Motor starter ladder diagram help

Discussion in 'Homework Help' started by Hmagers04, Feb 13, 2016.

  1. Hmagers04

    Thread Starter New Member

    Feb 12, 2016
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    I just need someone to verify that I'm completing my assignment correctly. I have not yet included line and cross-reference numbers on the diagram so disregard that i'll work on it later. This is what needs to be included in my ladder diagram..

    A 3-phase motor is to be protected against phase loss, phase imbalance, or low voltage using a Square D MPS type relay. The motor is to be controlled from a START/STOP PB station that also contains a green pilot light to indicate the status of the MPS relay. The MPS is to be supplied power form the line side of the starter. Include line and cross-reference numbers on the diagram.
    The green status light should be ON when the 3-phase, 240-volt motor circuit and the MPS are energized. The motor is not to be started unless the status light is illuminated. This ON status indicates that a phase reversal has not occurred in the circuits on the line side of the starter.

    Available equipment list:
    Motor starter
    - With holding contacts - 240 VAC coil -1NC/1NO Aux. contacts

    START/STOP PB station
    - With 12 VDC green light
    240/480 x 120/240 V transformer
    MPS relay with 240 input
    120 VAC to 12 VDC power supply
    - With battery backup
    Control relay – 12 VDC
    - 2NC/2NO sets of contacts
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Initially puzzled why you have the motor contactor on the power side rather than control circuit side of the transformer?
    It would be customary to use a 120v or control voltage value version rather than the 240v supply type.
    Max.
     
  3. Hmagers04

    Thread Starter New Member

    Feb 12, 2016
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    This is the ladder diagram they selected for us....So we have to fill it in based on what they provided
     
  4. MaxHeadRoom

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    Jul 18, 2013
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  5. Hmagers04

    Thread Starter New Member

    Feb 12, 2016
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    That short was my error, it shouldnt be there. I believe that the M is supposed to be the motor coil??
     
  6. Hmagers04

    Thread Starter New Member

    Feb 12, 2016
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    Or the motor starter coil
     
  7. Hmagers04

    Thread Starter New Member

    Feb 12, 2016
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    Thats why I find it a little confusing....I dont understand how im supposed to have a 12vdc pilot light light up when the 240v MPS is energized
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The secondary of the transformer is 120v and you also have a contact across that, there always has to be a load (output) shown for any logic string otherwise it is a dead short.
    Prmary and secondary should also sh0w fusing.
    Refer to some of the Dwg's in the PDF.
    Max.
     
  9. Hmagers04

    Thread Starter New Member

    Feb 12, 2016
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    Thanks for all of the input
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Incidentally the string with the CR relay in is shown wrong, the coil always is shown as the last in the string, and not in series with another output, light, loads can be shown in parallel but always at the end.
    Max.
     
  11. Hmagers04

    Thread Starter New Member

    Feb 12, 2016
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    Wow...I had this ladder diagram all sorts of screwed up then...Thanks again for correcting me...
     
  12. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Can you post the instructions as they were given to you?
     
  13. Hmagers04

    Thread Starter New Member

    Feb 12, 2016
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    The PDF attached bellow is what they gave me
     
  14. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Take another crack at solving it, the print also shows an error of the 12vdc connected to the 120vac.
    Max.
     
  15. Hmagers04

    Thread Starter New Member

    Feb 12, 2016
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    I will, I emailed IEC about their error in the print.
     
  16. Hmagers04

    Thread Starter New Member

    Feb 12, 2016
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    Modified my ladder diagram...
     
  17. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I will give the once over, but off the bat there are errors again with contact in rungs without outputs, and unlabeled!.
    It is now considered bad practice to place an O/L in the opposite side to the coil.
    It is mainly when the right side rail is a grounded neutral, but it still pays to keep all logic on one side of the output.
    In most case the X1 terminal would be grounded to set up a local neutral. But not mandatory.
    Also the use of a bridge is not necessary if you place the light on the 12v DC side of the circuit.
    You have been given a 12dc ind light.
    Max.
     
    Last edited: Feb 14, 2016
  18. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Here is a NFPA79 example of control wiring.
    Max.
     
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