Correct wiring, three phase motor
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  1. #1
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    Default Correct wiring, three phase motor

    Apologies if this question is misplaced, but I am sure several people here know the answer.

    I've have a Swiss 3-phase 1/2 HP 50Hz motor from the 1960s, marked 380/220V on the nameplate. I believe that it's currently set up for 380V 3-phase but wanted to confirm that.

    - In the connection box is a label which (translated from German) reads: "Attention: for star connection the star point of the motor windings is behind the connection box."

    - In the connection box, the three phase supply is attached to three motor wires labeled U, V, W.

    - Behind the connection box are three more motor wires labeled X, Y, Y that are all tied together with a blue crimp connector. I suppose that this is the "star point" of the motor windings as per the label.

    Could someone here please confirm that the way it is now wired, with supply connections to U, V, W is indeed the 380V three-phase variant? Or if not, advise me on how to reconnect the wires?

    Cheers,
    Bruce

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    Use the diagram on the right, your labels may be slightly different.

    https://dealersindustrialblogdotcom....ead1.jpg?w=648

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    The motor is 220/380. Those voltages are when wired delta and star, respectively. As a sanity check, windings wired star are always a higher line-to-line voltage than the same windings in delta, and 3 phase is always given with the line-to-line volts unless otherwise stated.

    Your motor has a star point, so it is wired star.

    So, yes you should be set up for 380, assuming the motor is not rewound, etc, and is still as per the name tag.

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    Dear JST,

    Quote Originally Posted by JST View Post
    The motor is 220/380. Those voltages are when wired delta and star, respectively. Your motor has a star point, so it is wired star.
    This makes sense. I've looked at these wiring diagrams

    and that also agrees. The blue crimp connector where the three motor wires are tied together can only be the central (star) point labeled "n" on the left side of the diagram. So as you write, it is currently wired for the the higher voltage 380V variant.

    I have a further question about this. My three phase power is over five wires: L1, L2, L3, neutral and ground. It is clear where the L1, L2, L3 and ground connections should be made (the terminal box has a grounding point which is the motor frame). Do you know if I should leave the neutral disconnected? Or should I connect the neutral to the star point? Suppose that I want to put a three-phase ground-fault interruptor upstream?

    Cheers,
    Bruce

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    Neutral needs to be disconnected
    The neutral is in the powerline to get 220volts single phase (Neutral and one Phase)
    Eighter for the controle circuit or a light or a DRO for example
    In the past you had plenty of 3 phase wall sockets without neutral

    Peter

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    You do not need to connect the neutral, whether or not it has ground-fault protection.

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    In fact, you SHOULD NOT connect it. It does not help on motors, and can cause unbalanced currents.

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    Last post in this thread. Connected motor to 380V 3-phase today. Runs perfectly. Now need to decide if I want to put a VFD on it or just a protection relay.

    JST, Peter, thanks for answering my questions!

    Cheers,
    Bruce

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    If it has a controle circuit I would place a correct sized overload relay in front of the contactor
    If it does not have a controle circuit I would use a motor protection circuit breaker with a emergency stop and device for disconnecting if without power ,all in one small enclosure

    Peter

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    Quote Originally Posted by Peter from Holland View Post
    Neutral needs to be disconnected
    The neutral is in the powerline to get 220volts single phase (Neutral and one Phase)
    Eighter for the controle circuit or a light or a DRO for example
    In the past you had plenty of 3 phase wall sockets without neutral

    Peter
    In the past, in Switzerland at least, it was common to have no neutral and to bond ground and neutral. My first workshop was bonded at the panel (think asbestos panel with fuse blocks spattered all over it); a contractor friend told me that was accepted back in the day. Second shop had neutral... current shop has neutral and ground fault protection. Pretty quickly figured out which machines had four wire cabling when I turned on their lamps!

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    Quote Originally Posted by Screwmachine View Post
    In the past, in Switzerland at least, it was common to have no neutral and to bond ground and neutral. My first workshop was bonded at the panel (think asbestos panel with fuse blocks spattered all over it); a contractor friend told me that was accepted back in the day. Second shop had neutral... current shop has neutral and ground fault protection. Pretty quickly figured out which machines had four wire cabling when I turned on their lamps!

    Your ground fault circuit interrupter will trip inmediatly when you use the ground as neutral
    I sometimes have a machine where the ground is used randomly to generate 220volts single phase
    You have to figure out where it is connected to ground then That can be challeging sometimes

    Peter


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