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    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
    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?

    Comment


      #3
      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...

      I'm in California, ergo I am still stuck on the 2014 NEC... We'll get around to the 2017 code in around 2021.

      Comment


        #4
        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).

        Comment


          #5
          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.

          Comment


            #6
            Please done cross post. Duplicate threads have been merged.
            __________________________________________________ ____________________________
            Many people are shocked when they discover I am not a good electrician...

            I'm in California, ergo I am still stuck on the 2014 NEC... We'll get around to the 2017 code in around 2021.

            Comment


              #7
              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.

              Comment


                #8
                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?

                Comment


                  #9
                  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, 12:54 AM.

                  Comment


                    #10
                    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, 09:34 AM.

                    Comment


                      #11
                      Originally posted by synchro View Post
                      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.


                      I kinda understand what you're saying and wonder if it would just be easier to install breakers that only allow either the phase converter to run(which turns on 1 of 2 possible motors), or the other motors to run if the phase converter is off. With this set up, then I'd have to install seperate motor disconnects for the motors other than the breakers as disconnects to satisfy code requirements as well. This is very confusing wether or not a 90 amp service is enough to power all of this including the branch curcuits for plugs and lights in the warehouse as well.

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