Tie Up and Plug In

Connect your shore-power cord carefully to prevent electrical meltdowns at the dock. From "Hands-On Sailor" in our September 2007 issue

electrical plug 368

To ensure an efficient connection, the shore-power cord¿s locking ring must be fully engaged at the boat¿s receptacle.Steve D'Antonio

Shore power is a truly great convenience, but many sailors don't stop to think about the problems potentially unleashed by bringing it aboard, from the simple nuisance malfunction to the complex and very real risk of fire, shock, or electrocution. While there are a myriad of ways in which shore-power connections, cabling, and appliances can cause trouble aboard a boat, a high percentage of them start at either end of the snaking yellow shore-power cables found at docks everywhere.

Many AC electrical shorts, overheated connections, and, ultimately, fires can be traced to the cable plugs and the receptacle that's installed in the sailboat's cabin side or cockpit. Your boat's electrical system is a mini version of the one used for your home-but with a single important exception: It's temporary, whereas the utility-company wires that enter your home from the street are very permanent indeed. By contrast, the quick-disconnect marine plugs enable you to connect your vessel to shore power when you arrive and disconnect when you're ready to get under way. This convenience, however, is the system's Achilles' heel. If the contacts within the plug and receptacle become corroded-a veritable certainty at some point, given theenvironment-or if they aren't fully engaged-that is, if the plug isn't pushed fully home and twist-locked in place-then the connection may well be compromised.

There's one additional way, perhaps the most common, in which these contacts may become damaged. If the shore-power cable is connected or disconnected from the vessel or the dock pedestal while it's under load, an arc will result. Each time an arc breaches a gap, it creates a micro-pit in the surface of the contact. Eventually, these micro-pits collectively form larger pits. The surface of the pits consists of carbon, which creates resistance within the circuit, which in turn generates heat. This sets into motion a slow but sure cycle. As electrical loads increase-say when the battery charger or refrigerator kicks on-then the heat that's generated also increases, causing the contacts to expand. When the loads decrease, the contacts cool and contract. The cycle makes for a progressively poorer connection that eventually results in visible damage and a possible fire.

Shore-power cables should never be plugged in or unplugged when loads are present. The main shore-power breakers aboard the vessel as well as on the dock should be turned off before the cord is ever touched. Once the connections are completed, then the breakers can be turned on and loads applied.

While we're on the subject, possibly the most frequent misstep involving shore-power cables occurs when the sailor fails to use the cord's locking ring, found on the end of the cord that plugs into the boat's receptacle. This threaded ring must be present, and it must be used every time the cord is connected to the shore power. The locking ring ensures that the cord end remains fully engaged within its receptacle, thereby minimizing the risk of damage.

If your shore-power cable or vessel-side connections show any signs of burning, overheating, or corrosion, repair or replace them. If your locking ring is missing, replace it-they can be obtained from most cord manufacturers-or simply invest in a new cord.

Used properly, your shore-power cord will safely deliver electricity to your boat while it's docked and make your vessel feel just like home.

Steve D'Antonio is a regular Cruising World contributor who offers services for vessel owners, boatbuilders, and others in the marine industry through Steve D'Antonio Marine Consulting (www.steved
marineconsulting.com
).