Brochure/Catalogue

Surge protection concept
If a lightning protection system has been installed, or the
power supply is via overhead lines, or buildings or plants are
spread over a wide area and individual buildings are sited on
elevated ground or open areas, high-capacity Type I arresters
should always be employed.
2. Subdistribution
The surge voltage strength of the insulation is 4 kV from the
main distribution board up to and including subdistribution
boards. Owing to the co-ordinated use of arresters, Type II
surge arresters are used here and, if necessary, decoupled
from Type I arresters by means of coils. The use of
decoupling coils is only necessary when the Type I arresters
consist of one sparkover gap and the length of the line
between the Type I and Type II arresters is less than 10 m.
It is not necessary to decouple Weidmüller Type I and
Type II arresters. The pulse currents that occur here are no
longer that high because most of the energy has already
been absorbed by the Type I arresters. Nevertheless, the line
impedances give rise to high interference voltages which
must be limited to less than 4 kV by the Type II arresters.
Type II arresters based on varistors are normally installed in
the sub distribution board before the residual-current circuit-
breakers.
3. Terminals, consumers, sockets
The surge voltage strength of the insulation is 2.5 kV from
the subdistribution board to the electrical consumer. Surge
arresters in Type III are used for this purpose. Depending on
the application, they can be used as protective components
or in composite switching together with gas discharge
tubes, varistors, suppressor diodes and decoupling elements.
These arresters are best installed directly before the device
to be protected. This can be in a socket or trailing socket (on
extension lead) but also in the terminal or junction box of the
device itself.
To protect against permanent interference such as “ripples”
or “noise” caused by other systems, additional lter
circuits are available for the voltage supplies to devices.
The insulation of the electrical consumer itself has a surge
voltage strength of 1.5 kV.
Lightning arrester
Type I (B)
6 kV
Main distribution board/
Incoming power supply
Overvoltage arrester
Type II (C)
4 kV
Sub distribution board
Arrester
Type III (D)
2.5 kV
1.5 kV
Electrical consumer
Design surge voltage 300 V conductor-to-earth voltage
Wh
R
B
L1
L2
L3
N
PE
Principle for selecting arresters according to IEC 60664-1 (DIN VDE 0110-1)
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The basics of lightning and surge protection
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