Glossaire
CAPTURE POINT
Also referred to as the strike point. This is a 30 to 50 cm high metal rod, with a minimum diameter of 18mm and a tapered point.
CORONA EFFECT (CORONA DISCHARGE)
The corona effect is the local electrical phenomenon that occurs around an electrode with a low curvature radius when it is subjected to a high voltage. It is caused by successive electron avalanches that result in the ionization of air following high amplification of the electric field around this electrode. The electric currents involved in this type of discharge are well below 1mA.
DANGEROUS SPARKING
An electric arc produced by a lightning current within the volume to be protected.
DOWN-CONDUCTOR
Part of the external lightning protection installation designed to conduct the lightning current from the E.S.E.lightning conductor to the earth termination system.
EARLY STREAMER EMISSION LIGHTNING CONDUCTOR (PDA)
Standard lightning rod which, when fitted with an electric or electronic system to generate early streamer emissions (advanced initiation of the rising pre-discharge), has better performance when compared to a standard lightning rod in the same conditions. The method for calculating the protection radius of an early streamer emission device is described in NFC 17-102.
EARTH ROD
A part or group of parts of the earth termination system which provides direct electrical contact with the earth and disperses the lightning current to earth.
EARTH TERMINATION SYSTEM
A conductive part or a group of conductive parts in intimate contact with and providing an electrical connection with earth.
EARTH TERMINATION SYSTEM RESISTANCE
Resistance between the test joint and earth: it equals the quotient of potential increase, measured at the test joint with respect to an infinitely remote reference, and of the applied current to the earth electrode.
EQUIPOTENTIAL BONDING
An electrical connection putting ground conductors and conductive parts at the same potential or a substantially equal potential.
EQUIPOTENTIAL CONDUCTOR
A conductor providing for equipotential bonding.
EQUIVALENT COLLECTION AREA OF A STRUCTURE AE
A flat ground surface subjected to the same number of lightning flashes as the structure under consideration.
IMPACT POINT
Point where a lightning strike hits the ground, a structure or a lightning protection installation.
IMPEDANCE
The characteristic impedance is the main parameter for defining electrical signal propagation along a line. This signal is always a pair of two mobile waves, voltage u(t) and current i(t), that are rigidly linked and which propagate at the same speed. The characteristic impedance Zc (also referred to as "wave impedance") is the constant ratio between these two values, i.e. Zc = u(t) / i(t). (Source: UTE/SEE "Guide de la protection", June 2000 edition).
INITIATION ADVANCE (ΔT)
The initiation advance is the difference between the initiation time of an early streamer emission device (PDA) and the initiation time of a standard lightning rod (PTS) when compared in the same conditions. This is expressed in µs.
INTERCONNECTED REINFORCING STEEL
Natural components within a structure which provide an electrical path resistance smaller than 0.01 Ωand can be used as down-conductors.
INTERNAL LIGHTNING PROTECTION INSTALLATION (ILPI)
An internal lightning protection installation consists of all the devices and measures reducing the electromagnetic effects of lightning current within the volume to be protected.
IONIZATION
Series of physical processes by which ions are created. An ion is an atom or group of atoms that have gained (negative ion) or lost (positive ion), by electrolysis or through radiation, one or more electrons.
LIGHTNING ROD
Lightning rods (sometimes referred to as Franklin rods) have a practical height of 2 to 6 metres and a tapered point. They may be made up of one or more like material components, provided that electrical continuity is guaranteed (NF C 17-100).
LIGHTNING STRIKE
The lightning strike is the phenomenon that occurs when a thunder cloud is connected via rising and falling tracers to the ground. It occurs after two tracers have joined. All the charge contained in the thunder cloud rushes into the ionized channel formed by the two tracers and produces an electric discharge.
LIGHTNING FLASH TO EARTH
An electrical discharge of atmospheric origin between cloud and earth, consisting of one or more current impulses (return strokes).
LIGHTNING FLASH DENSITY NG
Yearly number of lightning flashes per km².
LIGHTNING PROTECTION SYSTEM (LPS)
The complete system used to protect structures and open areas against the effects of lightning. It consists of an external lightning protection installation and of an internal lightning protection installation, if any.
LEADER INITIATION PROCESS
Physical phenomenon between the inception of the first corona and the continuous propagation of an upward leader.
NATURAL COMPONENT
A conductive part located outside the structure, sunk in the walls, or situated inside a structure and which may be used to replace all or part of a down-conductor or as a supplement to an ELPI.
PROTECTED VOLUME
Volume of influence of the early streamer emission lightning conductor within which the early streamer emission lightning conductor is the striking point.
PROTECTION LEVEL
The protection level corresponds to the statistical effectiveness of the protection expressed as the probability of capturing a lightning strike according to its intensity. As a minimum, the protection captures all lightning strikes of greater intensity than that under consideration.
Effectiveness (E)
in % |
Intensity of lightning current (in kA) |
Protection level (Np) nf c 17-100 |
Protection level (Np) NF C 17-102 |
E > 98 |
- |
1 + additional measurements |
1 + additional measurements |
95 < e ≤ 98 |
2,8 |
1 |
1 |
90 < e ≤ 95 |
5,2 |
2 |
2 |
80 < e ≤ 90 |
9,5 |
3 |
2 |
E < 80 |
14,7 |
4 |
3 |
RETURN STROKE DENSITY NA
Yearly number of return strokes per km². A lightning stroke consists, in average, of several return strokes.
SAFETY DISTANCE (S)
The minimum distance for which no dangerous spark can be produced.
STREAMER
The streamer is the filament type electrical discharge that develops over distances as great as several tens of centimetres. It is produced by successive electron avalanches that create a weakly ionized channel. This type of discharge occurs when the electric field is greater than the air ionization field over a distance that is at least as long as the electron avalanche. This field value is much higher than that needed for a corona discharge. The streamer discharge can carry currents ranging from several mA to several tens of mA.
STRIKING POINT
A point where a lightning stroke contacts the earth, a structure, or a lightning protection system.
SURGE PROTECTIVE DEVICE (S.P.D.)
A device designed to limit transient surge voltages and to provide a path for the current waves. It contains at least one non linear component.
TAUGHT WIRE LIGHTNING CONDUCTOR
This system is made up of one or more wire conductors stretched above the installations that are to be protected. Comment: in practice, lightning rod systems act more or less as a cage due to the presence of roof and down conductors: this can contribute in protecting the volume they enclose. Inversely, when a mesh cage system is fitted with capture points, these have a slightly preferential attraction of lightning.
TRACER
The tracer is the path followed by successive streamer discharges that create an ionized channel over greater distances (up to 50m). The electric currents involved in this type of discharge vary between 1 Amp and several tens of Amps.
TEST CLAMP
A device used to disconnect the earth termination system from the remainder of the system.
TRANSIENT SURGE VOLTAGE OF ATMOSPHERIC ORIGIN
Overvoltage lasting a few milliseconds only, oscillatory or not, usually strongly damped.