Part of understanding your boat's electrical system includes following some basic safety guidelines when working with AC marine electrical equipment and wiring.
1. Be sure that the boat's shore power cord is disconnected and that the auxiliary generator is turned off.
2. Test the wires in the circuit with a voltage tester to make sure the power is turned off. Test from the "hot" (black in 3 wire systems: black & red in 4 wire systems) wire to the ground (green) wire and from the hot wire to the neutral (white) wire. Then test from the neutral wire to the ground wire. The voltage tester should indicate that no voltage is present in the circuit.
3. Be sure the area in which you are working is dry and free of moisture and will remain dry when your work is completed.
4. Keep all electrical wiring as high as practical above bilge water accumulation levels and a safe distance from exhaust systems, fuel systems, and fresh water systems.
5. When completed. check your work with the shore cord connected and The power turned on. Check from the hot wire to both the ground wire and the neutral wire with a voltage tester to insure the proper voltage is present in the circuit. Check from the neutral wire to the ground wire making sure that voltage is not present.
Understanding Your Boat's Electrical System
Through the efforts of the American Boat and Yacht Council (ABYC) industry standards and practices have been established setting forth requirements for the design and installation of alternating current (AC) electrical systems aboard boats. These standards allow the electrical systems to perform their intended functions with minimal fire and shock hazards. The standards also make your boat's AC electrical system easier to understand.
Before we look closely at your boat's AC electrical system, let us review some of the basic principles of electrical theory, For ease of illustration, we will make an analogy comparing your boat's AC electrical system with your body's blood-vascular system, The heart pumps oxygen enriched blood to all parts of your body through a network of arteries, At the heart, the arteries are large, but as they travel through the body, their size is determined by the organ that they supply. Major organs are supplied by larger arteries or several smaller arteries furnishing the necessary blood to satisfy that organ's demand.
Aboard your boat, or from a source shore side, an AC electric generator, raises the voltage, which is the electrical potential, above ground potential (ground potential is rated at zero). The voltage created by the electric generator pushes electric current to your boat's panel board. From the panel board, the heart of your boat's AC electrical system, the electricity is distributed throughout the boat by "hot" wires or ungrounded conductors. The hot wires vary in size depending upon the work they must perform or the demand placed upon them.
When you turn on an AC light or an appliance aboard your boat, a demand or load is placed on the electrical system. Electric current flows through the hot conductor to make the light glow or the appliance operate. Once the electricity has done its work, its potential or pressure drops to zero and it is returned to its source through "neutral" wires or grounded conductors.
Any deviation from the normal flow of electricity is dangerous and could result in fire or shock. Just as your blood vascular system is protected against malfunction, your boat's electrical system has grounding conductors that carry leaking current or abnormal Voltages directly to a safe point of zero voltage, to protect you and your boat from these hazards. The grounding conductor is intended to guarantee that a circuit breaker will open if there is a short circuit or abnormal current flow.
A short circuit occurs when current leaks from a hot wire or connection and reaches a point of zero voltage by some path other than The normal one. The short circuit offers low resistance causing the current to generate enough heat to start a fire. Common causes of short circuits are loose connections, worn insulation, and corrosion.
Since boats equipped with shore power usually remain in the water and mostly saltwater, corrosion becomes the primary cause of failure in electrical equipment. MARINCO provides moisture protection in the form of vinyl covers and a sealing collar system. The covers protect the plug and connector and the sealing collar system provides a mechanical, water tight seal between the cord set and the adapter connection. Failure to use these items can result in much shorter life for your equipment.
In case of saltwater immersion. the device should be rinsed with fresh water, allowed to dry, and then sprayed with a moisture displacement formula product.
If a bare hot wire touches a cover plate or the metallic enclosures of electrical equipment and the cover plate or equipment are not grounded, the voltage of the hot wire would charge the cover plate or the metallic enclosure. If a person touches a charged cover plate or enclosure, the body could provide a path for the current to zero voltage and result in a serious shock. The boat's grounding conductors should connect every outlet and covering plate and the exposed metallic enclosures of electrical equipment to ground, thus minimizing the shock hazard to personnel.
When there is an abnormal current flow or a short circuit, the current bypasses the normal circuit and flows directly to ground without having to perform any work. Because the electricity encounters little resistance, it is high-amperage current. The current is high enough to trip off the circuit breaker and the circuit no longer functions.