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Thread: Unusual Use for an MTS?

  1. #1
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    Unusual Use for an MTS?

    An existing 100 amp load is supplied by a 3-phase 100 amp breaker. A new 100 amp load is being installed. The system can't handle the load of both the existing and the new at the same time, and there will never be a need to run them both at the same time. What do you think about using a Manual Transfer Switch to select which load will get power and be allowed to operate?
    Charles E. Beck, P.E., Seattle
    Comments based on 2017 NEC unless otherwise noted.

  2. #2
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    Quote Originally Posted by charlie b View Post
    An existing 100 amp load is supplied by a 3-phase 100 amp breaker. A new 100 amp load is being installed. The system can't handle the load of both the existing and the new at the same time, and there will never be a need to run them both at the same time. What do you think about using a Manual Transfer Switch to select which load will get power and be allowed to operate?
    sounds workable to me
    Bob

  3. #3
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    Not at all an unusual application for it. Done all the time.
    __________________________________________________ ____________________________
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  4. #4
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    Keep in mind if there if any type controller such as a motor starter/contactor is involved you might accomplish the same thing by use of a selector switch in the control circuits.
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

  5. #5
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    Might be able to be accomplished with a breaker interlock device. Those are sometimes used for residential generator interlock purposes.
    Don, Illinois
    Ego is the anesthesia that deadens the pain of stupidity. Dr. Rick Rigsby
    (All code citations are 2017 unless otherwise noted)

  6. #6
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    We have done this several times as well. Works just like 3-pole, 3-way switch.
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

  7. #7
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    I haven't visited the site yet. I may be able to do that next week. There is a question of whether the panel has room for an additional 100 amp breaker. So the thought is to intercept the existing branch circuit from the panel's 100 amp breaker (serving an electric unit heater), insert the MTS, and run the other side of the MTS to the new 100 amp load (a heat pump). Sounds like it is a viable option. Thanks for the comments.
    Charles E. Beck, P.E., Seattle
    Comments based on 2017 NEC unless otherwise noted.

  8. #8
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    Quote Originally Posted by charlie b View Post
    I haven't visited the site yet. I may be able to do that next week. There is a question of whether the panel has room for an additional 100 amp breaker. So the thought is to intercept the existing branch circuit from the panel's 100 amp breaker (serving an electric unit heater), insert the MTS, and run the other side of the MTS to the new 100 amp load (a heat pump). Sounds like it is a viable option. Thanks for the comments.
    Funny that you've mentioned a unit heater, we recently had a room that stored the building window washing unit that they wanted to heat during the winter. Since getting a new circuit there was nearly impossible we intercepted the washer circuit and installed a 100 amp MTS. During the winter months when the window washer isn't used the building engineer switches from washer to unit heater.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

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