AS SEEN IN THE JULY/AUG 2006 ISSUE

Shore-Power for the common boater

If we all lived in a perfect world, our days on the boat would be pleasant, but not too hot. Our nights at dock would be cool and comfortable, with just enough breeze to keep the mosquitoes at bay. All waterfront restaurants would be inexpensive and serve delicious food so we’d never need to cook aboard while visiting distant ports, and our batteries would magically stay charged to full capacity at all times. Somehow, this isn’t the world I live in.

Now, unless you run your generator all the time while at the dock, shore-power is the electrical lifeline for your boat and is what makes boating in Florida and the islands possible for us. It’s so nice to pull into a visiting marina, tie up for the night, plug into the connector, and crank up the air conditioner. We can cook a gourmet meal and even catch our favorite sporting event before turning in for the night. All the while, we know that our batteries will be up to par for tomorrow’s fishing. All of this is possible because of shore-power.

Of course, as with everything else in the real world, it’s not that simple. Shore-power, like land based electrical systems, is so very convenient that we often forget that we must be aware at all times of the dangers involved- dangers that are real.

Shore-power circuitry in simple terms

In many ways, all boat’s AC (alternating current) shore-power electrical systems are extremely similar whether the boat is a large center console, an enclosed bridge sportfisher, or a mega-yacht. The dock, may it be your home port or a visiting port, supplies electric power and an outlet, and the boat supplies the power cord and the connection.

The smallest boats which require minimal shore-power may use nothing more than 15-amp vinyl covered three-conductor electrical cord, something similar to a typical extension cord. Mid-size boats that most of us are accustomed to, use a more robust system to deal with their electrical demands. A 30-amp, 125-volt system is standard, with a connection that is a bit more complex. The 30-amp power inlet on the dock is typically fitted with threaded rings in order to create a safe, watertight connection. From the shore-power inlet, a 30-amp conductor leads to the boat's AC panel, from which power is distributed through the boat by wiring systems called branch circuits.

Larger boats with increased electrical demands use an even stouter system- a 50-amp, 125- volt system. With a 50-amp system, a large boat can provide full sized electric ranges and refrigerators, washer and dryer, complete entertainment systems, and other high-demand appliances. Talk about the comforts of home!

By the way, 15-amp, 30-amp, and 50-amp connectors will not interchange without an adapter. They are designed that way so that they can not be joined together either by mistake or on purpose, because this could lead to serious consequences. Every boat’s onboard electrical panel will provide specific and detailed information about its system requirements.

Things to be aware of…

The AC conductor cable, commonly referred to as the shore-power cord, is the single largest cause of problems with shore-power systems. This umbilical cord is the lifeline which transfers juice from the dock to your boat, and it takes a lot of abuse. Whether the cable is 15-amp, 30-amp, or a big 50-amp one, it is always out in the elements. It flexes, kinks, and is moved thousands of times each day with the motion of the boat at the dock. Shore-power cords get stepped on, run-over by dock equipment, and even pinched between the boat and dock during inclement weather. All of this can damage the cord and put the boat and boater in danger. Don’t hesitate replacing your shore-power cord if you have any doubts.

In both the 30-amp and 50-amp systems, the shore-power cord contains three conductors: the black conductor is "hot" and carries 125-volts of electricity; the white conductor is neutral; and the green conductor is the ground.

Circuit breakers are also of vital importance. Shore-power must have a circuit breaker at the dockside connection and continue unabated into the vessel’s electrical panel. Many boaters believe that just because the dock’s electrical system is equipped with protective breakers, then their boat must already be protected, too. However, if the dockside wiring was done incorrectly, the breaker may be useless. At the ship’s electrical panel there should be a main breaker and individual breakers for each circuit. A typical boat may have a breaker for receptacles, each appliance, air conditioning, etc. All of this equipment must be approved for marine use. If your boat isn’t already equipped with breakers, have the electrical work performed as soon as possible.

At the boat’s electrical panel there should be a polarity indicator. This will indicate that correct polarity is coming in and can save you a serious shock or a short, which in all reality could ignite your boat. This device indicates if wires have been crossed- it happens more often than you think in after-market shore-power and appliance installations. A polarity indicator is also very helpful when visiting a marina other than your home port.

Boaters must keep in mind that the wiring used in marine electrical systems is different from residential wiring. House wiring is in a dry, stable environment. Marine wiring is not so lucky. If a previous owner of your boat used standard Romex house wire in an attempt to upgrade your boat’s electrical system, you need to replace it now. Romex is single-strand copper wire, and it will inevitably crack and break. Boat wiring must be stranded wire, and it should be tinned to help combat corrosion. Wire size varies with the amperage of the boat’s system, but in general, 15 and 20 amp circuits should be wired with 12-gauge wire- nothing lighter. All electrical wiring should be hung as high as possible above bilge water accumulation levels and a safe distance from exhaust, fuel, and freshwater systems.

Grounding the boat’s system is crucial. Grounding of AC circuits protects boaters and equipment by providing a low resistance path for stray electrical volts. Face it, accidents happen. Wires get crossed, wire protective coverings get cut, battery chargers short out, dual-voltage instruments- inverters mostly- can short, and when any of this occurs, AC power can bleed into the DC system. This can be quite harmful to your boat’s electrical system. It can send AC power through the DC wiring, and because the power seeks a ground, it can travel through the engine’s ground connection, through the prop shaft, and into the water. If swimmers happen to be nearby, it can actually cause serious electrocution. At the very least, stray current can cause severe galvanic corrosion to your boat and even nearby boats. Have your boat’s grounding system checked annually. It’s too important to ignore.

Your boat’s power-cord outlet is important. Even if the dock connector is in good shape, the wiring is of the correct nature, and the ground connection is a solid one, if the shore-power connecter on the boat is faulty, a boater can still receive a severe shock. Most outlet problems occur from poor connections. Unlike land-based electrical wiring where the electrician simply tightens screws and secures stripped ends of wire with tape and caps, in boat installations, a crimped terminal or screw-tightened clamp must be used in conjunction with the boat’s stranded wire.

Finally, an often-overlooked part of a boat’s AC shore-power system is a ground-fault circuit interrupter. This inexpensive and easily installed device breaks the circuit if you touch an energized wire. Many older boats are not equipped with GFIs, and they should be. They are the boater’s last defense against an accidental shock.

Get real in your shore-power system

When it comes to boat improvements, we all enjoy claiming “I did it myself!” That’s fine in most cases, but it might not be the best way to go when it comes to your boat’s shore-power system. The best way to make sure that you and your boat- and maybe even your neighbor’s boat- don’t come to harm is to have a qualified marine electrician do any system maintenance and improvements. Unless you are really experienced and trained, marine electrical systems are best left to a professional. However, if you insist on doing improvements yourself, make sure your have the right tools, the correct marine grade wire, and make CERTAIN that the power is disconnected, and the area is clean and dry. Shore-power is serious stuff.

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