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Re: T&T: Debugging an electrical problem

From: Larry N. Brown (no email)
Date: Mon Jul 02 2007 - 08:10:15 EDT

  • Next message: Greg Bradley: "Re: T&T: Debugging an electrical problem"

    Excellent guide. I downloaded it for future reference.

    Regards,

    Larry and Teri
    M/V Cigano, 47' Prairie Sundeck Cruiser
    Lying: Slidell, LA
    N 30 13.28
    W 89 48.63

    ----- Original Message -----
    From: "Sean Welsh" <slwelsh+>
    To: <>
    Sent: Monday, July 02, 2007 1:08 AM
    Subject: Re: T&T: Debugging an electrical problem

    > Greg Bradley wrote:
    >> We we are on shore power (50A), ... The electric stove will sort of
    >> power on, but the
    >> burners never get very hot and the LED "On" light does not light.
    > You don't mention it explicitly, but I assume your 50A shore connection
    > is actually 50A, 240V. If so, it will have three slots/blades and a
    > ground tang on the outer circumference of the connector.
    >
    > I am guessing (wildly) from the description of your symptoms that you
    > also have a 240-volt stove. I am further guessing that, up to now, all
    > the 50A shore services you have used have been full, 50A/240V/120V
    > services.
    >
    > I think your current problem is that the shore receptacle you are using
    > is either (1) completely wrong, inasmuch as the two "hot" legs of the
    > service are both connected to the same "phase" or "leg" of the shore
    > power system. In this case, you would have only 120VAC available on
    > your boat, and 240-volt appliances would see zero volts (240-volt stoves
    > are sometimes wired so that you will end up, in this sort of
    > circumstance, getting half voltage, or quarter power, at the burners),
    > while all your 120-volt appliances would work normally. This is a
    > dangerous condition, because you may well be returning much more than 50
    > amps on the neutral wire, which is only rated for 50 amps.
    >
    > Or (2), the two hot legs of your power source are actually derived from
    > two out of three of the phases of a three-phase supply. In which case,
    > your phase-to-neutral voltage will be 120 volts, and thus all your 120
    > volt appliances will work fine, but your hot-to-hot voltage will be 208
    > volts instead of 240 volts. Depending on the model of stove, that may
    > be just enough too low for the stove to exhibit the described symptoms.
    >
    > Get out your voltmeter and measure between each hot leg and neutral, and
    > then measure between the two hot legs. If you get 120 hot-to-neutral,
    > and 0 hot-to-hot, you have condition (1), if you get 208 hot-to-hot you
    > have condition (2). (You can figure out where on the receptacle to
    > measure from this guide:
    > http://www.marinco.com/docs/guides/Boater%27sGuidetoACElectrical.pdf --
    > figure 4 on page 5. W is neutral, and X and Y are the two hots.) If
    > you get different readings than these (such as normal readings of 120
    > and 240, respectively), then you have a different problem. But this is
    > where I would start.
    >
    > -Sean
    > http://OurOdyssey.BlogSpot.com
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