Separate Electrical Systems for DC and AC Power
Most boats have a DC electrical system, so you can start your engine or engines, operate interior lights, pump your bilge and operate marine electronics. Your boat’s DC system most likely operates on either 12V or 24V, from energy stored in the boat’s batteries which are replenished by the boat’s charging system. A second electrical system, your shore power system, allows you to bring AC electricity onboard from a source on the dock. You literally plug your boat into the local utility and enjoy all of the advantages onboard that you’d enjoy in your home or business. Shown above is a typical single phase 120-volt system with shore-grounded (White) neutral conductor and grounding (green) conductor (see ABYC Standards E-11.17.1. Diagram: ABYC®).
While shorepower systems only work when you are plugged in to an external source of AC power at the dock, many boats create their own AC power away from the dock with a generator or an inverter—either of which enables you to enjoy AC power when underway.
Your shore power system allows you to run all sorts of useful appliances and tools on board when you’re in a marina. One of the most common devices is a battery charger to keep your batteries topped off when you’re not onboard. Others include dehumidifiers, heaters, kitchen appliances, power tools, and entertainment products like TVs and stereos.
Shore Power Cords
Your shore power system starts at the dock power pedestal. The conventional system used by mid-sized boats in your local marina combines two circuits with circuit breakers rated at 30A, two female receptacles, and a hinged lid to keep water off the connection. These receptacles have a threaded ring that allows the shore power cord to connect securely and make a waterproof connection. The ideal companion to this outlet is a 30A, 50' cord, by far the most common cord in the U.S. The contacts on the plug will only fit one way into the receptacle, which prevents polarity problems and also provides a secure connection when the plug is twisted slightly clockwise.
Larger boats can satisfy their need for more power using a 50A 125V or a 50A 125/250V cordset, assuming that your marina provides 50A service. While these cordsets can handle lots more amperage than the conventional 30A cords, it’s also common to find some boats using two 30A cordsets. The advantage of using the 50A 125/250V cordset is that you can run 250V products, like stoves other large appliances.
Although most boats use 50' cordsets, Marinco makes shorter models that may be just right for the distance from the pedestal to your inlet. You can reduce expense and clutter by considering one of these 12', 25', or 40' cables, or you can buy shore power cable by the foot, purchase the male plug and female connector separately, and custom-build a cordset to the exact length that fits your slip.
It is vital that you use plugs and receptacles that are intended to be used together, or you could create big problems. Never use a cord that has the bent terminal altered, and never force a plug to fit. The plug should fit easily and stay in place after twisting. For extra security and waterproof protection, always use a weatherproof cover and a threaded ring.
Marinco’s EEL system is more secure than your old cordset.