## 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) |

Electrical Installation Calculations | Advanced |

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) |