Old Okamoto Grinder 3Phase Switches
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  1. #1
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    Default Old Okamoto Grinder 3Phase Switches

    I am restoring this Okamoto OMA 350. I got it with the wiring removed. I have the manual with the wiring diagram and new normally open/normally closed push buttons.
    However, I see no motor contactors for switching the three phase for the grinding wheel or the dust extractor. Nothing shows up on the wiring diagram... What am I missing???

    okamoto.jpg

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    It appears you are missing the contactor!

    Welcome to the forum.

    Stuart

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    There must be a more detailed schematic somewhere. Each motor requires a start contactor and a heater for thermal protection.

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    Quote Originally Posted by ewlsey View Post
    There must be a more detailed schematic somewhere. Each motor requires a start contactor and a heater for thermal protection.

    Not necessarily.

    If the motor is under 1 HP, it can use a built-in thermal. The blower may be well under that.

    If you look, the "switch" is actually a "manual motor starter", with overload protector. The additional motor etc can run from that line if motors are considerably smaller, and have their own internal overload.

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    OK. I've never seen a 3 phase motor with internal thermal protection. But, I guess I have not studied small 3 phase motors.

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    My 5hp 3 phase Marathon motor has a built in thermo switch. Set to be in series with LV contactor wiring, in this case wired to the VFD.

    The diagram shows a manual push button contactor with heaters, No primary wiring. I had a Harig grinder wired the same way. I use the same on my air compressor, toggle 3phase switch with heaters. These type components are pricey new, ebay is where I buy that stuff. Often find NOS for fraction of new.

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    Quote Originally Posted by ewlsey View Post
    OK. I've never seen a 3 phase motor with internal thermal protection. But, I guess I have not studied small 3 phase motors.


    I have a 1 HP of that type. Therm-O-Disc overload in the wye point, easy, cheap..

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    O.K.

    I contacted Okamoto Service in Illinois and this is what they said

    "This is only a 200 v machine and does not use a contactor , power goes through the switch’s as it shows in the diagram."

    I still don't get it... What does the forum think... Ever seen 3 Phase motors set up like this? If it's not clear, the push buttons are NOT ganged together.

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    It is a manual motor starter. Just like a contactor except you push the button. Provides overload etc. It's just how it works.... basically an "on" button to run it, no drama. Perfectly fine for that type machine.

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    Default 3 Phase Manual Motor Starter

    Here is a couple examples of an enclosed manual 3Φ motor starters. Similar to what your drawing shows.

    3 Pole maintained contactor on the top and a 3 pole overload relay on the bottom.

    The one in your drawing shows no overload relay section, as these examples do. Therefore your motors should contain their own thermal overload switch internally.

    Square D 251 MCG3 Pushbutton Manual Motor Starter 1HP, 6VAC, 25VDC, 3-Pole | eBay



    Allen Bradley Manual Motor Starter | eBay



    And here's a manual operated, HP rated 3 pole, snap switch, that has no overload relay section.

    Leviton MS33-DS 3 Amp 6 Volt, Three-Pole, Three Phase AC Motor Starter, Suitable as Motor Disconnect, Toggle, Industrial Grade, Non-Grounding, Black - Wall Light Switches - Amazon.com



    SAF Ω

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    You are correct..... I did not look closely at the pic.... that's a stop button shown..... when I looked at the pic, I saw it as being the overload symbol..... Woops......

    Yes, that explains the multi motors... they all have to have their own overloads.


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