50amp/220V reverse polarity

Discussion in 'OnBoard Electronics & Controls' started by Larry Hayden, Feb 17, 2009.

  1. Larry Hayden
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    Larry Hayden New Member

    I just purchased a Silverton 39 with 50 amp / 220 V service. It does not have a reverse polarity indicator. I asked the Silverton dealer and they said that 220v systems do not need to worry about reverse polarity. Regardless--the marina says I have got to have an indicator. Has anyone solved this problem? Can I get an inexpensive polarity indicator for 50amp/220v system?
     
  2. pistnbroke
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    pistnbroke I try

    with the american 220v system you have a central earth with each cable 110v above earth . I think you need to get clarification from the Marina what they want you to fit as your dealer might be right
     
  3. robherc
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    robherc Designer/Hobbyist

    As much as I disagree with pistnbroke on MANY of his statements....he's dead-on right this time (well, at least where US HOME wiring is concerned).

    There are, unfortunately, multiple systems in use in the US now. SOME US "3-phase" systems use 3 110v phases (transfer boxes labeled "400 volts"), while others use 3 220v phases (transfer boxes labeled "700 volts").

    In the commercial/industrial applications (700 volts) each phase is 220 volts above neutral/ground; thus you can have true 220v single-phase, and consequently have actual "polarity" in your 220v setup.

    In the home applications (and the "400 volts" 3-phase ones...somewhat rare) your 220v power is actually 2-phase power with 110v per phase. In THAT application, there is no "polarity" because both leads are "hot" or "live" leads, there is no neutral/ground.


    End result, like pistnbroke said, you need to get clarification from the marina; if they're using a single-phase 220v system & you "plug-in" with your polarities switched, you could cause a short, or other wiring problems...not very likely if your Silverton 39 was made for use with "household" 2-phase 220, but if it was made for the single-phase 220, they may have "cheated" and used the "neutral" for a ground wire somewhere...and that spells DANGER if you get the polarity switched (don't you love how we over-complicate EVERYTHING in the US???).
     
  4. Landlubber
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    Landlubber Senior Member

    pistnbroke,

    Do you know brand names for Auto reverse polarity systems here mate?
     
  5. pistnbroke
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    pistnbroke I try

    Thanks robherc for that ....the object of the exercise is to get the earth on the boat to match the earth of the shore supply .....the first soldier killed in the fauklands war with argentina stepped of the ladder of a generator and when one foot tuched the ground he was electrocuted..similarly the British Narrow boats I worked on could kill you when you had one step on the boat and one on the towpath.....

    As for brands get one approved by the marina ....
     
  6. alan white
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    alan white Senior Member

    Presumedly, a 240 volt cable from a marina would have two hot lines (red and black), a white neutral line (grounded at the marina into the same earth that is under the boat), and a bare (or green) copper ground wire.
    The white wire allows 120 volt capability. In the case of 120 volts only being available, there certainly would be an issue with polarity. A simple polarity test would require only a length of wire back to the marina, where it would be grounded to a convenient outlet. Then a test for voltage would indicate either 120 volts or no voltage upon which a double check would indicate continuity (ground to ground).
    This test can be done with all of the wires in a 240 volt system, where neutral and ground should show continuity with the test wire, and the two remaining wires (usually black and red) should each show 120 volts or so when the other probe is clipped to the test wire.
     
  7. Guest62110524

    Guest62110524 Previous Member

    does Bob Abbott know youa re using his pic here:).
     
  8. robherc
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    robherc Designer/Hobbyist

    A very good description of 4-wire 220v systems Alan, thanks for adding that clarity here. (afraid I might have muddled it a bit in my description)
     
  9. TedZ
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    TedZ Junior Member

    In the US world of industrial and commercial wiring the NEC has made it easier to recognize supply power. Common three phase voltages are 208, 230 and 460...550 in Canada. Single phase voltages are 120 and 240. A polarity indicator on a 240 single phase system warns of a crossed hot and neutral which will fry equipment, could harm you and will electrify a metal dock, hand rails etc. Naturally, they would want this.

    When you see 220 VAC or 110 VAC you are simply seeing folk who are using up their old placards or are not up to speed on labeling.

    BTW one phase of a three phase system is the stated voltage divided by the square root of three. There is no such thing as three phase 700 volts that gives anything usable per phase in our world. 208 is designed to be 230 minus 10% + one volt on the theory that the motor manufacturers gave you a 10% tolerance on input voltage. 208 divided by the square root of three is 120 VAC.

    Told you all i know. :--)

    Ted
     
  10. TeddyDiver
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    TeddyDiver Gollywobbler

    I allways wondered where Enron bookies studied their math :p
     
  11. robherc
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    robherc Designer/Hobbyist

    TedZ-

    If you go back and read closer...I never stated that ANY system had an ACTUAL voltage of 700...just a warning label stating 700V...check again (and if you wish to argue that, may I suggest that you drive to the three nearest gas stations [outside city limits] and read the warning signs on their power box).
     
  12. Larry Hayden
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    Larry Hayden New Member

    My understandings of these messages are: 1) find out if the marina has single phase or 2-phase 240V system; and 2) if the Silverton was rigged similar to household 2-phase 240V system. In the end, if I have to get a polarity indicator, is there a gadget off the shelf that is inexpensive--or where should I go to find one? Thanks to everyone for the time on this. As a new boater, I learned alot.
     
  13. TedZ
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    TedZ Junior Member

    Robherc

    Your knowlege base is yours and i respect it. If you are encountering circuits that are labeled one thing but contain something else i would suggest you take a picture and send it to your County folk. Post it here while you are at it. That obviously is very, very dangerous.

    Two phase power?? I understand folks might eroneously call 240 VAC single phase "two phase" because of the two hot legs but you really shouldn't do it.

    http://en.wikipedia.org/wiki/Two_phase

    Does a good job of explaining it.

    Three phase power with 110 volts per phase sounds like 4 wire 208 which is three phase with 120 volts per phase. Three phase 400 VAC gives you nothing usable and does not exist to the best of my knowlege. 460 three phase gives 277 VAC on each leg and there is commercial lighting designed for that voltage.

    Tell me what you folks want. I'm an EE and have done commercial/industrial wiring all of my life. If you want to post stuff that is misleading and you don't want me to say anything, i obviously won't talk if this type of feedback is not wanted.

    Ted
     
  14. robherc
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    robherc Designer/Hobbyist

    Yes, I was referring to 240VAC split-phase as "two-phase" for ease of explanation. The point of my labeling it as such was to illustrate the difference between 1 "hot" and 2 "hot" lead 220 wiring; but I digress, you're right, it's not technically named "2-phase".
     

  15. alan white
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    alan white Senior Member

    Rest assured, any power supplied by a marina will be single (split) phase, and either 120 V or 240 V or both. Larger boatyards would have 3 phase power available for various reasons such as would involve large vessels, but that is an entirely different requirement.
    The marina itself may, and likely does use 3 phase power itself, but not for supplying to small pleasure boats.
    This means typical house current like at home. It means there's little to be concerned with if the boat system has been labelled properly by the manufacturer and ground fault interrupter device(s) are installed.
    In any damp location in or outside of a home, and even some dry areas such as bedrooms (and some codes require ALL circuits) to be GFI protected.
    This is good protection aboard a boat that sits in the water.
    I would always recommend any supply to a boat to have GFI protection, and I don't know if marinas are required to run their supply power through GFI devices located at the marina's panel.
    In any case, The dock outlet will (or should be) properly set up to take a boat cable, and the boat itself ought to have a similar hook-up at the other end.
    Polarity shouldn't come into question except where older or jury-rigged boats are concerned. This may be the marina's concern, but any new boat and most old boats will hook up without any fears of electricution.
    In a home, it's possible to hook up 120 V backwards and you'd never know it. Or, you might accidentally touch the threads of a light fixture and get a shock (with correct polarity, the button on the bottom of the light socket is hot, not the threads. But on a boat, reverse polarity can kill.
    This is why GFIs should be present even if the marina should have them (you never know), and why it's doubly important to test polarity at least once when a boat's new (to you) to ensure the polarity is correct.
    To do this, view the typical grounded outlet onboard as a face with two slots for eyes and a single d-shaped ground prong hole for a mouth.
    Viewed this way (with "eyes" correctly located above the ground hole), a 120 V outlet will show continuity between the ground hole and the left side. Now test for voltage between the right slot and the left slot, you should read 120 V on the meter. Now with one test lead in the ground hole and the other in the right slot, there should be 120 V.
    If there is voltage between the LEFT slot (mouth down) and the ground, the polarity is reversed.
    That should be all you need to do, and while it's a good idea to test an older more "worked on" boat, it would be really unusual for a new boat to be so fundamentally wrongly wired (but you wouldn't know without testing, would you?).
    Most any 240 V equipment onboard (AC, etc) should be hard-wired. Mix wires up with 240 V stuff and it simply won't work.
     
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