AC Grounding

AC current must alternate between two points making a circuit.

Coming from the power source is the “hot” wire, which normally has black insulation, and returning is the neutral or “grounded” conductor, which is white. “Neutral” carries the same current as the hot wire. As long as the current remains in this closed circuit there is no danger, but if it should escape (a “fault” or “short circuit”), it will attempt to go directly to ground.

Most modern AC circuits have a green third wire, which is a “grounding” wire. It is connected to the third prong of the common three-prong plugs; it parallels the white wire and it connects to neutral at the power source. It’s supposed to ground the circuit when a short occurs.

In a household system the third wire works well as long as three-prong plugs are used and the grounding wire is intact. (Note: it won’t protect you if you touch the hot and neutral wires at the same time.) Household electrical systems are grounded through a metal rod driven into the earth under or next to the building. Between that rod and the people in the house are many layers of wood, concrete and other electrically insulating materials.

In a boatyard, where workers may be standing or crawling on wet ground, there is a potential for electrocution. When a boat is floating, the water is the ground and any metal that has an electrical path to it, including the hull of a metal boat or the engine of a glass or wood boat via the shaft, becomes a path to the ground. Touching any of these items and a hot wire at the same time can send current through the body.

AC Waveforms

When an alternator produces AC voltage, the voltage switches polarity over time, but does so in a very particular manner. When graphed over time, the "wave" traced by this voltage of alternating polarity from an alternator takes on a distinct shape, known as a sine wave: Figure below

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Graph of AC voltage over time (the sine wave).

In the voltage plot from an electromechanical alternator, the change from one polarity to the other is a smooth one, the voltage level changing most rapidly at the zero ("crossover") point and most slowly at its peak. If we were to graph the trigonometric function of "sine" over a horizontal range of 0 to 360 degrees, we would find the exact same pattern as in Table below.

Trigonometric "sine" function.

Angle (o) sin(angle) wave Angle (o) sin(angle) wave
0 0.0000 zero 180 0.0000 zero
15 0.2588 + 195 -0.2588 -
30 0.5000 + 210 -0.5000 -
45 0.7071 + 225 -0.7071 -
60 0.8660 + 240 -0.8660 -
75 0.9659 + 255 -0.9659 -
90 1.0000 +peak 270 -1.0000 -peak
105 0.9659 + 285 -0.9659 -
120 0.8660 + 300 -0.8660 -
135 0.7071 + 315 -0.7071 -
150 0.5000 + 330 -0.5000 -
165 0.2588 + 345 0.2588 -
180 0.0000 zero 360 0.0000 zero

The reason why an electromechanical alternator outputs sine-wave AC is due to the physics of its operation. The voltage produced by the stationary coils by the motion of the rotating magnet is proportional to the rate at which the magnetic flux is changing perpendicular to the coils (Faraday's Law of Electromagnetic Induction). That rate is greatest when the magnet poles are closest to the coils, and least when the magnet poles are furthest away from the coils. Mathematically, the rate of magnetic flux change due to a rotating magnet follows that of a sine function, so the voltage produced by the coils follows that same function.

If we were to follow the changing voltage produced by a coil in an alternator from any point on the sine wave graph to that point when the wave shape begins to repeat itself, we would have marked exactly one cycle of that wave. This is most easily shown by spanning the distance between identical peaks, but may be measured between any corresponding points on the graph. The degree marks on the horizontal axis of the graph represent the domain of the trigonometric sine function, and also the angular position of our simple two-pole alternator shaft as it rotates: Figure below

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Alternator voltage as function of shaft position (time).

Since the horizontal axis of this graph can mark the passage of time as well as shaft position in degrees, the dimension marked for one cycle is often measured in a unit of time, most often seconds or fractions of a second. When expressed as a measurement, this is often called the period of a wave. The period of a wave in degrees is always 360, but the amount of time one period occupies depends on the rate voltage oscillates back and forth.

A more popular measure for describing the alternating rate of an AC voltage or current wave than period is the rate of that back-and-forth oscillation. This is called frequency. The modern unit for frequency is the Hertz (abbreviated Hz), which represents the number of wave cycles completed during one second of time. In the United States of America, the standard power-line frequency is 60 Hz, meaning that the AC voltage oscillates at a rate of 60 complete back-and-forth cycles every second. In Europe, where the power system frequency is 50 Hz, the AC voltage only completes 50 cycles every second. A radio station transmitter broadcasting at a frequency of 100 MHz generates an AC voltage oscillating at a rate of 100 million cycles every second.

Prior to the canonization of the Hertz unit, frequency was simply expressed as "cycles per second." Older meters and electronic equipment often bore frequency units of "CPS" (Cycles Per Second) instead of Hz. Many people believe the change from self-explanatory units like CPS to Hertz constitutes a step backward in clarity. A similar change occurred when the unit of "Celsius" replaced that of "Centigrade" for metric temperature measurement. The name Centigrade was based on a 100-count ("Centi-") scale ("-grade") representing the melting and boiling points of H2O, respectively. The name Celsius, on the other hand, gives no hint as to the unit's origin or meaning.

Period and frequency are mathematical reciprocals of one another. That is to say, if a wave has a period of 10 seconds, its frequency will be 0.1 Hz, or 1/10 of a cycle per second:

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An instrument called an oscilloscope, Figure below, is used to display a changing voltage over time on a graphical screen. You may be familiar with the appearance of an ECG or EKG (electrocardiograph) machine, used by physicians to graph the oscillations of a patient's heart over time. The ECG is a special-purpose oscilloscope expressly designed for medical use. General-purpose oscilloscopes have the ability to display voltage from virtually any voltage source, plotted as a graph with time as the independent variable. The relationship between period and frequency is very useful to know when displaying an AC voltage or current waveform on an oscilloscope screen. By measuring the period of the wave on the horizontal axis of the oscilloscope screen and reciprocating that time value (in seconds), you can determine the frequency in Hertz.

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Time period of sinewave is shown on oscilloscope.

Voltage and current are by no means the only physical variables subject to variation over time. Much more common to our everyday experience is sound, which is nothing more than the alternating compression and decompression (pressure waves) of air molecules, interpreted by our ears as a physical sensation. Because alternating current is a wave phenomenon, it shares many of the properties of other wave phenomena, like sound. For this reason, sound (especially structured music) provides an excellent analogy for relating AC concepts.

In musical terms, frequency is equivalent to pitch. Low-pitch notes such as those produced by a tuba or bassoon consist of air molecule vibrations that are relatively slow (low frequency). High-pitch notes such as those produced by a flute or whistle consist of the same type of vibrations in the air, only vibrating at a much faster rate (higher frequency). Figure below is a table showing the actual frequencies for a range of common musical notes.

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The frequency in Hertz (Hz) is shown for various musical notes.

Astute observers will notice that all notes on the table bearing the same letter designation are related by a frequency ratio of 2:1. For example, the first frequency shown (designated with the letter "A") is 220 Hz. The next highest "A" note has a frequency of 440 Hz -- exactly twice as many sound wave cycles per second. The same 2:1 ratio holds true for the first A sharp (233.08 Hz) and the next A sharp (466.16 Hz), and for all note pairs found in the table.

Audibly, two notes whose frequencies are exactly double each other sound remarkably similar. This similarity in sound is musically recognized, the shortest span on a musical scale separating such note pairs being called an octave. Following this rule, the next highest "A" note (one octave above 440 Hz) will be 880 Hz, the next lowest "A" (one octave below 220 Hz) will be 110 Hz. A view of a piano keyboard helps to put this scale into perspective: Figure below

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An octave is shown on a musical keyboard.

As you can see, one octave is equal to seven white keys' worth of distance on a piano keyboard. The familiar musical mnemonic (doe-ray-mee-fah-so-lah-tee) -- yes, the same pattern immortalized in the whimsical Rodgers and Hammerstein song sung in The Sound of Music -- covers one octave from C to C.

While electromechanical alternators and many other physical phenomena naturally produce sine waves, this is not the only kind of alternating wave in existence. Other "waveforms" of AC are commonly produced within electronic circuitry. Here are but a few sample waveforms and their common designations in figure below

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Some common waveshapes (waveforms).

These waveforms are by no means the only kinds of waveforms in existence. They're simply a few that are common enough to have been given distinct names. Even in circuits that are supposed to manifest "pure" sine, square, triangle, or sawtooth voltage/current waveforms, the real-life result is often a distorted version of the intended waveshape. Some waveforms are so complex that they defy classification as a particular "type" (including waveforms associated with many kinds of musical instruments). Generally speaking, any waveshape bearing close resemblance to a perfect sine wave is termed sinusoidal, anything different being labeled as non-sinusoidal. Being that the waveform of an AC voltage or current is crucial to its impact in a circuit, we need to be aware of the fact that AC waves come in a variety of shapes.

  • AC produced by an electromechanical alternator follows the graphical shape of a sine wave.
  • One cycle of a wave is one complete evolution of its shape until the point that it is ready to repeat itself.
  • The period of a wave is the amount of time it takes to complete one cycle.
  • Frequency is the number of complete cycles that a wave completes in a given amount of time. Usually measured in Hertz (Hz), 1 Hz being equal to one complete wave cycle per second.
  • Frequency = 1/(period in seconds)

Published under the terms and conditions of the Design Science License Disclaimer

Aerator Pump

An aerator pump is a specialized water pump used on fishing boats.

Part of a livewell system, in which a fisherman keeps his catch alive, the aerator (or livewell) pump helps to “aerate” the water and put oxygen into it. This is most often done by re-circulatingAttwood aerator pump - one of the best in boating the water in the livewell through the pump and back to the well via a sprayer that agitates the water and induces oxygen. These are typically known as “recirc” pumps.

Another use for this pump can be as a “pickup”, where it draws in the outside water to fill the livewell or refresh it. The pumps come in a variety of pumping capacities and are powered by 12V DC.

Aerator pumps are manufactured by several well know companies, including Attwood Marine. The Attwood Tsunami Series features innovative engineering and compact design, that delivers high output from a small package.

Attwood aerator pumps are famous for using the most advanced material available, including the best quality bearings and state-of-the-art brushes, alloys and magnets.

They offer three high-efficiency aerator pumps that move water at output capacities of 500 gph, 800 gph and 1200 gph.


An alternator is an electromechanical device that converts mechanical energy to electrical energy in the form of alternating current. Usually the word refers to small rotating machines driven by automotive and other internal combustion engines.

Alternators are used in modern automobiles to charge the battery and to power a car’s electric system when its engine is running. Automotive alternators use a set of rectifiers (diode bridge) to convert the AC output of the alternator to the DC used in vehicle’s electrical system .

Marine alternators used in yachts are similar to automotive alternators, with appropriate adaptations to the salt-water environment. Marine alternators are designed to be explosion proof so that brush sparking will not ignite explosive gas mixtures in an engine room environment. They may be 12 or 24 volt depending on the type of system installed. Larger marine diesels may have two or more alternators to cope with the heavy electrical demand of a modern yacht. On single alternator circuits, the power is split between the engine starting battery and the domestic or house battery (or batteries) by use of a split-charge diode (battery isolator) or a mechanical switch (battery switch)

-adapted from Wikipedia

Anderson Connectors

Anderson connectorsAnderson Connectors or Anderson Plugs as they are more commonly known, are designed for connecting large cables used in high current applications.

Each plug is a mirror of the other and are simple to assemble, There is no Male & Female. One simply connects into another of the same amperage. The plugs push together to form a very solid and reliable connection.

A common application in marine would be in the wiring that distributes AC power.

From the Anderson Power Products website:

Anderson Power Products is an industry leader in the manufacture of high current, quick-disconnect power connectors and provides a variety of interconnect solutions for the material handling, telecommunications, medical, power electronics and other industries. Our connectors are available from 10 to 700 amp maximum ratings for use through 600 Volts continuous, AC or DC operation. We are well known for our ability to develop creative solutions for our customers’ power interconnect requirements. We are flexible and will make modifications to standard products or develop complete custom solutions to satisfy particular customers’ needs. APP provides a complete engineered interconnect solution for all types of power distribution needs.

Basic AC Theory

Most students of electricity begin their study with what is known as direct current (DC), which is electricity flowing in a constant direction, and/or possessing a voltage with constant polarity. DC is the kind of electricity made by a battery (with definite positive and negative terminals), or the kind of charge generated by rubbing certain types of materials against each other.

As useful and as easy to understand as DC is, it is not the only "kind" of electricity in use. Certain sources of electricity (most notably, rotary electro-mechanical generators) naturally produce voltages alternating in polarity, reversing positive and negative over time. Either as a voltage switching polarity or as a current switching direction back and forth, this "kind" of electricity is known as Alternating Current (AC): Figure below

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Direct vs alternating current

Whereas the familiar battery symbol is used as a generic symbol for any DC voltage source, the circle with the wavy line inside is the generic symbol for any AC voltage source.

One might wonder why anyone would bother with such a thing as AC. It is true that in some cases AC holds no practical advantage over DC. In applications where electricity is used to dissipate energy in the form of heat, the polarity or direction of current is irrelevant, so long as there is enough voltage and current to the load to produce the desired heat (power dissipation). However, with AC it is possible to build electric generators, motors and power distribution systems that are far more efficient than DC, and so we find AC used predominately across the world in high power applications. To explain the details of why this is so, a bit of background knowledge about AC is necessary.

If a machine is constructed to rotate a magnetic field around a set of stationary wire coils with the turning of a shaft, AC voltage will be produced across the wire coils as that shaft is rotated, in accordance with Faraday's Law of electromagnetic induction. This is the basic operating principle of an AC generator, also known as an alternator: Figure below

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Alternator operation

Notice how the polarity of the voltage across the wire coils reverses as the opposite poles of the rotating magnet pass by. Connected to a load, this reversing voltage polarity will create a reversing current direction in the circuit. The faster the alternator's shaft is turned, the faster the magnet will spin, resulting in an alternating voltage and current that switches directions more often in a given amount of time.

While DC generators work on the same general principle of electromagnetic induction, their construction is not as simple as their AC counterparts. With a DC generator, the coil of wire is mounted in the shaft where the magnet is on the AC alternator, and electrical connections are made to this spinning coil via stationary carbon "brushes" contacting copper strips on the rotating shaft. All this is necessary to switch the coil's changing output polarity to the external circuit so the external circuit sees a constant polarity: Figure below

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DC generator operation

The generator shown above will produce two pulses of voltage per revolution of the shaft, both pulses in the same direction (polarity). In order for a DC generator to produce constant voltage, rather than brief pulses of voltage once every 1/2 revolution, there are multiple sets of coils making intermittent contact with the brushes. The diagram shown above is a bit more simplified than what you would see in real life.

The problems involved with making and breaking electrical contact with a moving coil should be obvious (sparking and heat), especially if the shaft of the generator is revolving at high speed. If the atmosphere surrounding the machine contains flammable or explosive vapors, the practical problems of spark-producing brush contacts are even greater. An AC generator (alternator) does not require brushes and commutators to work, and so is immune to these problems experienced by DC generators.

The benefits of AC over DC with regard to generator design is also reflected in electric motors. While DC motors require the use of brushes to make electrical contact with moving coils of wire, AC motors do not. In fact, AC and DC motor designs are very similar to their generator counterparts (identical for the sake of this tutorial), the AC motor being dependent upon the reversing magnetic field produced by alternating current through its stationary coils of wire to rotate the rotating magnet around on its shaft, and the DC motor being dependent on the brush contacts making and breaking connections to reverse current through the rotating coil every 1/2 rotation (180 degrees).

So we know that AC generators and AC motors tend to be simpler than DC generators and DC motors. This relative simplicity translates into greater reliability and lower cost of manufacture. But what else is AC good for? Surely there must be more to it than design details of generators and motors! Indeed there is. There is an effect of electromagnetism known as mutual induction, whereby two or more coils of wire placed so that the changing magnetic field created by one induces a voltage in the other. If we have two mutually inductive coils and we energize one coil with AC, we will create an AC voltage in the other coil. When used as such, this device is known as a transformer: Figure below

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Transformer "transforms" AC voltage and current.

The fundamental significance of a transformer is its ability to step voltage up or down from the powered coil to the unpowered coil. The AC voltage induced in the unpowered ("secondary") coil is equal to the AC voltage across the powered ("primary") coil multiplied by the ratio of secondary coil turns to primary coil turns. If the secondary coil is powering a load, the current through the secondary coil is just the opposite: primary coil current multiplied by the ratio of primary to secondary turns. This relationship has a very close mechanical analogy, using torque and speed to represent voltage and current, respectively: Figure below

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Speed multiplication gear train steps torque down and speed up. Step-down transformer steps voltage down and current up.

If the winding ratio is reversed so that the primary coil has less turns than the secondary coil, the transformer "steps up" the voltage from the source level to a higher level at the load: Figure below

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Speed reduction gear train steps torque up and speed down. Step-up transformer steps voltage up and current down.

The transformer's ability to step AC voltage up or down with ease gives AC an advantage unmatched by DC in the realm of power distribution in figure below. When transmitting electrical power over long distances, it is far more efficient to do so with stepped-up voltages and stepped-down currents (smaller-diameter wire with less resistive power losses), then step the voltage back down and the current back up for industry, business, or consumer use use.

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Transformers enable efficient long distance high voltage transmission of electric energy.

Transformer technology has made long-range electric power distribution practical. Without the ability to efficiently step voltage up and down, it would be cost-prohibitive to construct power systems for anything but close-range (within a few miles at most) use.

As useful as transformers are, they only work with AC, not DC. Because the phenomenon of mutual inductance relies on changing magnetic fields, and direct current (DC) can only produce steady magnetic fields, transformers simply will not work with direct current. Of course, direct current may be interrupted (pulsed) through the primary winding of a transformer to create a changing magnetic field (as is done in automotive ignition systems to produce high-voltage spark plug power from a low-voltage DC battery), but pulsed DC is not that different from AC. Perhaps more than any other reason, this is why AC finds such widespread application in power systems.

  • DC stands for "Direct Current," meaning voltage or current that maintains constant polarity or direction, respectively, over time.
  • AC stands for "Alternating Current," meaning voltage or current that changes polarity or direction, respectively, over time.
  • AC electromechanical generators, known as alternators, are of simpler construction than DC electromechanical generators.
  • AC and DC motor design follows respective generator design principles very closely.
  • A transformer is a pair of mutually-inductive coils used to convey AC power from one coil to the other. Often, the number of turns in each coil is set to create a voltage increase or decrease from the powered (primary) coil to the unpowered (secondary) coil.
  • Secondary voltage = Primary voltage (secondary turns / primary turns)
  • Secondary current = Primary current (primary turns / secondary turns)

Published under the terms and conditions of the Design Science License Disclaimer


An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Batteries are a common power source for many household, industrial and transportation applications.Optima deep cycle battery

There are two types of batteries: primary batteries (disposable batteries), which are designed to be used once and discarded, and secondary batteries (rechargeable batteries), which are designed to be recharged and used multiple times.

Rechargeable batteries are what are used in automotive and marine applications. They can be recharged by applying electric current. Devices to supply the appropriate current are engine alternators or chargers.

The most common form of rechargeable battery is the lead-acid battery. This battery is notable in that it contains a liquid in an unsealed container, requiring that the battery be kept upright and the area be well ventilated to ensure safe dispersal of the hydrogen gas produced by these batteries during overcharging.

Battery Boxes

Attwood is the world's most well know manufacturer of battery boxesBattery boxes are used to secure the batteries on a boat against the extreme movement of the craft on water – a marine industry standard and a Coast Guard rule.

While batteries may sometimes be mounted on trays, they are more often stored and held in marine electrical battery boxes, which, besides keeping the battery in place, also protects it from exposure to outside elements like moisture while also containing the corrosive acids of the battery.

Battery boxes also make moving and transporting the battery safe and easy. Battery boxes normally include a box with molded handles, a lid, a strap to hold down the lid and mounting hardware.

Battery boxes are available from several marine manufacturers, although the most well-known are built by Attwood Marine.

Battery Cables

Battery cables are one of the most crucial parts of any boat wiring system.

The foundation of the entire 12 volt marine electrical system is the batteries – both for energy and grounding, which are equally important. For each, the battery cable is a pivotal link.Custom built battery cables give you the correct length, color, gauge and end-fittings for your boat wiring project

Because of the nature of DC power and the easy potential for current loss over distance, battery cables are constructed of thick heavy duty copper and highly insulated. This makes them not only bulky, but expensive.

Good marine electrical design will use the optimal thickness (gauge) of the cables to provide the most current, while attempting to limit the distance they run, as longer runs necessitate increasing the gauge. Typically the cables will be terminated with either battery lugs (for the battery connection) or ring terminals, or most commonly a combination of the two.

Battery cables are available from many sources, although several websites now offer completely custom battery cables. The flexibility of these configurations allows boaters to get precisely the length, color, gauge and end-fittings that their boat wiring project requires.

Battery Management

Battery management is the efficient monitor and control the outflow of power from your boat’s batteries.

The “prime directive” of marine electrical battery management to to avoid the overuse of this finite power supply, which may eventually compromise an important function, like starting your engine. BEP is one of marine electrical's leading suppliers of battery switches for your boat wiring project

Marine electrical battery management can be as simple as monitoring a voltmeter to determine battery voltage; to the use of switches to turn on certain batteries, while isolating others from use ; to having sophisticated voltage sensitive relays that will do the job of monitoring levels and switching batteries on and off automatically – often called a Smart Battery Switch.

Any boater that will be spending time at anchor running electrical accessories, like stereos, will need to maintain some awareness of the condition and level of their battery supply and life. The inability to restart an engine (which is a key source of recharge for the batteries), or to lose the use of a boat’s navigation lighting, boat horns or bilge pumps because of dead batteries is a situation to be avoided. Thus the importance of battery management.