BASIC
ELECTRIC TERMS AND
Alternating Current (AC)
An
electric current that reverses its direction many times a second at regular
intervals.
Ampere
(A)
A unit of
measure for the intensity of an electric current flowing in a circuit. One
ampere is equal to a current flow of one coulomb per second.
Apparent
Power
Measured in
volt-ampers (VA). Apparent power is the product of the rms voltage and the rms
current.
Capacitance
The ability of
a body to store an electrical charge. Measured in farads as the ratio of the
electric charge of the object (Q, measured in coulombs) to the voltage across
the object (V, measured in volts).
Circuit
A closed path
in which electrons from a voltage or current source flow. Circuits can be in
series, parallel, or in any combination of the two.
Circuit
Breaker
An automatic
device for stopping the flow of current in an electric circuit. To restore
service, the circuit breaker must be reset (closed) after correcting the cause
of the overload or failure.
Conductor
Any material
where electric current can flow freely. Conductive materials, such as metals,
have a relatively low resistance. Copper and aluminum wire are the most common
conductors.
Current
(I)
The flow of an
electric charge through a conductor. An electric current can be compared to the
flow of water in a pipe. Measured in amperes.
Demand
The average
value of power or related quantity over a specified period of time.
Diode
A
semiconductor device with two terminals, typically allowing the flow of current
in one direction only. Diodes allow current to flow when the anode is positive
in relation to the cathode.
Direct
Current (DC)
An electric
current that flows in only one direction.
Farad
A unit of
measure for capacitance. One farad is equal to one coulomb per volt.
Frequency
The number of
cycles per second. Measured in Hertz. If a current completes one cycle per
second, then the frequency is 1 Hz; 60 cycles per second equals 60 Hz.
Fuse
A circuit
interrupting device consisting of a strip of wire that melts and breaks an
electric circuit if the current exceeds a safe level. To restore service, the
fuse must be replaced using a similar fuse with the same size and rating after
correcting the cause of failure.
Ground
The reference
point in an electrical circuit from which voltages are measured, a common
return path for electric current, or a direct physical connection to the Earth.
Ground
Fault Circuit Interrupters (GFCI)
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.
Henry
A unit of
measure for inductance. If the rate of change of current in a circuit is one
ampere per second and the resulting electromotive force is one volt, then the
inductance of the circuit is one henry.
Hertz
A unit of
measure for frequency. Replacing the earlier term of cycle per second (cps).
Inductance
The property
of a conductor by which a change in current flowing through it induces
(creates) a voltage (electromotive force) in both the conductor itself
(self-inductance) and in any nearby conductors (mutual inductance). Measured in
henry (H).
Insulator
Any material
where electric current does not flow freely. Insulation materials, such as
glass, rubber, air, and many plastics have a relatively high resistance.
Insulators protect equipment and life from electric shock.
Inverter
An apparatus
that converts direct current into alternating current.
Kilowatt-hour
(kWh)
The product of
power in kW and time in hours. Equal to 1000 Watt-hours. For example, if a 100W
light bulb is used for 4 hours, 0.4kWhs of energy will be used (100W x 1kW /
1000 Watts x 4 hours). Electrical energy is sold in units of kWh.
Kilowatt-hour
Meter
A device used
to measure electrical energy use.
Kilowatt
(kW)
Equal to 1000
watts.
Load
Anything which
consumes electrical energy, such as lights, transformers, heaters and electric
motors.
Ohm
(Ω) A unit of
measure of resistance. One ohm is equivalent to the resistance in a circuit
transmitting a current of one ampere when subjected to a potential difference
of one volt.
Ohm's
Law
The
mathematical equation that explains the relationship between current, voltage,
and resistance (V=IR).
Parallel
Circuit
A circuit in
which there are multiple paths for electricity to flow. Each load connected in
a separate path receives the full circuit voltage, and the total circuit
current is equal to the sum of the individual branch currents.
Power
The rate at
which electrical energy is transferred by an electric circuit. Measured in
Watts.
Power
Factor
The ratio of
the actual electrical power dissipated by an AC circuit to the product of the
r.m.s. values of current and voltage. The difference between the two is caused
by reactance in the circuit and represents power that does no useful work.
Reactive
Power
The portion of
electricity that establishes and sustains the electric and magnetic fields of
AC equipment. Exists in an AC circuit when the current and voltage are not in
phase. Measured in VARS.
Rectifier
An electrical
device that converts an alternating current into a direct one by allowing a
current to flow through it in one direction only.
Resistance
The opposition
to the passage of an electric current. Electrical resistance can be compared to
the friction experienced by water when flowing through a pipe. Measured in
ohms.
Semiconductor
A solid
substance that has a conductivity between that of an insulator and that of most
metals, either due to the addition of an impurity or because of temperature
effects. Devices made of semiconductors, notably silicon, are essential
components of most electronic circuits.
Series
Circuit
A circuit in
which there is only one path for electricity to flow. All of the current in the
circuit must flow through all of the loads.
Service
The conductors
and equipment used to deliver energy from the electrical supply system to the
system being served.
Transistor
A
semiconductor device with three connections, capable of amplification in
addition to rectification.
True
Power
Measured in
Watts. The power manifested in tangible form such as electromagnetic radiation,
acoustic waves, or mechanical phenomena. In a direct current (DC) circuit, or
in an alternating current (AC) circuit whose impedance is a pure resistance,
the voltage and current are in phase.
VARS
A unit of
measure of reactive power. Vars may be considered as either the imaginary part
of apparent power, or the power flowing into a reactive load, where voltage and
current are specified in volts and amperes.
Volt-Ampere
(VA)
A unit of
measure of apparent power. It is the product of the rms voltage and the rms
current.
Volt
(V)
A unit measure
of voltage. One volt is equal to the difference of potential that would drive
one ampere of current against one ohm resistance.
Voltage
An
electromotive force or "pressure" that causes electrons to flow and
can be compared to water pressure which causes water to flow in a pipe.
Measured in volts.
Watt-hour
(Wh)
A unit of
electrical energy equivalent to a power consumption of one watt for one hour.
Watt
(W)
A unit of
electrical power. One watt is equivalent to one joule per second, corresponding
to the power in an electric circuit in which the potential difference is one
volt and the current one ampere.
