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Motor switch ideas?

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  • Motor switch ideas?

    I am making a small machine for a customer to use at shows that he goes to. He flies to shows around the country, usually in hotels, and uses this machine.

    The machine has a little 110v motor. 2 black leads for the power and a green one for the ground.

    The big and bulky machine he has now has a larger motor and from the pictures I see, the ground wire is simply screwed to the aluminum base of the machine. The on/off switch to the motor is also on the power cord.

    I thought, no problem, I just find a in-line power switch with a ground connection, wire it up, even and idiot like me can do this. So naturally, I can not find a in-line power switch with a ground.

    I don't know that the ground wire being attached to the aluminum base is a good idea or a bad one. I do know that the base sits on a folding table that hotels have with a table cloth, so the base isn't grounded to anything.

    Is it safe to just attach the ground wire to the base like that? Is there a reason why there isn't a inline power switch with a ground? Do I need to put a little junction/wiring box with a ground on the machine?

    Ideal situation is an inline power switch that's safe. Safety is the priority. If I can avoid the space and weight that a junction box adds, I would like to do so. Goal is to minimize space and weight of the machine so that it fits into a suitcase that goes on a airplane.

    I don't know if his current setup is unsafe, and what I need to do to make my machine safer, while at the same time minimizing space and weight.

    Any suggestions or ideas?

  • #2
    Why does the switch need a ground? Just let the neutral and ground wires pass the switch and switch the hot lead. All you need is room in the switch for the wires.


    • #3
      If the machine/motor frame ground just goes to the frame but is not connected to the socket ground it is dangerous.
      Can you not fit a switch on the machine itself and feed it with a three conductor cord?
      If it is a small motor, just a simple SPST switch rated for 240v will be good enough?
      Inline switches are usually designed for simple two wire devices.
      If you must have the switch external to the machine, make up a short 3 wire cord with a switched receptacle on the end and plug the unit into that with a three pin plug?
      Last edited by MaxHeadRoom; 04-18-2011, 04:21 PM.


      • #4
        Normally the ground wire passes through the in-line switch without making any connection there. It doesn't need to. It does need to connect the housing of the powered equipment to the plug ground pin.

        They still make those in-line switches- I saw one at Rona the other day.
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


        • #5
          Inline switches of the kind that were used on standard lamps are not much good for anything else as they have absolutely minimum isolation and if used on an inductive load, a motor for example, they are prone to arching over. Not what you want to happen when you are holding it in your hand!


          • #6
            Use a power bar and switch there.
            Free software for calculating bolt circles and similar: Click Here


            • #7
              project box

              You could use a small project box from Radio Shack, power cord goes into the box, hooks to the switch or other control, comes out of the box to the machine. Also, the ground wire is not normally switched, the ground should be connected to the machine no matter what position the switch is in.


              • #8
                If its 110, it doesn't need a separate ground, neutral and ground are tied back at the breaker box. Just switch the hot.
                James Kilroy


                • #9
                  Originally posted by jkilroy
                  If its 110, it doesn't need a separate ground, neutral and ground are tied back at the breaker box. Just switch the hot.
                  Great way to get killed, I sure do hope you are not an electrician.


                  You guys have those polarised mains outlets, right? In here we have unpolarised, so every mains switch has to have two poles so it cuts off both leads (live and neutral), as they can be switched by turning tthe plug around.

                  BUT you will never ever ever put a switch in a ground wire!
                  Amount of experience is in direct proportion to the value of broken equipment.


                  • #10
                    [QUOTE=baldysm]the ground wire is simply screwed to the aluminum base of the machine. The on/off switch to the motor is also on the power cord./QUOTE]

                    I am assuming you are in US and we are talking about a 3 wire cord, green conductor ground, white neutral, and black hot, and that a "small" motor is a fractional horsepower one running on 110 volts. I am also expecting that the only thing the cord connects to on the machine is the motor.

                    Just switch the black wire. Change the connection on the green wire to the motor itself and not the aluminum base. Any motor vibration insulators could be an electrical insulator as well and you want to protect against any motor electrical faults. The switch on the black wire should be rated for the inrush current to the motor, which is higher than the operating current. Most switches these days have a horsepower rating on them, but a 15 amp switch is easy to find and inexpensive these days and should work indefinitely with up to a 3/4 horse motor. Inline or mounted is your choice, but if inline, make sure the switch will contain all three wires plus the outer insulation. Properly wired, an inline switch of the proper rating (and that will eliminate the light duty thumbwheel type) will be sufficiently insulated by the plastic casing of the switch, but I question whether the strain relief is adequate for abuse that comes with lots of travel, set up, and take down, and you do not want the insulation to pull out of the switch. I would lean toward a junction box or chassis box with a good strain relief clamp, and if metal, I'd connect the ground wire to it too.