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  • Help me with these switches

    My drum thickness sander has a bad switch. This switch controls the 120v drum motor and the DC motor with a variable speed belt feeder. They are both open when off and both running when switched on. You can unplug the drum motor to adjust the tracking of the feeder belt. The bad switch is a DPST with four terminals; the switch that is shown to the right and is rated the same but it's a SPST with three terminals. Can I rewire the new (3 terminal) to work like the 4 terminal? What is the third terminal for? ground? I check the 3 terminals using a continuity checker
    Click image for larger version  Name:	IMG_7124.jpg Views:	0 Size:	9.37 MB ID:	1909560
    Last edited by Tungsten dipper; 11-09-2020, 03:41 PM.

  • #2
    I just answered my own question. I will have to order a 4 terminal switch. Just found one on Amazon (you just have to known the right words in the description to find it).
    Last edited by Tungsten dipper; 11-09-2020, 03:59 PM.

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    • #3
      grounds should never be switched and should be attached to any metal part of the assembly to bond it. Jim

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      • #4
        Occasionally you see a N terminal when the switch is illuminated.
        I just received some like those 4 terminal off Amazon.
        Max.

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        • #5
          I've taken those apart before and cleaned the contacts. They have a tendency to arc. In your case sounds like arced / stuck in the on position.

          My Shop Vac had a really cheap chicom switch that would fail in about a month. The closest replacement I could find was just as cheap as the factory original. The company got tired of sending me complete motors just for a switch because the switches weren't sold separately. Stupid them. I got three free complete motors because of that. Lucky me !

          I finally replaced the switch with a good bat handle toggle and haven't had a problem since. But it was a pain to revamp the plastic housing where the original switch was mounted and adapt it to the toggle switch.

          JL...............

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          • #6
            Hi Tungsten Dipper,

            You can use the new switch, you just have to change wiring in the equipment. The old switch, did it have 2 white wires and 2 black wires connected to the old switch? If so the white wires should get wired together and the black wires go on 2 of the 3 terminals. You should be able to read a "NO" "C" "NC" on the back of the new switch. Put the black wires on the "C" & "NO" for the equipment to operate.

            Now if the switch does not have the "NO" "C" "NC" then you will need to find continuity between 2 terminals when the switch is in the "On" position. That would be "C" & "NO" then you need to try each of the first terminals with the third terminal in the "OFF" position and you have determined the "C" & "NC". Now you hook the black wire from the power source to the "C" and the motor wire to the "NO" terminal and you have now replaced the switch.

            Disclaimer here. If you are not comfortable working with electricity DO NOT attempt this. I have only given suggestions as to how this could work you are on your own for actual installation and operation.

            TX
            Mr fixit for the family
            Chris

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            • #7
              Do I understand correctly that you want to replace the switch on the left with the one on the right?

              If the one on the left (DPST) controlled two separate motors, the 120v and the DC, then you will have to replace it with a similar switch. As a double pole switch it's two separate switches in one. It controls two separate circuits simultaneously. You can replace it with a double pole double through switch (6 pins) without center off, and just ignore the two extra pins.
              Last edited by tom_d; 11-10-2020, 08:41 PM.

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              • #8
                Originally posted by tom_d View Post
                Do I understand correctly that you want to replace the switch on the left with the one on the right?

                If the one on the left (DPST) controlled two separate motors, the 120v and the DC, then you will have to replace it with a similar switch. As a double pole switch it's two separate switches in one. It controls two separate circuits simultaneously. You can replace it with a double pole double through switch (6 pins) without center off, and just ignore the two extra pins.

                Mr Fix it and Tom,
                I found a new switch exactly like the old one so I will use that.
                Click image for larger version

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                • #9
                  And just so you're clear for next time the switches do not have the ground or neutral attached to them. All contacts on a switch normally go to the hot side. A neutral would only be used if there was a pilot light in the switch. The rest of the contacts are either directly to the hot line(s) coming in and an outgoing hot or black line which goes hot when the switch is on.

                  If you connected the black and neutral as shown in your picture the switches would simply short out the power. The motor would not turn because you didn't feed power to it.

                  The other switch with three connections is either a SPDT or it has a powered light so it would then be an SPST with neutral for the light only. The diagram or names for the connectors showing the contact format should be printed on the other side or molded into the plastic. Sometimes that molding is really sketchy and I've needed my extra power magnifier to see what I needed. But it was there.

                  Someone above may have mentioned this already and I missed it. If so then sorry for the repetition. But I didn't see anything like this.
                  Chilliwack BC, Canada

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