Use a 3 pole reversing contactor for 1-phase 220?
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  1. #1
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    Default Use a 3 pole reversing contactor for 1-phase 220?

    I have a lathe that I am converting from 3 phase 220 to single phase 220.

    I would like to reuse the reversing contactor/pushbutton setup.

    For forward>>reverse, the contactor internally switches L1 & L3, while L2 is always straight thru.

    My single phase motor uses L2>>P1 L1>>T4-T5 and T2-T3-T8 for CCW and
    L2>>P1 L1>>T4-T8 and T2-T3-T5 for CW

    Problem I see is that I need another pole to switch T4, which I don't have.
    The manufacturer's tech support briefly told me this would work on single phase, but I don't see how at this point.

    Am I missing something, or are drum switches the only viable option for reversing single phase motors?

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    No auxilliary contacts?

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    hmmm... i seem to have drawn a picture that does it with your three contactor......

    let me scan it in and attach when I wake up.

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    this work? (hope its readable - from phone camera)

    bottom line is put T5 thru 1 contactor set and T8 thru another and L1 thru 3rd

    scanned and pix replaced so can read

    wouldn't this work?
    Attached Thumbnails Attached Thumbnails 3ph.jpg  

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    Mike,

    One problem I see with your drawing is that L2 constantly supplies power to the motor.

    With my playing around with this, I seem to reach a point where I need an extra pole to make/break L1 to T4 in forward & reverse.

    My contactor does not have an aux contact, but I am thinking I need to add one, or I can add an external definite purpose single pole contactor, to make/break L1 to T4. Bring the 220v coil voltage from the main contactor over to the small contactor. Grainger sells small compact contactors with a 220v coil for $20.

    I will attach the motor wiring, contactor wiring, and my drawing in the next post.

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    why is L2 always connected a problem? I often use a single contact for a motor rather than break both sides of it.

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    See attached motor wiring diagram, control wiring diagram, and my diagram, in PDF.
    Attached Files Attached Files

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    Quote Originally Posted by mike_kilroy View Post
    why is L2 always connected a problem? I often use a single contact for a motor rather than break both sides of it.
    When a motor is switched off it should be totally de-energized. Being single phase 220 L2 still carries 120v to the windings.

    In a single phase 110 device, it might be ok to break the live pole and leave the neutral connected.

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    Hi Tony Having one side hot is very common. It's not the best thing to do but it's done often. Look at post "can my 3 phase comp.be wired for household 220V" It will show a 2 pole pressure switch that was connected at the factory to a 3 phase motor. I've seen it done that way many times. It is not a problem that one side is hot! Be very stupid for anyone to work on a compressor connected to a pressure switch!!
    Yes if you worked on the motor one side will be hot to ground but no one in their right mind will work on a motor connected to an electronic controlled switch! Even in OSHA lock Out Tag Out an electronic switch can NOT be locked out and comply with the regulation. If there is a plug it can be pulled and locked in a container, A breaker can be locked in the Off position and a Manual disconnect can be locked in the open position.
    So wire one line direct and use the 3 contacts on each contactor to get forward and reverse. Be sure you make provisions that nothing will happen if the Forward and reverse button is pushed at the same time or when the motor is running in one direction pushing the opposite. I see no locking aux contacts mentioned, is this a mechanical switch?
    Frank

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    This is a reversing magnetic 3 pole contactor/starter with 220v coil. It currently has no aux contacts, but I may add one if necessary.

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    I assume you have push buttons? Or are they switches. What keeps the contactor energized?
    Frank

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    Quote Originally Posted by Froneck View Post
    I assume you have push buttons? Or are they switches. What keeps the contactor energized?
    Frank
    momentary pushbuttons, if your interested in how the coil stays energized look at the at the previously attached wiring diagram. But my issue is not with controlling the coil. I am looking to energize/de energize a single phase motor with a 3 pole switch. It seems to me that I need an aux contact for a 4th pole, unless I am missing something. And leaving one motor winding with constant power is poor design, and probably against some electrical code.

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    The typical 'auxiliary contact' that piggy backs onto a mag isn't HP rated and isn't intended for motor load, it's a control circuit item.

    If a person wanted four poles he would purchase a four pole contactor.

    Stuart

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    Quote Originally Posted by atomarc View Post
    The typical 'auxiliary contact' that piggy backs onto a mag isn't HP rated and isn't intended for motor load, it's a control circuit item.

    Stuart
    Yeah you might be right about that, the aux contact is for control circuit use.

    Reversing magnetic contactors in 4 pole don't seem to be very common, at least not listed in Grainger.

    I will probably follow my original plan to add a single pole compact contactor with 220v coil, wire the coil in parallel with the 3 pole contactor coil, and use it to make & break L1 >>T4 with it. Only $20 from grainger.

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    Hi Stuart
    Looking at the diagram of the reversing switch you do have AUX Contacts. I was asking because AUX contacts are needed to allow push buttons to control the contactors. When FWD button is pushed it connects the coil to the line, closing the 3 main contacts and 2 Aux. One (shown below the FWD contact) is used to keep the coil energized when the button is released. It also opens 1 closed contact that is connected to the R button so it does not have power if pushed while the F contactor is closed. If you have the Reversing contactor in the drawing you do have an extra Normally open contact and it is used in the wiring diagram in the next drawing you supplied.
    Frank

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    While I was typing I see the other posts. Your motor load is not going thru the aux contacts. T5 and T8 is your start winding, start Capacitor and run Capicitor. It will draw very little current. All the windings are protected by the thermal switch P1. Do you have the ratings for the contactor?
    Frank

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    The contactor is a NEMA 00, which is 9 amps per pole. I don't see a rating for aux contacts, but I see Square D rates theirs around 5 amps.

    I don't think my contactor has a aux contact, it's attached as an add-on, but you can take a look at the picture.
    Attached Thumbnails Attached Thumbnails imag0082.jpg  

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    Having no disconnect for one of the incoming hot lines for a 240 volt single phase
    motor is really not the best approach to life.

    One dodge around this works when the start winding for a dual voltage motor
    has one end rigged to the center-tap of the run winding. This is actually a pretty
    common feature.

    If this is the case, then one can use two poles on a three pole disconnect or drum
    switch to provide the incoming 240 volt line. This leaves only one pole to
    reverse the start winding - sounds impossible, right?

    Here's how it's done:



    In this case the middle pole ties one end of the start circuit to either L1 or L2.
    Because the other end of the start circuit is tied to the centertap on the run
    winding, it effectively swaps the current direction in the start winding.

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    He has a reversing contactor Jim. I did mention not switching one line. The drawing he provided shows Aux contacts but I don't see them in the photo. His motor is similar to the one you show except the start switch is connected to the start Cap and allows current to flow thru the run cap. and start winding when the motor is up to speed.
    Tony What are the Amps of the motor? You have a 9Amp contactor that was connected to a 3 Phase motor, those heaters might be too small. You can do like Jim said but use your contactor if you don't switch one side of the line.

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    Hi Tony,

    Use Jim's approach: Only with the drum switch in the up position is one contactor energized. And the lower position is the other contactor energized. Both sides of the line are switched.


    White on Jim's drawing is P1 on the motor
    White 2 is your T5 lead on the motor.
    White 3 is not used
    White 4 is your T4 lead.

    If you can get to the T1 lead to use instead of the P1 would be very helpful, since it would be possible to (with the thermostat tripped) to get a funny skipping motion only in one direction. Use the proper "heaters" in the starter you use, and you won't need the thermostat in the motor.

    Do a "reality" check on the motor nameplate current and your starter full load current.
    You probably will need one or two sizes larger starter to handle the current.

    Bill


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