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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.
  6. SeaEric, Jun 15, 2025 at 10:47 AM
    #6
    SeaEric

    SeaEric YF Historian

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    I have a portable boost transformer that I deploy when needed. I bought it from Wards Marine Electric in FLL.
  7. alvareza, Jun 16, 2025 at 9:15 AM
    #7
    alvareza

    alvareza Senior Member

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    That’s interesting. I’m going to call Ward’s to see what they might have. I’m still unsure whether I need an iso-boost transformer or if an isolation only one will work.

    In parallel, I’m trying to fix any neutral to ground connections. I replaced the old Sentry battery charger with a ProMariner 1260p. It trips the shore power breaker as soon as I turn the panel charger breaker on.

    I tried checking every neutral for connectivity to ground behind the panel and found none. The main neutral to the wiring block does have connectivity to ground. The main neutral has connectivity to ground with either the generator or the shore power main breaker on. If I turn both breakers off there is no connection to ground from the neutral. I assume there should be no connection when the shore power main breaker breaker is on in the boat and the pedestal is off

    Picture shows where I was testing each neutral for connectivity to ground and found none.

    Could the surge protecter that’s seems broken be the issue?

    upload_2025-6-16_9-15-30.jpeg
  8. Pascal, Jun 16, 2025 at 9:36 AM
    #8
    Pascal

    Pascal Senior Member

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    Generators bond G to N internally but as long as you have a rotary switch or breaker that includes N, it will not be an issue.

    Most pedestal breakers only interrupt the hots, not the neutral. I would disconnect the cable to remove any doubt when testing

    not sure how the surge protector is wired but if it’s not working I would remove it just to be sure It looks like a residential unit so who knows…

    and don’t forget to unplug any major applicances like stove, fridges etc for testing.
  9. Capt Ralph, Jun 16, 2025 at 11:16 AM
    #9
    Capt Ralph

    Capt Ralph Senior Member

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    Reminds me of a good bug we had years ago.
    220Vac household laundry dryer was strapped for the old 3 pin plug (B,R,G).
    220Vac household laundry dryer uses a 115Vac timer. With no white wire, the timer was strapped to black and green. Standard household practice.

    later, on another boat we were ready; Quickly found a 220Vac household oven with 115Vac lights strapped to green. This was so intermittent to the owner it was driving him crazy.

    Humor; On both boats, when the wife was allowed to speak, she identified the bug.
    Running the laundry pops the GFI breaker. Using the oven pops the GFI breaker.
    Further, both boat wives comment, there was no problems before the husband installed the new appliances.

    When I replaced the oven on our 47 Year old Bertram a few years ago, I noticed the 220Vac, 4 pin connect. Then realized; Like that laundry dryer, this oven used 115Vac lamps and timer.

    Another friend discovered a similar bug during his installation of brand new 220Vac, Bosh laundry equipment. The fancy display and computer are 115Vac and needed the 4 pin connect (with white wire).

    So long stories finally ending; Follow brother Pascals advice and manually unplug every appliance, light, clock, TV, everything on the boat and test again.
    Further, ensure your shore/gen switch correctly disconnects the white wires from the gen-set and inverters.

    But wait, there's more; A fellow tech had a story of a new customer's mess. A previous owner had run a sub branch run from the service panel to the engine room for a new outlet and light install. With all the breakers off, the ER lights were still on AND tripping the shore GFI breaker. Never trust what your looking at.

    Be careful in those panels brother, voltmeter first before sticking your fingers in there.
    Last edited: Jun 16, 2025 at 11:44 AM