 ## Glossary of terms

Term Meaning
a.c. Alternating current
Area Extent of a surface
BS 7671 British Standard for electrical wiring regulations
Capacitive reactance The effect on a current ﬂow due to the reactance of a capacitor
Circle Perfectly round ﬁgure
Circuit breaker A device installed into a circuit to automatically break a circuit in the event of a fault or overload and which can be reset
Circuit Assembly of electrical equipment which is supplied from the same origin and protected from overcurrent by a protective device
Circumference Distance around a circle
Conductor Material used for carrying current
Coulomb Quantity of electrons
Correction factor A factor used to allow for different environmental conditions of installed cables
C.S.A. Cross-sectional area Current
Cycle Passage of an AC waveform through 360◦
Cylinder Solid or hollow, roller-shaped body
d.c. Direct current
Dimension Measurement
Earth fault current The current which ﬂows between the earth conductor and live conductors in a circuit
Earth fault loop impedance Resistance of the conductors in which the current will ﬂow in the event of an earth fault. This value includes the supply cable, supply transformer and the circuit cable up to the point of the fault
Efﬁciency The ratio of output and input power Energy
E.M.F. Electromotive force in volts
Frequency Number of complete cycles per second of an alternating wave form
Fuse A device installed in a circuit which melts to break the ﬂow of current in a circuit
Force Pull of gravity acting on a mass
Hertz Measurement of frequency
Impedance Resistance to the ﬂow of current in an AC circuit
Impedance triangle Drawing used to calculate impedance in an AC circuit
Internal resistance Resistance within a cell or cells Kilogram
kW True power (× 1000)
kVA Apparent power (× 1000) kVAr
Load The current drawn by electrical equipment connected to an electrical circuit
Mutual induction Effect of the magnetic ﬁeld around a conductor on another conductor
Magnetic ﬂux Quantity of magnetism measured in Webers
Magnetic ﬂux density Is the density of ﬂux measured in Webers per metre squared or Tesla
Newton Pull of gravity (measurement of force)
On-Site Guide Publication by the IEE containing information on electrical installation
Ohm Unit of resistance
Overload current An overcurrent ﬂowing in a circuit which is electrically sound
Percentage efﬁciency The ratio of input and output power multiplied by 100
Power Energy used doing work
Pressure Continuous force
Primary winding Winding of transformer which is connected to a supply
Perimeter Outer edge
Phasor Drawing used to calculate electrical values
Potential difference Voltage difference between conductive parts Prospective short circuit current
Prospective fault current The highest current which could ﬂow in a circuit due to a fault
Protective device A device inserted into a circuit to protect the cables from overcurrent or fault currents
Resistor Component which resists the ﬂow of electricity
Resistance Opposition to the ﬂow of current
Resistivity Property of a material which affects its ability to conduct
Rectangle Four-sided ﬁgure with right angles
Space factor Amount of usable space in an enclosure
Secondary winding Winding of transformer which is connected to a load
Self-induction Effect of a magnetic ﬁeld in a conductor Series
Thermoplastic Cable insulation which becomes soft when heated and remains ﬂexible when cooled down
Transpose Change order to calculate a value
Triangle Three-sided object
Thermosetting Cable insulation which becomes soft when heated and is rigid when cooled down
Transformer A device which uses electromagnetism to convert AC current from one voltage to another
Voltage drop Amount of voltage lost due to a resistance
Volume Space occupied by a mass
Wattmeter Instrument used to measure true power
Waveform The shape of an electrical signal
Work Energy used moving a load (given in Newton metres or joules)