3-phase drum switch for 1-phase motor
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  1. #1
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    Default 3-phase drum switch for 1-phase motor

    Hello,

    I have a lathe that I am currently replacing the motor from 3-phase to 1-phase but since the current drum switch (AB with 6-contacts) is already installed, can it be used for a 1-phase motor? The motor is 1hp.

    Thanks,
    Shaffin.

    img_20190216_124828.jpgimg_20190216_124802.jpgimg_20190216_124953.jpgimg_20190216_124753.jpgimg_20190216_124859.jpg

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    You can use a 3 phase drum switch on single phase, I've done it many times. You will have to determine how the single phase motor is connected for reversal. Some can not be reversed but I'm thinking you will be using one that will. Heaters on the contactor will have to be changed if using a motor with same HP. They will be too small. Also understand you will not be able to reverse the spindle like you did with 3 phase, you will need to wait until the centrifugal switch reconnects the start winding. Reversing the drum switch sooner will result in the motor continuing the same rotation.

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    Yes indeed.
    Now I'm not familiar with canadian practice so think you should ask a knowledgeable local person to help you out.
    Basically you should think of your 2 current carrying leads (live and neutral) as two out of your three phase leads - disconnect the third, which you don't need.

    And by all means,do connect the protective earth lead!

    If you can post diagrams, surely somebody will chime in.
    Regards, fusker

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    No! You can not connect a single phase motor as a 3 phase motor with only 2 wires. Reversing the wires on single phase motor will not reverse rotation. Most of the drum switches for 3 phase will disconnect all 3 wires from the motor, only 2 will reverse the wires the other simply acts as an on off on switch. Also remember the ground wire is not a neutral, neutral is current carrying the ground wire must not carry current though both are connected to the same place in the breaker box. Single phase motors have a 120VAC start winding if they are dual voltage. The junction to form 240VAC series is used to obtain 120VAC when used with 240VAV.I'm sure there are motors that operate in other ways but that is what I seen to be most common. The cover or possibly the name plate will have the schematic to reverse direction.

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    I found the original schematic attached!

    Attachment 250422
    Attached Thumbnails Attached Thumbnails schematics.jpg  

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    That schematic is for the original 3 phase motor. You will need the wiring diagram for your single phase motor. As I said you have the typical 3 phase drum switch, 2 set of contacts that will reverse the input to output and one is on-off-on like I mentioned.

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    If you aren't confused enough already you can reverse the direction of a non-reversible single phase motor by switching out the start and run capacitors for inductors. It's not recommended or easy to do properly, but it can be done.


    To actually answer your question count the leads on that drum switch. If it has six going in and three going out it is a 3pdt switch and can control the direction of any reversible single phase motor. If the switch has fewer terminals it's probably still doable but I can't say for sure without seeing the other side of the switch. I want to say the minimum is dpdt, but there is an exception to that even.

    So almost certainly yes. Do you already have the motor picked out? If so snap a picture of the nameplate.

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    Quote Originally Posted by Froneck View Post
    You can use a 3 phase drum switch on single phase, I've done it many times. You will have to determine how the single phase motor is connected for reversal. Some can not be reversed but I'm thinking you will be using one that will. Heaters on the contactor will have to be changed if using a motor with same HP. They will be too small. Also understand you will not be able to reverse the spindle like you did with 3 phase, you will need to wait until the centrifugal switch reconnects the start winding. Reversing the drum switch sooner will result in the motor continuing the same rotation.
    Capacitor run motors will change direction if you plug reverse them, but the only ones I've tried were adjustable speed type and I'm really not even sure how those run well so far below synchronous speed.

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    Not all Single phase motors are reversible, shaded pole motors will not reverse. Capacitor start motors will reverse by changing the capacitor phase connection. Some motors don't have that option but doable if someone whats to rewire rather than use provided terminals, the same with plugging to slow the motor below the speed of the centrifugal switch. If the motor is of the Run/Start capacitor type it is much easier but either type get a little more complicated than using a drum switch.


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