NUMERIC
240 VAC
The line-to-line voltage in a single-phase three wire (not including green
safety ground) AC system as commonly found in the US.
250 VAC
The line-to-line voltage in a single-phase two wire (not including green safety
ground) AC system as commonly found in the
Europe and many other parts of the world.
3 phase see also single phase
Refers to 3 phase power generation typically 480 VAC and higher. The AC utility
is a 3-phase system. In its simplest form there are three conductors connected
to three conductive coils, which pass through a magnetic field, thus, inducing
the electrons in the wires to flow. As the polarity of the magnetic field
changes from North to South, electrons are induced to flow first one way then
the other. This produces AC current flow. The current that is induced in the
three wires is 120° out of phase. The current flow in the first conductor
starts 120° before the second and it starts 120° before the third.
Three phase generators are only found on the largest boats.
120 VAC
The line to neutral voltage in a single phase three wire AC system
as commonly found in the US.
3 stage charging
A technique of
battery charging that uses three distinct phases to ensure a fast and complete
charge and a safe maintenance
voltage. As there are several manufactures of multiple stage charging systems,
there is a slight difference in terminology in the field. See each key word
for a more complete definition.
Stage 1: Charge or Bulk Mode
Stage 2: Acceptance or Absorption
Stage 3: Float
A back
to the top
AC see Alternating Current
ABYC
American Boat and Yacht Council, a voluntary standards creating body for the
marine industry responsible for Standards and Recommended Practices.
AIC Amperes Interrupt Current see Interrupt
Rating
AGC Fuse
A 1-1/4 inch long x 1/4 inch diameter glass fuse with fast blow characteristics.
ATO/ATC Fuse
The
blade type fuse now commonly used in the automobile industry. It has fast
blow characteristics like the AGC fuse.
absorption see 3 stage charging, see also
float, bulk, equalize
Absorption refers to the second phase of a multistage charging system, also
called acceptance by some manufacturers. During the absorption cycle the battery
is maintained at the maximum charging voltage. Typically about 2.4V per cell
or 14.4V for a typical 12V system. (28.8V for a 24V system). This is the gassing
voltage for a liquid battery. Gelled batteries are typically charged at slightly
lower voltages. The gassing voltage is also temperature dependent. The battery
cannot be maintained for long periods of time in the absorption phase.
acceptance see absorption
alternating
current
A periodic current (sine wave) whose average value over a cycle is zero. The
current reverses at regular intervals of time and has alternately positive
and negative values.
alternator
Commonly refers to the DC charging source on an engine. The alternator is
a three-phase AC device that produces alternating current which is then rectified
by a diode bridge to create direct current. Three phase AC devices are reliable
and inexpensive to make compared to a DC generator of the same capacity.
alternator
field disconnect
The alternator field is created by a coil of wire surrounded by ferrous metals.
When the coil is energized with electric current it becomes an electromagnet.
This electromagnet is rotated, inducing a current flow in the three phase
coils that surround it. By controlling the strength of the magnetic field,
the output of the alternator may be controlled. If the output of the alternator
is open circuited there is no place for the energy to go. The voltage rises
to a dangerous level. By disconnecting the alternator field, the magnetic
field is turned off, thus the voltage cannot soar. This is a safety feature
on some battery switches.
ambient
temperature
The temperature of the medium in which the heat of a device is dissipated.
The ambient temperature is often specified in standards for device performance
(such as the UL Standards) as the basis for determining the heat rise of the
component.
ammeter
Measures current flow in a circuit. An ammeter is inserted in series in the
circuit. We consider four types:
Analog
The classic analog ammeter uses the magnetic field associated with current
flow through a moving coil of wire, to in turn move a needle over a meter
face which displays amps. This type of meter can only measure very small current,
micro-amps, before the moving coil become too large to be practical. To measure
higher currents a shunt resistor is inserted into the circuit. (see Shunt).
Most of the current flows through the shunt resistor but some passes through
a meter movement as described to read amps when the movement is scaled appropriately.
Digital DC
The digital DC ammeter uses a shunt resistor to measure current flow. (see
Shunt) . The shunt is connected in series in the wiring of the circuit whose
current is to me measured. The shunt sense leads are connected to the DC ammeter,
which is really a millivolt meter. The millivolt input from the shunt is scaled
to read amps per the resistance of the shunt. For example, a current flow
of 10 amps through a 100A-100mV shunt would result in a voltage of 10mV across
the sense leads. A millivolt meter would display 10, which we would interpret
as 10 Amps.
Digital AC
The digital AC ammeter also uses a shunt resistor to measure a voltage drop,
which is then scaled to read amps. The difference, however, is that the resistor
is not normally connected directly in the AC wire of the circuit to be measured.
A device called a current transformer (CT, see Current Transformer) is placed
around the AC wire. A current is induced in the CT, which is then passed through
a load resistor. The digital meter actually measures the voltage across this
load resistor and internally
scales it to read the appropriate number of amps.
Portable
Most portable meters today are digital and use the same techniques of measurement
as described above. The main differences are they commonly are limited to
a few amps when connected in series to measure current. If high currents are
to be measured the portable meter must use some external sensing means. Commonly
these consist of shunt resistors and clamp on ammeter sensors that use Hall
Effect sensors. (Operation of which are beyond the scope of this appendix.
Suffice it to say they generate a voltage, which can be scaled to read amps
just as the shunt resistor.)
ampacity
The current carrying capacity of a conductor or device.
ampere
see coulomb
1) The classic definition of an ampere is a unit of electric current flow
equivalent to the motion of 1 coulomb of charge, or 6.25 X
10 18 electrons, past any cross section in 1 second. This is an intuitive
way to think about an ampere, it is the flow of a huge number of electrons
through a conductor. 2) In 1948 this alternative definition was adopted: A
unit of electric current in the meter-kilogram-second system. It is the steady
current that when flowing in straight parallel wires of infinite length and
negligible cross section, separated by a distance of one meter in free space,
produces a force between the wires of 2 x 10 -7 newtons per meter of length.
ampere-hour
The electric charge transferred past a specified circuit point by a current
of one ampere in one hour.
Amp-Hour Rating (AH)
This is a common rating for batteries. This is the total number of ampere-hours
that a battery can deliver over 20 hours at a constant rate of discharge before
the battery voltage falls below 10.5 volts.
analog
Refers to a signal or input that varies continuously over time. Voltages and
currents are analog signals, as is temperature, pressure, and levels.
anode
The electrode of an electrochemical cell with the more negative potential.
The less noble metal of an electrolytic cell that tends to corrode
AWG
(American Wire Gauge)
see also SAE wire gauge
AWG (American Wire Gauge) is a US standard set of nonferrous (copper or aluminum)
wire conductor sizes. The "gauge" means the diameter. Typical household
wiring is AWG number 12 or 14. Telephone wire is usually 22, 24, or 26. The
higher the gauge number, the smaller the diameter and the thinner the wire.
Thicker wire can carry more current because it has less electrical resistance
over a given length. Thus larger wire is used when the voltage drop along
its length must be minimized. For example: High output alternator wiring might
be a 2 AWG and the starter cable for a modest engine a 1 or 0 AWG.
battery
see also cell
Two or more cells connected together. Thus a group of batteries connected
together can also be referred to as a battery
battery
bank
When groups of 6V or 12V batteries are wired in series or parallel or a combination
to increase voltage or capacity the entire group is referred to as a battery
bank. When batteries are connected in series the amp-hour rating is the same
and the voltage is additive. When batteries are connected in parallel the
voltage is the same and the amp-hour rating is additive.
battery
state-of-charge
The term is used to describe and estimate of how much energy the battery is
able to deliver. There have been many attempts to develop improved state-of-charge
estimates. The most common methods include: specific gravity, at-rest open-circuit
voltage, and amp-hour measurement.
battery
switch rating see Continuous switch rating and
Intermittent switch rating
battery types
AGM (Absorbed Glass Mat)
A technique for sealed lead-acid batteries. The electrolyte is absorbed in
a matrix of glass fibers, which holds the electrolyte next to the plate, and
immobilizes it, preventing spills. AGM batteries tend to have good power characteristics,
low internal resistance, and good behavior during charging.
Flooded
A design for lead-acid batteries. The electrolyte is an ordinary liquid solution
of sulfuric acid. Flooded cells are prone to making gas while being charged.
Flooded cells must be periodically checked for fluid level and water added
as necessary. Flooded cells are also typically less expensive than AGM or
gel type lead-acid batteries.
Gel cell
Gel or sealed lead acid batteries are basically the same chemistry as a wet
(flooded cell) battery. The batteries' electrolyte is in a gelatin form and
is absorbed into the plates and the battery is sealed with epoxies. The batteries
are exceptionally leak resistant and may be used in any position. Battery
uses are UPS, emergency lights, and camcorders. These batteries are 2 volts
per cell, so the common batteries are 4, 6, and 12 volt.
blade
That portion of a fuse to which the fuse block connects.
bonding,
cathodic
The electrical interconnection of metal objects in common contact with water,
to the engine negative terminal, or its bus, and to the source of cathodic
protection.
branch
circuit see also main
The portion of the wiring system after the main circuit protection device.
break
(rating)
The amount of current that can be passing through a set of contacts, such
as those in a solenoid, when they open, without damaging the contacts. This
can be a rating for a single event or over some number of cycles, generally
1000, 10,000 or 1000,000.
bulk
That part of a multistage charge regime in which the maximum amount of current
is flowing. This is normally limited by the size of the charging source. Lead
acid batteries have the ability to accept, or absorb, large charging currents
as long
as they do not overheat or begin gassing. The bulk cycle allows the fastest
possible charge.
bus,
busbar
A bus is a group of common connections, often consisting of a strip of copper
or brass with a number of screws or bolt studs for the connection of wires.
It may be a negative or a positive bus.
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 his product in the European market.
cathode
The electrode of an electrochemical cell with the more positive potential.
The more noble metal of an electrolytic cell that tends not to corrode
cell
An electrochemical system that converts chemical energy into electrical energy.
Typically consisting of two conductive plates with different galvanic potential
immersed in an electrolyte.
cell, primary
An electrochemical device, which is discharged only once and then, discarded
cell, secondary see also battery
An electrochemical device, which may be discharged and recharged a number
of times
CFR
(Code of Federal Regulations)
The written regulations of the United States Federal Government.
charge
Classically refers to an accumulation of electrons producing an electrostatic
charge. In common use it often refers to restoring energy to a battery. Specifically,
it would refer to the part of a multistage battery charging cycle when the
voltage was held constant at or about the gassing voltage.
charge
cycle
The stages through which a multistage charging source restores energy to a
battery. A four-stage charge cycle includes:
bulk or charge cycle: Constant current for fast charging
acceptance or absorption cycle: Constant voltage for thorough charging
float cycle: For maintenance and long life
equalization cycle: Controlled overcharge for maximum capacity.
see key words above
circuit
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
A device that, like a fuse, interrupts a current in an electric circuit when
the current becomes too high. Unlike a fuse, a circuit breaker can be reset
after it has been tripped. When a high current passes through the circuit
breaker, the heat it generates or the magnetic field it creates causes a trigger
to rapidly separate the pair of contacts that normally conduct the current.
Circular
mils
A method of specifying wire size mathematically. One Circular Mil is a unit
of area equal to that of a circle .001" in diameter. The actual area
of a Circular Mil is:
A = ð r 2
A = 3.1428 x (.0005)2 inches
A = .0000007857 square inches
Class-T
fuse
A very robust fuse carrying a 20,000 AIC. It also has very fast response to
short circuit currents.
Cold Cranking Amperes (CCA) see also Marine Cranking
Amperes
CCA is the discharge load in amps which a battery can sustain for 30 seconds
at 0° F. and not fall below 1.2 volts per cell (7.2V on 12V battery).
This battery rating measures a burst of energy that an engine needs to start
in a cold environment. This rating is used mainly for rating batteries for
engine starting capacity and does not apply to NiCad batteries, NiMH batteries
or Alkaline batteries.
coil
see inductor
Conformité
Européenné see CE
continuous
current
The current flow which a device or a conductor can carry, consume, or supply
with no time limit. The continuous current rating is normally dependent on
the temperature, since resistance increases with temperature. For battery
switches the continuous current rating is established by testing for one hour
at the rating. This is reasonable since thermal equilibrium would be reached
within one hour.
continuous
switch rating (UL)
There are two ratings in the UL marine battery switch standard, Intermittent
and Continuous. Intermittent is a 5 minute rating and is based on temperature
rise of various sections of the switch as the rated current is applied over
a 5 minute period. The Continuous rating is the same, but the time period
is 1 hour.
conductivity
Conductance is the reciprocal of resistance, which depends on the receptivity
constant of the material. Receptivity is the resistance of a conductor having
unit cross section and unit length. Conductivity is the reciprocal of the
receptivity. Its units are 1/ohm-cm or moh/cm, or 1/ohm-circular mils/ft.
conductor
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.
converter
An electrical device that converts one type of electrical energy into another.
Battery chargers convert AC power to DC to charge the battery, inverters convert
DC power into AC, both are converters. Often used in RV industry to mean a
power supply that runs the domestic DC loads when shore power is available.
common
May have more than one meaning. Typically denotes a bus that is at ground
potential most often. The negative bus is called "the common", sometimes
the neutral bus is also called "the common". May also mean a group
of connections that are connected together "in common" even they
are a different potential than ground.
coulomb
see also amperage
The measurement unit of electric charge, which is determined by the number
of electrons in excess (or less than) the number of protons. Classically a
charge of 1 coulomb = 6.25 X 10 18 electrons. The meter-kilogram-second unit
of electrical charge equal to the quantity of charge transferred in one second
by a steady current of one ampere.
counterpoise
That portion of an antenna system composed of wires or other types of conductor
arranged in a circular pattern at the base of the antenna at a certain distance
above ground. Insulated from the ground, it forms the lower system of antenna
conductors.
cranking
(starting)
Normally associated with "cranking current" which is the current
required by the starter circuit prior to engine starting. The cranking current
varies significantly during the starting cycle. Initially, there is a large
surge of current required to overcome the inertia and compression of the engine.
This surge can be two to four times the average cranking current. Once the
engine is turning there are peaks and valleys as the pistons go through the
compression and exhaust cycles. The cranking current rating is used for sizing
batteries, cables, and battery switches.
current
see also amperage
Current is a flow of electrical charge carriers, usually electrons or electron-deficient
atoms. The common symbol for current is the uppercase letter I. The standard
unit is the ampere, symbolized by A. Physicists consider current to flow from
relatively positive points to relatively negative points; this is called conventional
current or Franklin current. Electrons, the most common chargecarriers, are
negatively charged. They flow from relatively negative points to relatively
positive points. Electric current can be either direct or alternating. Direct
current (DC) flows in the same direction at all points in time, although the
instantaneous magnitude of the current might vary. In an alternating current
(AC), the flow of charge carriers reverses direction periodically. The number
of complete AC cycles per
second is the frequency, which is measured in hertz. An example of pure DC
is the current produced by an electrochemical cell. The output of a power-supply
rectifier, prior to filtering, is an example of pulsating DC. The output of
common utility outlets is AC.
current
rating
The maximum current in amperes that a device will carry continuously under
defined conditions without exceeding specified performance limits.
current transformer see also ammeter
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.
cycle
A cycle of a battery is a discharge plus a charge. For example, if a fully
charged battery has a load applied, is then discharged and recharged, that
is one cycle. Cycle life is the total number of cycles a battery yields.
DC
see direct current
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.
derating
A decrease in a device's rating, usually amperage, due to its application
in ambient conditions different from those in which it was tested or for which
it was designed originally.
delay
A difference in time between the initiation of an event and its occurrence,
or between an event's observation and enunciation
of it. This is usually used to refer to the time between the application of
rated amperage to a fuse or circuit breaker and the time when the device opens.
dielectric
strength
The maximum voltage stress that a material can withstand without rupture.
digital
A digital signal is one which has only two valid values denoted as 1 or 0.
Commonly these are equated to distinctly different
voltage. For example: A voltage of +5V would equal a 1 and a voltage of 0V
would equal a 0. 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.
discharge
Refers to the consumption of energy from a battery, or to the electrostatic
discharge associated with a lightning bolt, capacitor, etc.
double
insulation system
An insulation system comprised of basic insulation and supplementary insulation,
with the two installations physically separated and arranged so they are not
simultaneously subjected to the same deteriorating influences to the same
degree.
double
pole
Indicates a switch, relay, or circuit breaker with two separate conductive
paths, which are opened or closed when the device is operated.
Earth
The third planet from the sun in Astronomy, but in electrical terms it refers
to a connection, which is made to a conductor that is connected to the planet
Earth. In grounded electrical systems there is a connection, which is a copper
rod or some other highly electrically conductive connection, to the actual
Earth. This is to ensure a safe conductive path for a short circuit, which
in turn helps prevent electrocution.
electrode
A conductive material, in an electrolyte, through which electrical current
enters or leaves
electrolysis
Chemical changes in a solution, or electrolyte, due to the passage of electric
current.
electrolyte
A liquid in which ions are capable of migrating and, therefore
capable of conducting current. Solutions of acids, bases, and
salts in water are electrolytes.
electron
see also coulomb
An electron is a negatively charged subatomic particle. It can be either free
(not attached to any atom), or bound to the nucleus of an atom. In electrical
conductors, current flow results from the movement of free electrons from
atom to atom individually, and from negative to positive electric poles in
general. The charge on a single electron is considered as the unit electrical
charge. It is assigned negative polarity. Electrical charge quantity is not
usually measured in terms of the charge on a single electron, because this
is an extremely small charge. Instead, the standard unit of electrical charge
quantity is the coulomb, symbolized by C, representing about 6.25 x 10 18
electrons.
electromotive
force (EMF)
Commonly referred to as voltage, electromotive force is the energy per unit
of charge that is supplied by a source of electrical energy such as a battery,
charger or alternator.
Electromagnetic
Interference (EMI)
Noise generated by a load (typically by electrical switching action). Usually
specified as meeting agency limits for conducted EMI (noise reflected back
onto the power bus) or radiated EMI (noise emitted into the area surrounding
a device).
energy
see also Power
The classically simple definition is, the capacity to do work. Energy may
be manifested as, mechanical motion, thermal heat, or electrical power, which
is consumed, radiated, dissipated, or stored over a period of time. The energy
in a direct-current circuit is equal to the product of the voltage in volts,
the current in amperes, and the time in seconds. The units for energy are
Watt-hours. In alternating current (AC) circuits, the expression for energy
is more complex.
engine
negative terminal
The point at which the engine negative, generally the engine block, is connected
to the negative of the battery.
equalization
see charge cycle
Equalization is a controlled overcharge, which removes lead-sulfate that is
not converted during normal charging. Equalization is best accomplished by
using a constant current of 2-7% of battery capacity while allowing the battery
voltage to rise to its highest "natural voltage". For a 12V battery
this can be as high as 16.2V. The equalization cycle is continued until the
specific gravity of all cells cease to continue to rise and are approximately
equal. The equalization cycle should only be used on liquid electrolyte batteries
and only while the operator is on the premises.
fast
(fast acting) see also delay
Refers to the amount of time that a fuse can endure an over-current before
blowing. Fast fuses are used to protect sensitive equipment.
fault
A defect in the normal circuit configuration, usually due to unintentional
grounding. Commonly referred to as a short circuit.
float
charge (see also bulk, acceptance, equalization) A constant voltage,
well below the gassing point, that is applied to a battery to maintain its
capacity. The voltage is such that neither charging nor discharging is occurring.
field
Typically refers to a magnetic field. Specifically used when discussing the
rotating electo-magnetic field associated with an alternator. By varying the
field current, thus its strength, the output of the alternator may be controlled.
fuse
Safety
device, consisting of a strip of low-melting-point alloy, which is inserted
in an electric circuit to prevent excess currentfrom flowing. If the current
becomes too high the alloy strip melts, opening the circuit.
fusible
link
A type of fuse with a replaceable conductive alloy link that may be replaced
if it "blows" due to over-current.
frequency
see also Hertz
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).
galvanic
corrosion
The corrosion that occurs at the anode(s) of a galvanic cell.
galvanic
isolator
A device installed in series with the (AC) grounding (green) conductor of
the shore-power cable to effectively block low
voltage DC galvanic current flow, but permit the passage of alternating current
(AC) normally associated with the (AC) grounding (green) conductor. This is
typically two diodes wired in parallel facing opposite directions, sized to
meet full fault current.
galvanic
series
A list of metals and alloys arranged in order of their potentials as measured
in relation to a reference electrode when immersed in seawater. The table
of potentials is arranged with the anodic or least noble metals at one end,
and the cathodic or most noble metals at the other
generator
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.
green
wire
The green wire is the non-current carrying safety grounding wire in an AC
system in the United States. It is connected to an exposed metal part in the
electrical system to provide a path for fault current in the case of a short
circuit.
ground
fault
GFI (Ground Fault Interruptor)
GFI is generic term referring to both GFCI and GFP
GFCI (Ground Fault Circuit Interruptor) see GFI
A device intended for the protection of personnel that functions
to de-energize a circuit, or portion thereof, within an established
period of time when a current to ground exceeds some
predetermined value that is less than that required to operate the
overcurrent protective device of the supply circuit.
GFP (Ground Fault Protector) see GFI
A device intended to protect equipment by interrupting the electric current
to the load when a fault current to ground exceeds some predetermined value
that is less than that required to operate the overcurrent protection device
of that supply circuit.
ground,
ground conductor
A point in a circuit which is at zero potential with respect to the Earth,
or which is at the lowest potential in the system, (as with a floating ground).
grounding,
grounding conductor
The AC conductor, not normally carrying current, used to connect
the metallic non-current carrying parts of electrical equipment to
the AC system and engine negative terminal, or its bus, and to
the shore AC grounding conductor through the shore power cable.
This term can also refer to the 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, to minimize stray current corrosion.
ground
plate
A conductive plate, commonly sintered copper, that is placed in contact with
seawater to provide a connection to earth for a boat's ground systems.
grounded
The AC current carrying conductor that is intentionally maintained at ground
potential, also called neutral.
Hertz
see frequency
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
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.
Impressed
current
Direct current supplied by a device employing a power source external to the
electrode system of a cathodic protection installation. The impressed current
is used to counteract the undesired galvanic current.
inductance
An effect in electrical systems in which electrical currents store energy
temporarily in magnetic fields before that energy is returned to the circuit.
inductor
see coil
A length of wire that is wound around a core that is used as a storage element
for a magnetic field in an electric circuit.
inrush
The momentary steep wave front of of very high current exhibited by a load
on initial application of power.
interrupt
rating (AIC)
The fault current that a device, normally a fuse or circuit breaker is capable
of breaking without damage.
inverter
An inverter converts DC power stored in a battery to AC power which is used
by most household appliances.
IP
ignition protection
Devices, which operate in a potentially explosive environment, must be ignition
protected. This would include engine rooms with gasoline engines. There is
a very specific set of tests which a device must pass to claim ignition protection.
They include operating safely in an explosive mixture of propane and air.
isolation
transformer
A transformer that is inserted in series with the incoming AC power to provide
a magnetic coupling for power between the ship's systems and the AC grid.
By magnetically coupling the power there is no direct connection by wires,
which isolates the ships AC system from the AC grid.
isolator
Refers to two or more diodes wired in parallel and then inserted in series
with the output of an alternator. This allows for the alternator to charge
multiple batteries. The voltage drop across the diodes can cause incomplete
charging. Isolators should not be used with alternators that use internal
voltage sensing for regulation. To be properly installed the voltage sense
lead must come from the house battery.
kilo
A prefix in the metric system equal to 1000 times, as inkilohertz, 1000 cycles
per second.
line
see also load
The conductors that are at the supply of energy to a circuit. Line normally
refers to the current carrying non-grounded
line
loss see voltage drop
The power loss that occurs due to amperage flowing through the resistance
of conductors over their length.
listed
(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.
load
see also line
A device that consumes power and does work.
load
group
A collection of loads, which normally have similar characteristics. For example
the lighting circuits might be considered a load group. Also implies that
the loads are supplied by a common
bus.
lockouts
(AC)
Mechanical or electrical devices or protection systems, that prevent the application
of more than one source of power to a bus at the same time.
magnetic
Displaying the characteristics of a magnet, including being able to induce
current flow in a conductor when relative motion exists between them and being
able to attract ferrous materials.
main see also branch
Refers to the main circuit breaker or bus in a power distribution system.
This is the input power source for the system.
make
(rating)
The current that a breaker, switch, or relay can connect without damaging
the device.
make
before break
Describes a switch action that connects the new circuit before disconnecting
the old. This type of switch action is required for battery switches in order
to avoid an open circuit for the engine alternator, which can cause extreme
voltages that can damage the alternator and accessory electronics.
Marine
Cranking Amperes (MCA)
MCA is the discharge load in amps, which a battery can sustain for 30 seconds
at 32°F. and not fall below 1.2 volts per cell (7.2V on 12V battery).
This battery rating measures a burst of energy that an engine needs to start
in a cold environment.
modified
sine wave
A marketing term to describe an AC waveform, created by an inverter that is
a pulse width controlled square wave. While an improvement on the classic
square wave inverter, it is not actually a sine wave or a close approximation.
momentary
switch rating (UL)
There are two ratings in the UL marine battery switch standard, intermittent
and Continuous. Intermittent is a 5 minute rating and
NEC
see National Electrical Code
NEMA
National Electrical Manufacturers Association
N-type
(alternator)
An N-type alternator has a set of diodes, called the diode trio, which supply
the positive DC potential required for the rotating field current. The actual
regulator switches the negative to achieve the proper field strength to create
the desired correct alternator output.
National
Electrical Code NEC
The NEC is developed and maintained by the National Fire Protection Association
which describes how residential, commercial, and RV electrical systems must
be installed. The NEC is adopted, sometimes with revision, by states that
also adopt the Uniform Building Code. Electrical inspections required by most
building permits follow the NEC. While not required aboard boats, the NEC
is a valuable guide to safe electrical systems. The goal of the NEC is personnel
safety and fire prevention
neutral-to-ground
bonding
Connecting the ground and the neutral together via an electrical conductor.
neutral-to-ground
switching
In the US, inverter/charger installations that are used in marine applications
must have ground-to-neutral switching. This guarantees that the neutral and
the green wire are common after the green wire connection to neutral that
is achieved through the shore power cord no onger exists after the cord is
disconnected and shore AC is no longer serving as the boat's AC source. There
must also be only a single ground point in the AC system. This prevents a
voltage differential from developing between the boat's AC neutral and the
shore or genset AC neutral, which may cause an electric shock or nuisance
tripping of GFI's.
neutral
(ground) see also single phase
The neutral is the grounded current carrying conductor in a single phase,
four wire, 120/240V AC system.
non-inverter
loads
Non-inverter loads are heavy loads that are not appropriate to run from an
inverter because the load on the batteries would be excessive or illogical.
They include hot water heater, electric space heat, air conditioning, heavy
pumping loads, etc. A battery charger that supplies
the same battery as is being used by the inverter would also be a non-inverter
load.
nuisance
trip
A circuit breaker or fuse, which trips or blows without the circuit actually
being overloaded. This may be due to weak breaker or a surge current which
requires a slow tripping breaker or a slow blow fuse.
O
back to the top
Ohm's
law
States that the ratio of the EMF (Electromotive Force) applied to a closed
circuit to the current in the circuit is a constant. That constant is the
resistance of the circuit. It may be stated as V= IR (or E=IR, using E as
the abbreviation of EMF whose units are volts). The unit of resistance is
the ohm.
ohm
The unit for resistance equals V/I = volt/amp. The unit of resist-ance is
the ohm, symbol ?, the Greek letter Omega.
overcurrent
When the current in a circuit exceeds the rating of the devices or conductors
in it. Fuses and circuit breakers protect from overcurrent buy opening the
circuit if such a condition exists and persists.
open
Indicates a condition in an electric circuit in which there is a break in
the conductive path. The break may be intentional such as a open switch or
relay or it may be unintentional such as a broken wire or a blown fuse. In
any case, the continuous conductive path required for an electric circuit
is not available.
open
circuit voltage
Generally, the voltage of a source when it is not connected to a load through
an electrical circuit. Specifically, the voltage of a battery when it is not
delivering or receiving power. A typical value for a liquid lead acid battery
is 12.8V for a fully charged battery
which has not been charged or used for 24 hours. Open circuit voltage is sometimes
used as an indicator of the state-of-charge of a battery.
The table below gives typical open circuit voltages for both liquid and gelled
electrolyte lead-acid batteries at various states-of-charge. These voltages
should be considered approximations and
may vary according to manufacturer and the specific gravity of the electrolyte
the battery is initially filled with.
P back
to the top
P-type
(alternator)
A P-type alternator is one which one end of the coil which supplies the rotating
magnetic field is connected to the negative and the regulator controls the
positive side of the coil to regulate the alternator output.
panelboard
A collection of circuit breakers, switches, and instrumentation installed
into a panel which provides the central point for power distribution and monitoring
for the electrical system. May also refer to a smaller panel which is located
remotely from the main panel which is used to supply loads in the adjacent
area. "Panelboard" is a term generally used only by ABYC. In the
marine industry they are usually called "panels", or "circuit
breaker panels", or "distribution panels".
parallel
circuit
An electrical circuit in which the positive connections are all in common
and the negative connections are all in common. The voltage of the system
appears across each branch of the circuit. The current varies as required
by each load or source.
paralleling
switch
Typically refers to a battery switch that allows multiple batteries to be
connected together for engine starting. Often used to connect the battery
serving the domestic system to the engine starting circuit for emergencies.
parallel device
A switch, solenoid, relay, or solid state device which is used to connect
multiple batteries or busses together.
Peukert's
equation
A formula that shows how the available capacity of a lead-acid battery changes
according to the rate of discharge. The capacity of a battery is expressed
in Amp-Hours, but the simple formula of current times hours does not accurately
represent the situation. Peukert found that the equation: C = I n T fits the
observed behavior of batteries. "C" is the theoretical capacity
of the battery, "I" is the current, "T" is time, and "n"
is the Peukert number, a constant for the given battery. The equation captures
the fact that at higher discharge currents, there is less available energy
in the battery.
pigtail
Wires which protrude from a device to connect it to the circuit. Often used
in encapsulated products. Sometimes refers to a method of hooking up circuits
in which a group of conductors are connected together and then one wire is
connected to the circuit, this is done in order to simplify wiring.
percent
of charge
An estimate of the remaining charge in a battery. Percent of charge is very
difficult to determine accurately without sophisticated microprocessor based
calculations.
plate
(battery)
Flat, typically rectangular components that contain the active material, lead
or lead compound, and a mechanical support structure called a grid, which
also has an electrical function, carrying electrons to and from the active
material. Plates are either positive or negative, depending on the active
material they hold.
polarity
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.
pole
see also toggle
Indicates a conductive path in a switch or relay. Switches that are single
pole have one conductive path, switches that are two pole have two conductive
paths. Also refers to the magnetic poles on an electromagnet or a permanent
magnet
potential
The voltage across a circuit element. Implies the potential to do work.
power
Electrical power is the rate at which electrical energy is converted to another
form, such as motion, heat, or an electromagnetic field. The common symbol
for power is the uppercase letter P. The standard unit is the watt, symbolized
by W. In utility circuits, the kilowatt (kW) is often specified instead; 1
kW = 1000 W. Power in a direct current (DC) circuit is equal to the product
of the voltage in volts and the current in amperes. This rule also holds for
low-frequency alternating current (AC) circuits in which energy is neither
stored nor released. At high AC frequencies, in which energy is stored and
released (as well as dissipated or converted), the expression for power is
more complex. In a DC circuit, a source of V volts, delivering I amperes,
produces P watts according to the formula: P = VI When a current of I amperes
passes through a resistance of R ohms, then the power in watts dissipated
or converted by that component is given by: P = I 2 R When a potential difference
of V volts appears across a component having a resistance of R ohms, then
the power in watts dissipated or converted by that component is given by:
P =V 2 /R
power
factor
In an AC circuit loads other than resistance shift the phase angle between
the voltage and the current. This shift is the result of energy being stored
and released in an inductor for example. To calculate the power consumed one
must consider this phase shift. We do so by using the following formula P=VI
cosine ø, where ø is the difference in phase angle between the
voltage and current. Cosine ø is called the power factor. For resistive
loads the power factor is equal to 1 because the phase angle equals 0. For
pure inductive loads the power factor is 0 because the phase angle is +90°.
propagation
The transmission of an electrical or electromagnetic signal through a medium
such as air or a conductor.
recognized
(UL recognized)
A device that is UL Recognized differs from a device that is UL Listed. A
Recognized device is expected to be installed within a larger assembly by
a manufacturer, not in the field, and this larger assembly is then expected
to be tested by UL. The UL Recognition then allows UL to skip testing of the
specific embedded Recognized component. UL Recognition has little value for
end users installing devices in the field.
rectifier
A device that allows current to flow in only one direction, such as a diode.
Used to convert, or rectify AC current into DC.
regulator
(voltage regulator)
A device, which uses a feedback loop to control the output of an alternator
or other source. By measuring the output voltage and controlling the alternator
field current, for example, the regulator is able to continuously adjust the
alternator output to the desired
voltage.
reserve capacity (battery)
RC is the number of minutes a new, fully charged battery at 80ºF will
sustain a discharge load of 25 amps to a cut-off voltage of 1.75 volts per
cell (10.5V on 12V battery). This battery rating measures more of a continuous
load on the battery.
resistance
The opposition to the flow of current in an electric circuit as defined by
Ohm's law. The unit of resistance is the ohm, symbol &, the Greek letter
Omega.
reverse polarity
Describes a situation where the neutral and hot wires of an AC system are
reversed. Most AC panels have an indicator to annunciate this condition, as
it can be very dangerous.
RMS (Root-mean-square)
Root-mean-square (rms) refers to the most common mathematical method of defining
the effective voltage or current of an AC wave.
To determine rms value, three mathematical operations are carried out on the
function representing the AC waveform:
(1) The square of the waveform function (usually a sine wave) is determined.
(2) The function resulting from step (1) is averaged over time.
(3) The square root of the function resulting from step (2) is found.
In a circuit whose impedance consists of a pure resistance, the
rms value of an AC wave is often called the effective value or DC-equivalent
value. For example, if an AC source of 100 volts rms is connected across a
resistor, and the resulting current causes 50 watts of heat to be dissipated
by the resistor, then 50 watts of heat will also be dissipated if a 100-volt
DC source is connected to the resistor.
For a sine wave, the rms value is 0.707 times the peak value, or 0.354 times
the peak-to-peak value. Household utility voltages are expressed in rms terms.
A so-called "117-volt" AC circuit has a voltage of about 165 volts
peak (pk), or 330 volts peak-to-peak (pk-pk).
sacrificial
anode
A less noble metal intentionally connected to form a galvanic cell with a
more noble metal for the purpose of protecting the more noble metal from corrosion.
Most commonly zinc.
safety
green (ground) wire
The non-current carrying conductor in a three wire 120V or four wire 240V
AC circuit, it provides a safe path for fault current. See also green ground
wire.
SAE
(Society of Automotive Engineers)
A organization which sets standards for various equipment used in the automotive
industry. Since much of the basic equipment used in the marine industry originates
in the automotive industry it can be a relevant specifications body for the
marine industry as well.
SAE
wire gauge
Wire sizes as specified by the SAE, specifically for stranded wire. Similar
to the AWG, see also AWG. The same gauge in SAE wire has a smaller conductor
than in AWG wire.
sealed
lead-acid see Gel Cell
self-limiting
A device whose ability to limit output power regardless of input power is
intrinsic to its design.
sheath
The ABYC uses this term when discussing the allowable length of a conductor
before it must have over current protection. The distance is extended if it
is in a sheath.
speed
see delay
Indicates how fast circuit protection devices react, specifically with respect
to over current protection and fuses.
stray
current corrosion
Corrosion that results when current from a battery or other external electrical
(DC) source causes a metal in contact with an electrolyte to become anodic
with respect to another metal in contact with the same electrolyte.
surge current see also continuous current
The pulse of current that is associated with the initial large current required
to start an electric motor, large resistive loads, and engine cranking.
shore
power
AC utility power that is available when plugged into an outlet that is supplied
from the main utility system.
short
circuit
A conductive path of zero resistance. Typically refers to an unintentional
connection between two conductors of opposite polarity. If a voltage is applied
to a short circuit the current
becomes very large and can start a fire, thus the need for short circuit,
or overcurrent, protection in the form of fuses or circuit breakers.
shunt
A shunt resistor is a precise, low Ohm resistor that is temperature stable.
It is used as a current "sensor" by using a millivolt meter to measure
the voltage drop across it. Large current shunts are commonly made of one
or more strips of manganin, a copper alloy capable of carrying high currents,
that are soldered between machined blocks of brass with connecting bolts.
Shunts are rated according to the number of Amps it is capable of carrying
and the millivotage which is generated
across the shunt when the rated current is being passed through it. Common
shunt ratings include 100A 100mV or 500A 50mv. The resistance can be calculated
by using Ohms Law, V=IR, 50mV=500A(R), therefore R=0.1mOhm, or
0.0001Ohm. This is a very small value of resistance; it must be in order to
minimize the power loss when large currents are flowing.
The shunt normally has two separate screws on to which the sense leads are
attached. It is important to realize that the integrity of these connections
are critical to accurate measurement and should not be used as current carrying
connections.
skin
effect
skin effect refers to the phenomena of conductors' propagating AC current
more efficiently on the conductors' surface than in its interior. This is
because AC voltage changes polarity 120 times per second (60 Hz). Voltage
signal penetration into the conductor interior takes a brief amount of time,
so the current propagation in the interior lags that of the exterior, resulting
in a longer period of propagation on the surface.
sine wave
A waveform that can be expressed as the graph of the equation y = sin x. The
utility AC power is a sine wave.
single
phase
The typical 120/240V AC system in the United States is a single phase system,
meaning that the current flow in the two conductors is in phase or that they
both cross zero at the same time.
slow
see delay
The speed with which a circuit element such as a fuse or circuit
breaker responds to an over-current condition.
slow
blow see also delay
A fuse that is a slow blow has a longer delay when subjected to over-current,
before it fails. Slow blow fuses are required for loads that have high starting
surges, like motors.
solenoid
(relay)
An electromechanical device that is used to switch large
currents. It consists of a coil of wire and a moving contact that
makes an electrical connection when the coil of wire is energized.
source
isolation (AC)
The arrangement of multiple AC power sources in such a manner that two AC
sources cannot be connected to the same circuit simultaneously.
source
selector
A switch or breaker configuration, which allows the user to pick which source
to have connected to the bus. Typically used in AC systems with multiple sources
such as shore power and one or more generators.
square
wave
An electrical waveform in which the current quickly goes from zero to its
peak value in a step fashion. This is typical of inexpensive inverters.
starting
bank
An arrangement of batteries that is designated for the function of engine
starting.
stray
current corrosion
Currents which may exist due to partial short circuits on one boat or on a
boat in an adjacent slip which can be conducted through the water and the
bonding system and cause deterioration of metallic devices.
storage
battery
An electrochemical device capable of storing energy and releasing it and then
able to be re-charged and repeat the process.
stray
current
Unwanted current flows which occur due to a partial short circuit.
sulfation
Sulfation is the
formation or deposit of lead sulfate on the surface and in the pores of the
active material of the batteries' lead plates. If the sulfation becomes excessive
and forms large crystals on the plates, the battery will not operate efficiently
and may not work at all. Common causes of battery sulfation are standing a
long time in a discharged condition, operating at excessive temperatures,
and prolonged under or over charging
surge
A large amount of current during the initial starting phase of a motor for
example.
surge
capacity
The measurement of the ability to withstand surge currents without damage.
An electro-mechanical device that is intended to open an electrical circuit
and thus turn a load or source on or off. switchboard see panel board
terminal
A connection point or device for an electrical circuit. A terminal strip is
a series of screws which may or may not be in common to which wires are connected.
Also refers to the connecting device which may be crimped on the end of a
wire to enable it to be connected to the circuit with a screw, such as a ring
terminal.
terminal
studs
A threaded bolt onto which ring terminals may be placed and then fastened
with a nut. Normally used for high current connections.
time-current
curve see also delay
A curve which depicts the relationship between the amount of current a fuse
or breaker can withstand with respect to time.
tin
plating
A plating of the element tin, which prevents corrosion. Commonly used to plate
copper components such as a power bus.
thermal
In a marine context thermal most commonly refers to a thermal circuit breaker,
which uses the thermal effect of excess current flow to create differential
expansion in a bi-metallic blade to open
a circuit.
toggle
see also pole
A switch which has a handle type actuator that can be placed in, at the most,
three positions.
transfer
switch, AC see selector switch, source isolation
An electrical relay or manual switch which selects an AC source alternative,
such as a generator, shore power, or inverter.
transformer
isolation see Isolation Transformer
trip
free
A circuit breaker designed to trip when subjected to a fault current, even
if the reset lever is held in the ON position.
ungrounded
conductor
Any conductor that is not connected to the Earth ground system
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 see also line loss
watt
The unit of power which for a DC circuit is equal to volts times amps
weatherproof
Constructed or protected so that exposure to the weather will not interfere
with successful operation in rain, spray, and splash
wire
sizing
The process of selecting the appropriate sized conductor for the amount of
current to be carried while considering the length of the circuit.
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 specific temperature.
withstand voltage
The maximum voltage level
that can be applied between circuits or components without causing a breakdown