92506E_Ver6.0.indd/2 Surge arresters Choosing surge arresters for: L V ne tworks In function of the site’s characteristics Choosing surge arresters: 2 examples of use installing surge arresters in a structure equipped with a lightning conductorinstalling surge arresters in a structure not equipped with a lightning conductor. b b E 9 1 0 0 7 Installation with lightning conductorThe presence of a lightning conductor on the building or in a 50 m radius can cause a direct lightning stroke generating a rise in the frame potential and that of the earthing system. Part of the lightning current rises in the electrical installation through the rod then the earth ba r. in order to protect the loads, a high flow capacity Type 1 PRF1 surge arrester (class 1 test) must then be installed at the incomer end of the switchboard that is capable of arcing and then conducting the lightning current towards a distant earth referenced at 0 V. Two technologies are available: air gap technology: this is the PRF1 range requiring systematic installation of another surge arrester (type 2) in cascade, so that the residual voltage at the terminals of the second surge arrester I max = 40 kA (PRD40, PF40) is compatible with the impulse withstand voltage of the equipment to be protected (U impulse < 1.5 kV) technology with varistor: this is the PRD1 draw-out surge arrester range. Installation of another surge arrester (type 2) is not required. if the loads to be protected are located more than 30 m away from the incoming protection, a secondary protection surge arrester I max 8 kA (PRD8, PF8) will be installed as close as possible to the loads Type 1 (class 1 test) or Type 2 (class 2 test) surge arresters meet the standard EN 61-643-11 (IEC 61643-11). Type 1 protection with PRF1 b b v v b b D B 1 0 7 9 2 0 Type 1 protection with PRD1 D B 1 0 7 9 0 3 Services Practical services
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In function of the site’s characteristics Choosing surge arresters: 2 examples of useinstalling surge arresters in a structure equipped with a lightning conductor
installing surge arresters in a structure not equipped with a lightning conductor.
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Installation with lightning conductor The presence of a lightning conductor on the building or in a 50 m radius can cause
a direct lightning stroke generating a rise in the frame potential and that of the
earthing system. Part of the lightning current rises in the electrical installation through
the rod then the earth bar.
in order to protect the loads, a high flow capacity Type 1 PRF1 surge arrester (class 1
test) must then be installed at the incomer end of the switchboard that is capable of arcing
and then conducting the lightning current towards a distant earth referenced at 0 V.
Two technologies are available:
air gap technology: this is the PRF1 range requiring systematic installation of
another surge arrester (type 2) in cascade, so that the residual voltage at the terminals
of the second surge arrester I max = 40 kA (PRD40, PF40) is compatible with the impulse
withstand voltage of the equipment to be protected (U impulse < 1.5 kV)
technology with varistor: this is the PRD1 draw-out surge arrester range.Installation of another surge arrester (type 2) is not required.
if the loads to be protected are located more than 30 m away from the incoming
protection, a secondary protection surge arrester I max 8 kA (PRD8, PF8) will be installed
as close as possible to the loads
Type 1 (class 1 test) or Type 2 (class 2 test) surge arresters meet the standard
Permanent operating full withstand voltage Uc as in the IEC 60364-5-534 standardEarthing systems TT TN-S TN-C IT
Uc value for common mode(protection between liveconductors and earth)
u 1.1 Uo u 1.1 Uo u 1.1 Uo u 1.732 Uo
Uc value for differential mode(protection between phase andneutral)
u 1.1 Uo u 1.1 Uo u 1.1 Uo
Uo: simple network voltage between phase and neutral Uc: full voltage under permanent operating conditions.
Note: Rated impulse withstand voltage is an impulse withstand voltage assigned by the manufacturer to the equipment or to a part of it, characterizing the speci fi ed
capability of its insulation against overvoltages (in accordance with 1.3.9.2 of IEC 60664.1).
Type 1 surge arresters (class 1 test)PRF1 are dimensioned to conduct direct lightning currents with a 10/350 wave
formPRF1 are surge arresters that use “encapsulated air-filled spark gap “ type
technology without arc device
when the lightning current flows in the PRF1 surge arrester, a follow current (If) is
created. If the value of current Ifi is greater than the prospective short-circuit current
at the installation point, the PRF1 surge arrester discharges by itself, without the help
of the associated protective device.
Otherwise, the protective device may trip. An OF indication auxiliary associated with
the protective device should be provided to warn the user that loads are no longer
protected as long as the protective device is not reset (see the “indication” section).
the PRF1 Master surge arrester uses an “air spark gap” type technology with
electronic arcing.
Its main feature is its high level of protection and its good capacity to extinguish the
25 kA follow current without tripping the associated disconnection device.The extinction of the electrical arc is facilitated by sheet-metal elements that dividethe latter into several partial arcs. This technology increases the reliability of the
operation and the availability of the protected installation.
Type 2 surge arresters (class 2 test)these surge arresters use “varistor” type technology or “varistor + gas-filled spark
gap” technologythey are dimensioned to conduct indirect lightning currents with an 8/20 wave form.
Choosing the disconnection device After having chosen the surge arrester(s) needed to protect the installation, the
appropriate disconnection circuit-breaker is to be chosen from the opposite table:
its breaking capacity must be compatible with the installation’s breaking capacity
each live conductor must be protected example: a 1P+N surge arrester must be
combined with a 2P disconnection device (2 protected poles).
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Type 1 surge arrestersType of surge arrester Disconnection device
PRF1 D125 125 A curve Dor fuse NH type gG (gL) 125 A
PRF1 Master NS160N TM160D or fuse NH type gG (gL) 160 A
PRD1 C120
Type 2 surge arrestersMax. lightning discharge current Disconnection circuit-breaker
Rating Curve
65 kA 50 A C
40 kA 40 A C
20 kA 25 A C
8 kA 20 A C
Coordination between
Type 1 surge arresters (class 1 test) and
Type 2 surge arresters (class 2 test)To guarantee optimum protection of loads against direct effects (10/350 wave form)
and surges (8/20 wave form), induced or conducted, Type 1 and Type 2 surge
arresters must be installed in cascade.
There are 2 cases:
the Type 1 and Type 2 surge arresters are installed in the same switchboard:
the Type 1 surge arrester with air spark gap technology has the same steady state
voltage (Uc) as the Type 2 surge arrester with varistors
the Type 1 surge arrester Neutral/PE pole is common to both surge arresters
the Type 1 and Type 2 surge arresters are installed in two separate switchboards:
The Type 1 surge arrester has the same steady state voltage (Uc) as the Type 2
surge arrester.
In both cases, each surge arrester is associated with its protective device.
An OF opening indication auxiliary for the protection devices is
In installations fitted out with a general earth leakage protection, it is preferable to
place the surge arrester upstream from this protection.However, certain power distributors do not allow intervention at this distribution level
(this is for instance the case for LV subscribers in France).
It is therefore necessary to plan a selective device of the s type, or with delayed
tripping, so that when the current runs off to the earth through the surge arrester, it
does not produce nuisance tripping of the incoming circuit-breaker.
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The best way to guarantee the continuity of supply of priority circuits, while ensuring
safety in the case of atmospheric disturbances is to combine:
a surge arrester that can protect sensitive loads against atmospheric overvoltagesa circuit-breaker with an upstream earth leakage protection device of 300/500 mA
selective, to ensure total earth leakage discrimination
a residual current device of 30 mA s type placed downstream is insensitive to this
type of disturbance.
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Another solution can be foreseen: use a circuit-breaker (not earth leakage) at the
incoming end of the installation followed by a residual current circuit-breaker. The
surge arrester is to be connected between the two devices (see below).
Careful, the link L must be class II.
Choice depending on the communication
networkType of network Series PRC PRI 12…48 V PRI 6 V
Telecommunication
Digital 300 Hz RTC
Numeris access T0
Specialised 24 V line
Specialised modem line base band 64 kbit/s
MIC line and access T2
Computer
Current loop 200 V
Current loop 12…48 V
RS 232 (12 V)
RS 485 (12 V)
Current loop 6 V
RS 422 (6 V)
RS 423 (6 V)
Supply 12/48 V
Fire safety centralising equipment,ELV load, intrusion centralising