User Tag List

Page 1 of 2 1 2 LastLast
Results 1 to 10 of 11

Thread: Multiple motors and switchable disconnects

  1. #1
    Join Date
    Jun 2019
    Location
    Concord, CA
    Posts
    7
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Multiple motors and switchable disconnects

    I have a 90 amp sub and it's feeding 4 motors, 1 of which is a phase converter that feeds 2 of the 4 motors itself. The hp rating of the phase converter is 5hp, 3 phase, 230/460 v, 1800 rpm's. It's powering a 2 1/2 hp, 3 phase, 460 FLA motor. The other motors are a single phase, 220v 5hp motor and a single phase, 129v, 5.6 amp motor with a PF of 92%. My question is I can't possibly run all these motors at the same time with a 90 amp panel and the panel also feeds lights and plugs in this commercial wharehouse as well. Is there a way to hookup a disconnect or set of disconnects that would only allow the operation of one of the motors listed above to be powered up at a time? Ensuring that 2 motors could not be turned on at the same time.

  2. #2
    Join Date
    Jun 2019
    Location
    Concord, CA
    Posts
    7
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Multiple motors and switchable disconnects

    How do you set up a series of disconnects that will only allow 1 of your 5 motors to run at any given time? Allowing more than 1 to run at a time would create a draw of more amps than the sub panel supplies and overdraw it. Is this even possible without upgrading my service, which is 90 amps currently?

  3. #3
    Join Date
    Jul 2006
    Location
    San Francisco Bay Area, CA, USA
    Posts
    8,853
    Mentioned
    2 Post(s)
    Tagged
    0 Thread(s)
    I would use contactors and a smart relay (or a bunch of relay logic) to only allow one circuit to be energized at a time.

    Or use a rotary selector switch with 5 positions so that power can only go to the one you select with that switch.
    __________________________________________________ ____________________________
    Many people are shocked when they discover I am not a good electrician...

  4. #4
    Join Date
    Apr 2019
    Location
    Union, KY, USA
    Posts
    303
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by samkeary View Post
    I have a 90 amp sub and it's feeding... I can't possibly run all these motors at the same time with a 90 amp panel...
    Is this by actual test, or your calculation? It sounds like the panel is actually in place and working. Is this one of those things where everyone 'knows' not turn on more than one-at-a-time? And someone did turn on more than one and caused problems??

    And you -have- to run at least 2 at some times-- Motor #1 is a phase converter that feeds motors #2 and #3 (although I'm assuming #2 and #3 can't run at the same time).

  5. #5
    Join Date
    Apr 2019
    Location
    Union, KY, USA
    Posts
    303
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Look at some of the lockout switches for the home generator ATS market-- they're designed to interlock two switches in a home panel, allowing only 1 to be 'ON' at once.

  6. #6
    Join Date
    Jul 2006
    Location
    San Francisco Bay Area, CA, USA
    Posts
    8,853
    Mentioned
    2 Post(s)
    Tagged
    0 Thread(s)
    Please done cross post. Duplicate threads have been merged.
    __________________________________________________ ____________________________
    Many people are shocked when they discover I am not a good electrician...

  7. #7
    Join Date
    Jun 2019
    Location
    Concord, CA
    Posts
    7
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by PaulMmn View Post
    Is this by actual test, or your calculation? It sounds like the panel is actually in place and working. Is this one of those things where everyone 'knows' not turn on more than one-at-a-time? And someone did turn on more than one and caused problems??

    And you -have- to run at least 2 at some times-- Motor #1 is a phase converter that feeds motors #2 and #3 (although I'm assuming #2 and #3 can't run at the same time).
    The panel is in place and working but these extra motors are being added to a workshop that previously had one or two small motors and now needs to accommodate 5 motors and initially turning on 2 or more of these new motors, caused nuisance tripping and tripped not just the sub but the main as well.

  8. #8
    Join Date
    Jun 2019
    Location
    Concord, CA
    Posts
    7
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Jraef View Post
    I would use contactors and a smart relay (or a bunch of relay logic) to only allow one circuit to be energized at a time.

    Or use a rotary selector switch with 5 positions so that power can only go to the one you select with that switch.
    Which of these two options is 1. cheaper and 2. easier to set-up?

  9. #9
    Join Date
    May 2019
    Location
    Chicago, IL
    Posts
    121
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    One alternative along the lines of what Jraef mentioned is below and uses commonly available parts:

    Use an appropriate contactor and a start/stop switch for each of the 5 motors, but with the same coil voltage in all of them (for example, either 120V or 208V).
    3 SPDT switches are used to select which of the motors can be activated by their local start/stop switch. The connections below will also not allow either 3PH motor contactor to be turned ON with its start switch unless the contactor for the phase converter is turned on first with its own start switch.

    Switch 1:
    Common terminal to 120V line
    Position 1 selects 1PH motor operation. Supplies 120V to the switch 2 common terminal.
    Position 2 selects 3PH motor operation. Supplies 120V to the start/stop switch for phase converter.

    Switch 2:
    Common terminal is supplied with 120V when switch 1 in position 1.
    Position 1 selects 1st 1PH motor. Supplies 120V to start/stop switch for this motor.
    Position 1 selects 2nd 1PHmotor. Supplies 120V to start/stop switch for this motor.

    Switch 3:
    Common terminal connected to the start/stop switch output that activates the coil on phase converter contactor.
    Only at 120V when phase converter is running.
    Position 1 selects 1st 3PH motor. Supplies 120V to start/stop switch for this motor.
    Position 1 selects 2nd 3PH motor. Supplies 120V to start/stop switch for this motor.


    If the switches are physically located as below I think it would mentally simplify the selection of the different types of motors, because switch 2 is enabled when switch 1 is UP and switch 3 is enabled when switch 1 is DOWN:
    Switch 2
    Switch 1
    Switch 3
    Last edited by synchro; 06-14-19 at 12:54 AM.

  10. #10
    Join Date
    May 2019
    Location
    Chicago, IL
    Posts
    121
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    In my post above, where "Position 1" is mentioned a second time under switches 2 and 3 it should be "Position 2".
    "This was late last night" is my lame excuse.
    Last edited by synchro; 06-14-19 at 09:34 AM.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •