Vintage American outlet

[wa2ise]

Originally Posted by jeyurkon

Sounds like they're 120 degree apart as in a 3-phase system, instead of 180 degrees in 2-phase. That would explain it adding up to 120. Maybe it was supposed to be 70 volts on each leg and was shifted due to the particular loading of the system.

John

It might be a delta system, 120V on each side of the equilateral triangle. And they probably have a set of three lightbulbs going from each line to the ship's hull. That would yield the 65 to 75V you measured (the mismatch being manufacturing variation of the light bulbs), and all three bulbs would glow dimly. If one line shorts to the hull, the electrical system continues to function, and 2 of the three light bulbs will light up brightly, telling the chief engineer that the short exists, and which phase has the short (the one with the dark light bulb).