Wiring a Motor Starter and Pressure Switch

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  #1  
Old 03-20-11, 08:25 PM
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Question Wiring a Motor Starter and Pressure Switch

Installing a compressor (240V 1Phase, HP unknown). Where I'm at now, is at the starter panel and I know this much, L1 and L2 are power in (both hot legs) and the T terminals are motor power. As far as the pressure switch power in, IDK where the legs are to be installed. I'll get a pic of the starter here in a bit.

Any help is much appreciated.
 
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Old 03-20-11, 08:41 PM
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Pic of switch:

 
  #3  
Old 03-21-11, 11:13 AM
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The operating coil has one lead connected to one of the Line terminals with the other lead at a terminal for connection to the control device.

I'll guess that terminal "3" is this connection point . It's possible to locate where the coil leads connect using a multimeter that can accurately measure Ohms. Your most important concern is connecting the pressure switch directly across two Line terminals which will result in a "Dead" 220 volt short -circuit.

Good Luck , and Learn & Enjoy from the experience.
 
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Old 03-21-11, 11:00 PM
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I had an electrician look at it (real good buddies w/ him) and he said to run a jumper from L1 to the terminal next to 2, then run a wire from L2 to the pressure switch, then from the pressure switch to the terminal next to Z. I did that, and both the wire going to the pressure switch were live (120V). I touched them together before I checked them, and naturally the motor started didn't do anything.
 
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Old 03-22-11, 12:18 PM
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The safest method for locating the connection points for the Pressure Switch is using a digital multimeter than can measure "Ohms". If you don't have one , buy a low-priced model.

You problem may be complicated by the Overload devices which will open the circuit to the Operating Coil if the motor draws excess current . If these OL's are not completing the circuit of the Operating Coil which connects to the external wiring , there is an "open" in the internal wiring of the Starter. This possible problem could be determined with a Ohmmeter which can check for an open / closed circuit .
 
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Old 03-22-11, 12:35 PM
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What is the voltage of the holding coil?
 
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Old 03-22-11, 02:31 PM
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I'm not sure. Only voltages I seen were 208/240V somewhere on the switch, and the coil had 120 on both sides.
 

Last edited by bigskyram; 03-22-11 at 03:52 PM.
  #8  
Old 03-22-11, 03:20 PM
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This isn't rocket science. Your starter may have one, or more, "auxiliary" switches that actuate when the starter is energized but for the pressure switch "pilot device" these would normally not be used. The coil (or possibly the label) will denote the coil voltage and unless it is the same as the supply voltage you will need a transformer to convert from the supply voltage to the coil voltage.

The contacts of the pressure switch, the motor starter coil and the overload devices pilot contacts will all be in series and this series in parallel with the supply voltage or transformer secondary. You need the proper "heaters" on the overload devices and the resets need to be firmly pressed in AFTER mounting the heaters to close the O/Ls pilot contacts. Remember that most pressure switches have two sets of double-break contacts and that you will only need to use one set but be sure to use the Line and Motor (or Load) contacts of the one set.

If you could post several more CLEAR pictures of the starter I might be able to give a more detailed response.
 
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