In North America and some other parts of the world, the most common shore power scenarios are 120 volts AC (alternating current) at 30 amps and 60 Hz (more on that in a moment), often referred to as “single phase” or 120/240 volts AC at 50 amps and 60 Hz, known as “split phase.” In some marinas, especially those in areas with older infrastructure, split phase power might be 120/208 volts AC. You might also encounter 120 volts AC at 50 amps single phase, but that’s not very typical. Outlets aboard vessels, like those in homes, are normally 120 volts, while larger appliances, such as air conditioners and ovens, often operate on 240 volts AC.
The amperage determines how much work can be done by a shore power service. Smaller vessels, up to about 40 feet, with lower power needs, are usually equipped with one or two 120 volt, 30-amp cords. Larger vessels are more power hungry, and thus, they typically utilize one or two 120/240 volt, 50-amp cords.
Shore power frequency, the 60 Hz (which stands for Hertz, sometimes called cycles) part, is the standard in North America. Among other things, frequency determines the speed at which AC-powered motors, fans, and compressors turn.
Shore cord ends are unique to each configuration, making it impossible to plug into the wrong power source.