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tÉlÉcharger 18th edition wiring regulations pdf


IET Wiring regulations
BS 7671 18th edition
Transient overvoltage protection
4
I E T W I R I N G R E G U L AT I O N S B S 7 6 7 1 1 8 T H E D I T I O N

The IET Wiring Regulations require
all new electrical system designs
and installations, as well as
alterations and additions to existing
installations, to be assessed against
transient overvoltage risk and,
where necessary, protected using
appropriate surge protection
measures (in the form of
Surge Protection Devices SPDs).
T R A N S I E N T O V E R V O LTA G E P R OT E C T I O N - I N T R O D U C T I O N
3

Transient overvoltage protection
Introduction
Based on the IEC 60364 series, the 18th Edition of
BS 7671 Wiring regulations covers the electrical installation
of buildings including the use of surge protection.
The 18th Edition of BS 7671 applies to the design,
erection and verification of electrical installations,
and also to additions and alterations to existing
installations. Existing installations that have
been installed in accordance with earlier editions
of BS 7671 may not comply with the 18th edition
in every respect. This does not necessarily
mean that they are unsafe for continued use or
require upgrading.
A key update in the 18th Edition relates to
Sections 443 and 534, which concern protection of
electrical and electronic systems against transient
overvoltages, either as a result of atmospheric
origin (lightning) or electrical switching events.
Essentially, the 18th Edition requires all new
electrical system designs and installations,
as well as alterations and additions to existing
installations, to be assessed against transient
overvoltage risk and, where necessary, protected
using appropriate protection measures
(in the form of SPDs).
Within BS 7671:
• Section 443 defines the criteria for risk
assessment against transient overvoltages,
considering the supply to the structure,
risk factors and rated impulse voltages
of equipment
• Section 534 details the selection and installation
of SPDs for effective transient overvoltage
protection, including SPD Type, performance
and co-ordination
Readers of this guide should be mindful of the
need to protect all incoming metallic service
lines against the risk of transient overvoltages.
BS 7671 provides focussed guidance for the
assessment and protection of electrical
and electronic equipment intended to be
installed on AC mains power supplies.
In order to observe the Ligntning Protection Zone LPZ
concept within BS 7671 and BS EN 62305, all other
incoming metallic service lines, such as data, signal
and telecommunications lines, are also a potential
route through which transient overvoltages to
damage equipment. As such all such lines will require
appropriate SPDs.
BS 7671 clearly points the reader back to BS EN 62305
and BS EN 61643 for specific guidance. This is
covered extensively in the Furse guide to BS EN 62305
Protection Against Lightning.
Data/
Telecom
Data/
Telecom
Power
Power
IMPORTANT:
Equipment is ONLY
protected against
transient overvoltages if
all incoming / outgoing
mains and data lines
have protection fitted.
I E T W I R I N G R E G U L AT I O N S B S 7 6 7 1 1 8 T H E D I T I O N
4

Transient overvoltage protection
Safeguarding your electrical systems
DAMAGE
> 1.5 kV
(L-PE/N-PE)
DAMAGE
Degradation
Safe
Operating
Area