E — Dictionary of Quarrying Terms

EDM: abbr. see ‘electronic distance measurement’.

EIA: abbr. see. ‘environmental impact assessment’.

emf: abbr. see ‘electromotive force’.

earth electrode: A conductive part or group of parts in intimate contact with, and providing an electrical connection with, earth.

earth-fault current: A current that flows from phase conductors to earth or protective conductors etc from the point of an insulation breakdown.

earth-fault protection: A system of protection designed to cause the supply to an electrical circuit or system to be interrupted automatically when the leakage current to earth exceeds a predetermined value.

earth-leakage protection: see ‘earth-fault protection’.

earth testing: Tests to ensure that the resistance between the earth electrodes (ie earth plates, rods etc) and the general mass of earth does not exceed a prescribed value.

earth-leakage circuit-breaker: A device which disconnects the electricity supply if the voltage on non-current-carrying metalwork or the out-of-balance current in the supply due to leakage exceeds a predetermined value.

earthing conductor: A protective conductor connecting the main earthing terminal or main earthing bar to the earth electrode. Also used to describe an earth wire bonded from the metal work of an isolating switch (for example) to the cable armouring feeding it.

easement: A liability attaching to land, whereby some person other than the owner has certain clearly defined rights over it and in perpetuity. Alternatively, a right over land granted in perpetuity by the owners to some person for a specific purpose, eg passage, laying of mains drainage etc.

easting: see ‘departure’.

eccentric: Displaced with reference to a centre, eg the eccentric section of the shaft generating the motion of a four-bearing screen.

eddy current: In most cases unwanted currents generated by a magnetically induced electromotive force in a closed conductive path, such as the core of an electric machine, resulting in a waste of energy.

effective value: The root-mean-square value of an alternating current or voltage.

efficiency: 1 The ratio of useful output energy to input energy. 2 The efficiency of a simple machine is defined as the ratio of the force ratio to the movement ratio. See also ‘screening efficiency’.

elastic limit: The stress level above which a material remains permanently deformed when the stress is removed.

electromagnet: A current-carrying coil with a soft iron core, which has appreciable magnetic effect only when there is a flow of current.

electromagnetic induction: The production of an induced voltage in a circuit by means of the magnetic flux cutting the circuit. In order for an induced current to flow in a closed circuit the conductors and the magnetic field must move relative to each other.

electromagnetic screen: A screen to which is attached an electrically operated vibrator unit consisting of an armature and a stator connected to a halfwave rectified single-phase ac supply, which imparts a linear motion, usually of high frequency and low amplitude, to the screen.

electromotive force: The voltage applied to an electrical circuit which causes current to flow.

electronic distance measurement: A very accurate method of measuring distance by means of an electronic device. Most EDM instruments are operated by infra-red light or laser, with the beam being directed at a target which may be some kilometres away, and give a direct reading with an accuracy of 1 in 10000 or better.

electrostatic precipitator: An apparatus for removing dust from dust-laden air by creating electric charges on the dust particles, causing them to be attracted to a collecting plate.

element: In relation to time study, a distinct part of an operation selected for convenience of observation, measurement and analysis. BS 42003.

elevating scraper: A self-loading bowl scraper able to operate without the help of a pusher dozer except in very difficult conditions. It is fitted with an elevating conveyor with flights at regular intervals which, as the scraper moves forward, carry the material sliced off from the ground up into the bowl.

elevation: 1 A view of a component or assembly drawn in projection on a vertical plane, eg an end elevation. 2 The height of a point above sea level.

elevator: see ‘bucket elevator’.

elutriation: Process of dividing fine particles into size fractions according to their rate of fall through an upward current of water.

eluvial deposit: Rocks which have disintegrated through natural causes but which, unlike alluvial material which is transported away by water, have remained in situ.

empirical formula: A formula based on experience or the results of experiments, not deduced from theoretical considerations.

emulsion: 1 Bitumen emulsions, in which the bitumen is dispersed in water, through the use of emulsifying agents, as small globules permitting use at lower temperatures. 2 Explosive emulsions are mixtures of fuel and oxidizers (mainly nitrates) in a ratio of approximately 1:10, which have good water resistant properties and chemical stability. Emulsion/ANFO blends can be used to suit particular circumstances.

energy: The capacity to do work. Energy is expended when work is done. Unit: joule (J). Forms of energy include: mechanical, electrical, thermal, chemical etc.

energy factor: The amount of explosive energy required to break a unit volume of rock (MJ/m³) which may be used as a blast design criterion.

environmental impact assessment: Study of the potential environmental benefits and disbenefits arising from a development, usually conducted before a planning application is submitted.

Eocene: An epoch of the Tertiary period between 54 and 38 million years ago.

epicyclic gear: A system of gears in which one or more gear wheels travel round the inside or outside of another gear wheel, the axis of which is fixed.

equipotential bonding: Electrical connection putting various exposed conductive parts and extraneous conductive parts at a substantially equal potential.

equity: The shares of a company which do not bear fixed interest, ie the ordinary shares.

equivalent continuous sound level: The constant sound intensity level which in the course of continuous exposure for 8h would result in the same energy dosage as that due to the actual exposure. abbr. Leq.

erosion: The wearing away of parts of the Earth’s surface by the action of natural agents such as ice, water and wind.

evaporites: Rocks, such as anhydrite, rock salt, potash, salt etc, formed by evaporation of lakes or seas.

excavator: Self-propelled crawler or wheeled machine with an upper structure capable of rotation, which excavates, swings and discharges material by the action of a bucket fitted to the boom and arm, or telescoping boom, without moving the chassis or undercarriage during any part of the working cycle of the machine.

excitation time: The minimum time for which an electric current must flow in the fusehead of a detonator to ensure its ignition.

expanded metal: A metal network made by stamping and stretching sheet metal to form an open mesh. Used as reinforcement in concrete, in the manufacture of safety guards for machines etc.

exploder: A device designed specifically for producing an electric current for firing detonators. All exploders used in quarries must have a removable handle or key.

explosives store: Premises registered in accordance with section 21 of the Explosives Act 1875; a magazine licensed in accordance with sections 6 to 8 or a store licensed in accordance with section 15 of the 1875 Act.

explosives strengths: see ‘bulk strength’ and ‘weight strength’.

explosives supervisor: the appointed person in overall, day-to-day charge of work with explosives who must have successfully completed a course of training.

exposed aggregate: A decorative concrete finish in which the mortar is removed to expose the coarse particles at the surface.

extrapolation: The continuance of the line of a graph beyond the points for which values are available, in order to estimate values beyond the range of those points.

extrusion: The process of producing rods, tubes and various solid and hollow sections, by forcing suitable metals and plastic materials through a die.