3 phase 220 volt motor starter for a compressor with a 5hp motor.
I know the power goes on L1, L2, L3. The coil is a 220 volt coil. Question is, where do I get the 220 volts for the coil from? Do I need to run a separate 220 circuit for it or can I rob it from two of the phases. The pressure cutoff switch on the compressor will be the on/off for the coil.
Thanks for your help.
Joe
 
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  #2  
Old 03-28-11, 06:29 PM
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Do you know if you have a delta or star supply?

I can't help much beyond that but answering my question may help the pros help you.
 

Last edited by ray2047; 03-28-11 at 07:03 PM.
  #3  
Old 03-28-11, 10:05 PM
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No, you don't need or even want a second circuit for the "pilot" duty.

Is this going to be in a true three-phase system? Three-phase motor starters are used in single-phase systems all the time. If you are using a converter to change single-phase to three phase it is better to wire the starter pilot circuit as if it were being used on single-phase.

Post back with answers to my questions and if possible CLEAR detailed pictures of the starter. Is this going to be connected with a Hand-Off_Auto selector and a pressure switch or just the pressure switch.

And by the way, I doubt very much if the supply voltage is 220 volts. If true three-phase it is either 208, 240 or 480 volts. If derived through a converter fed from a standard single-phase system it will be 240 volts. It is well into the second generation (if not the third) since the utilities have supplied 220 and 110 volts. I don't even remember when the nominal voltages were 220 and 110 and I'm 60 years old!
 
  #4  
Old 03-28-11, 10:40 PM
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I am with Furd and do you have true three phase supply or using the phase converter { static or rotary } that may make the diffrence on the connection for safety issue.

I have couple diagrams to use but right now I will wait until you give us more details what Furd asking for that will make the diffrence there.

And be aware with triphase motour they can run backward or forward by chaning either two phase conductors.

As far for voltages the 208 is star { Wye } while the 240 typically Delta and 480 volts can go either way.

so please post us the details the more info you can give us the more you will get the answer.

Also if you have triphase load centre you may want mention the brand name as well { some older load centre may not have any replacement breakers}

Merci.
Marc
 
  #5  
Old 03-29-11, 03:40 AM
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Hello, Thanks for getting back to me.
This is a star (wye) 3 phase system and the voltage is 208/3 phase.
The panel is 120/208 and it's fed from a 277/480 source.
It's a Square D motor starter NEMA Size 1. and the coil on it says 240volts 60hz and 220 volts 50hz. the coil number is 31041-400.
I uploaded the picture for this motor starter to:
ImageShack® - Online Photo and Video Hosting

Thanks,
Joe
 

Last edited by JMS124; 03-29-11 at 05:51 AM.
  #6  
Old 03-29-11, 10:34 AM
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Three-phase starter pilot circuits (what actually controls the motor starter) are usually wired from L1 through the pilot device (pressure switch in your case) through the coil, through the three overload relays and then back to L3. If you add the H-O-A switch it becomes a bit more complicated but still follows the same scheme.

Your starter probably has the wiring from the coil through the O/Ls back to L3 installed and it may have a wire from the coil going to a "holding contact" (small switch mechanically linked with the main moving part of the starter) for use with a "start-stop" pushbutton arrangement. The photo is not clear enough to determine.

There should be a wiring diagram pasted in the back of the cover for the enclosure along with instructions on how to connect either a momentary or maintained pilot device. You want the maintained pilot device diagram. You might need to replace the coil with a 208 volt model if it doesn't "pull in" smartly.

BTW, if the primary service to the site is 480Y/277 then you must have an intermediate transformer to drop the voltage to the 208Y/120 panel.
 
  #7  
Old 03-29-11, 07:22 PM
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There one very important part you should be aware as Furd mention H-O-A that switch is only used if you have automatic unloader valve for contionous run if this type of valve not located in the compressour itself then you can not use the H-O-A the only way you can do this is use the on- off swtich or use the toggle switch in switch box in series of coil circuit that will cut off when you turn the switch off.

There are few ways to do this in safe manner.

Furd part is one of them I used as well.

And the other thing when you run on 208 volts supply you may want to double check the heater and motour nameplate to make sure you will not trip out early due the 208 volt will draw just little more current than what it was on 240 volts so again check the cover it will have listing of heater size Vs. current drawage on the motour load.

we will fill you more detals once we know where you go with this and also please take a photo of compressour itself so we will know which type you have there.{ due some are constant run type }

Merci.
Marc
 
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