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Isolation transformers

Discussion in 'Technical Discussion' started by alvareza, Jun 12, 2025 at 10:58 AM.

  1. alvareza, Jun 12, 2025 at 10:58 AM
    #1
    alvareza

    alvareza Senior Member

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    Regarding isolation transformers. My boat has a 240v 50a shore power connection. I’m told that when connected to a 3 phase shore outlet, a boost function is needed in order for it to provide correct voltage on the 120v legs. The transformers with boost capability are much more expensive. How common are 3 phase dock outlets? What issues could arise from using a non boost isolation transformer?
  2. rtrafford, Jun 12, 2025 at 11:24 AM
    #2
    rtrafford

    rtrafford Senior Member

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    You’re likely to encounter many marinas that don’t invest in transformers that output 240 volts, but rather split off legs of 208. You’ll be starting quite low once that voltage drops as it travels under load demand.

    Highly recommend the boost. Your gear aboard will thank you, especially AC and galley.
  3. rtrafford, Jun 12, 2025 at 11:26 AM
    #3
    rtrafford

    rtrafford Senior Member

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    ….in other words, even the 50 amp outlets will be low voltage. It’s not just 3 phase plugs that will trouble you. In fact the 3 phase outlets will likely be delivering something closer to 208 than the 30’s and 50’s. Very common.
  4. Capt Ralph, Jun 12, 2025 at 11:35 AM
    #4
    Capt Ralph

    Capt Ralph Senior Member

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    Your listening to incomplete information.
    Stop doing this.

    3 phase is nothing to worry about.
    It offers a very strong 208Vac. If you look at mfg data and equipment tags, ships equipment can run on voltages below 200Vac. Most important is that the current (Amps) is there.
    3 phase 120Vac voltages are still 120Vac as always. Because of a slight shift in the alternating voltage signal (120° vs 180°), the wave form only measures 208Vac vs the normal 220Vac we usually see.

    https://en.wikipedia.org/wiki/Three-phase_electric_power

    3 phase offers lots of benefits to new installations.
    New marinas and docks, rebuilt marinas and docks even existing marinas and docks are updating to 3 phase services.
    When you notice big transformers on or around a dock, Those are probably the 3 phase Wye transformers rite before your boats dock service pole.
    You probably have already used 3 phase and never knew it.
    In a short more time, probably all docks will be powered this way as utility and codes change.

    Please keep in mind; Nothing is free...
    Boost transformers can make a taller voltage level but it cost current (Amps) to do so.
    It takes amps to start compressors not volts.
    Kind of sounds counter productive, uh? It can be..

    Relax, keep your shore power connects dry and clean.
    Get off the docks more. :)
  5. YachtForums, Jun 12, 2025 at 1:07 PM
    #5
    YachtForums

    YachtForums Administrator

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    This thread is being split into a new discussion as requested by senior members following a post unrelated to the previous topic.