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American Boat and Yacht Council, a voluntary standards creating body for the marine industry responsible for Standards and Recommended Practices.


The current carrying capacity of a conductor or device.

Bus Bar

A rectangular conducting bar, usually solid copper or brass, that carries currents to several electric circuits.

CE (Conformité Européenné)

The CE marking is a conformity marking consisting of the letters “CE”. The CE marking is applied to products regulated by certain European health, safety, and environmental protection legislation. The CE marking is obligatory for products it applies to. The manufacturer affixes the marking certifying that the product conforms to applicable regulations, in order to be allowed to sell the product in the European market.

CFR (Code of Federal Regulations)

The written regulations of the United States Federal Government.


A closed path of electrically, or electro-magnetically connected, components or devices that is capable of current flow. Typically consisting of loads, sources, conductors, and circuit protection (circuit breakers and fuses). For example: A battery, fuse, and bilge pump connected together with wire are a circuit. The path must be continuous and closed.

Circuit Breaker

An automatic switch that stops the flow of current in a circuit at a predetermined level without destroying itself.


That part of an electrical circuit whose resistance relative to the balance of the circuit is zero. For example, in a circuit consisting of a light bulb and a battery, connected together with wire, the wire is referred to as the conductor.

Current Rating

The maximum current in amperes that a device will carry continuously under defined conditions without exceeding specified performance limits.

Current Transformer

The “CT”, as current transformers are commonly referred to, is used by AC ammeters to “sense” current flow in a wire in an AC circuit. It is a toroidal coil of wire through which a wire whose current we wish to measure is passed. It is normally encapsulated and looks like a “doughnut”, which is how electricians commonly refer to it. The doughnut has two wires coming out of it, which are connected to the AC ammeter. As current flows in the AC wire we wish to measure, it induces a current flow in the current transformer. The magnitude of the current varies directly with the current flowing in the AC wire. Current transformers are rated by the number of maximum amps that can flow in the measured wire and the current generated, by the CT, at that current flow. For example: A 50:5 CT is rated for 50 amps flowing in the measured wire, and it generates 5 amps of current as a consequence.

DC Grounding Conductor

A normally non-current carrying conductor used to connect metallic non-current carrying parts of direct current devices to the engine negative terminal, or its bus, for the purpose of minimizing stray current corrosion.

Deep - Cycle Batteries

Batteries with thick plates to allow for reserve energy to be stored within the battery plate and released during slow discharge for prolonged periods. The high-density active material remains within the batteries’ plate/grid structure longer, resisting the normal degradation found in cycling conditions. Deep cycle batteries are typically used where the battery is discharged to a great extent and then recharged.

Digital Meter

A digital meter is one that displays values as numerical values rather than as the position of a meter on a relative scale.

Direct Current (DC)

An electric current that always flows in the same direction. The magnitude may vary but the current direction is always the same. Commonly referred to as DC. Examples of direct current sources are batteries, fuel cells, and photovoltaic cells. DC sources such as battery chargers and alternators actually use rectified AC current as the source.

Double Pole

A switch, circuit breaker, or relay that makes or breaks two isolated circuits at the same time.

Engine Negative Terminal

The point at which the engine negative, generally the engine block, is connected to the negative of the battery.

Equipment Leakage Circuit Interrupter (ELCI)

A residual current device which detects equipment ground fault leakage current and disconnects in 120VAC 60Hz systems the hot (ungrounded / black) and the neutral (grounded / white) current carrying conductors at a preset threshold. In a 240VAC 60Hz system, the ELCI disconnects both (ungrounded / black) and the (ungrounded / red) current carrying conductors at a preset trip threshold. The ELCI device meets the requirements of UL 1053 and UL 943 except that the maximum trip level is 30mA and the maximum trip time is 100ms.


A defect in the normal circuit configuration, usually due to unintentional grounding. Commonly referred to as a short circuit.


For an oscillating or varying current, frequency is the number of complete cycles per second in alternating current direction. The standard unit of frequency is the hertz, abbreviated Hz. If a current completes one cycle per second, then the frequency is 1 Hz; 60 cycles per second equals 60 Hz (the standard alternating-current utility frequency).


A conductive device designed to melt when amperage flow through it exceeds a rated amount.

Galvanic Corrosion

Corrosion resulting from dissimilar electrically connected metals being immersed in an electrolyte.

Galvanic Isolator:

A device installed in series with the green grounding conductor of the AC shore power cable designed to block galvanic DC current flow but permit the passage of AC if required.


A rotating machine capable of generating electrical power. In the narrow definition generator refers to a DC machine and alternator refers to an AC machine. However, in common use the term generator is used to refer to AC machines as well.

GFCI (Grounded-Fault Circuit Interrupter)

A safety device that breaks an AC circuit anytime a short to ground occurs; also known as a residual current circuit breaker (RCCB).


Hertz is a unit of frequency of one cycle per second. It replaces the earlier term of “cycle per second (cps).” The abbreviation for Hertz is Hz.


Hot usually refers to the ungrounded current carrying conductors in an AC system. These would typically have a voltage of 120V or 240V in the United States. The term Hot is also used to describe a circuit that is energized, and has a potential greater than ground.

Ignition Protected

A critical designation for any electrical device that is to be used in an area where gasoline, battery, or CNG or LPG vapors may accumulate. The ABYC describes ignition protection as: “the design and construction of a device such that under design operating conditions: it will not ignite a flammable hydrocarbon mixture surrounding the device when an ignition source causes an internal explosion, or it is capable of releasing sufficient electrical or thermal energy to ignite a hydrocarbon mixture, or the source of the ignition is hermetically sealed.” It is important to note that unlike most of the ABYC standards ignition-protection requirements are also mandated by USCG regulations, and compliance is not voluntary, but mandatory.

Interrupt Capacity (AIC)

Maximum short-circuit current at rated voltage which protective device is required to interrupt under operating duty specified and with normal frequency recovery voltage not less than rated voltage.


A device used to change stored DC from a battery source to AC on demand to power appliances.

Isolation Transformer

An AC device consisting of an isolated primary coil, connected to shore power; an isolated copper shield, connected to the shore grounding conductor; and an isolated secondary coil, connected to the onboard bus and magnetically coupled to the primary coil. See ABYC E-11.7.1.

Magnetic Circuit Breaker

Breaker that uses the magnetic field generated by a current-carrying coil to open the circuit.


Refers to the main circuit breaker or bus in a power distribution system. This is the input power source for the system.


National Electrical Manufacturers Association.

Over Current Protection Device

A device, such as a fuse or circuit breaker, designed to interrupt the circuit when the current flow exceeds a predetermined value.


Refers to the electrical charge, which may be positive or negative. It also refers to the positive and negative terminals of a battery or load in a DC system. In AC systems it refers to the connections made to the hot and neutral. There is often a reverse polarity light that indicates if the neutral and hot are reversed.

Polarized System

An electrical system in which the positive and negative or the hot and neutral must be connected in a particular way and cannot be switched. Sometimes there are mechanical preventions to insure the correct polarity.
For example, in an AC plug the physical configuration of the plug and receptacle force a polarized connection.

Reverse Polarity

The unintentional backward connection of the hot (ungrounded / black), the neutral (grounded / white), or grounding (grounded / green) AC shore conductors. This condition can create a shock hazard for personnel in the water near a vessel, boarding a vessel, or onboard a vessel.

Tin Plated

A plating of the element tin, which prevents corrosion. Commonly used to plate copper components such as a power bus.


Underwriters Laboratories Marine Department, POB 13995, 12 Laboratory Drive, Research Triangle Park, NC 27709. Phone: (919) 549-1400. Web site:

UL Listed

Indicates that a device or component has met certain specifications as set forth by Underwriters Laboratory. Further, it means that the device or component has been tested for conformance and ‘listed’ with UL so it can use the UL logo and claim conformance to the specification.

Volt (Voltage)

The unit of electric potential and electromotive force, equal to the difference of electric potential between two points on a conducting wire carrying a constant current of one ampere when the power dissipated between the points is one watt.

Volt - Amps

The product of volts and amps, which is watts in a DC system and the apparent power in an AC system.

Voltage Drop

The loss of voltage as it works its way through a circuit. Excessive voltage drop indicates unwanted resistance in circuit or circuit component.

Wire Amperage Rating

The current a conductor can carry under a set of specified conditions such as open air, in an enclosure, and at a specified temperature.

Wire Sizing

A process to determine the appropriate conductor gauge, stranding, and insulation temperature rating based on length of run (voltage drop), circuit ampacity, ambient temperature, and bundling.