Lightning protection zone concept

Lightning protection zones in buildings equipped with safety systems

Building management, telecommunication, control and safety systems are increasingly used in all areas of residential and functional buildings. These networked systems make the building intelligent and ensure its optimised use. Building owners and operators make high demands on the availability and reliability of these systems. An external lightning protection system protects persons and material assets in a building from fire, however, electrical and electronic systems are not protected against failure as a result of surges caused by a lightning discharge. A lightning protection zone concept in conformity with the IEC 62305-4 standard provides effective protection against surges caused by a lightning electromagnetic impulse (LEMP). According to this principle, the structure to be protected must be subdivided into inner lightning protection zones with different LEMP threat values. It is advisable to match the lightning protection zones and their LEMP threat values with the withstand capability of the relevant electronic system.

The above figure exemplarily shows the lightning protection zones of a fire alarm system according to the type of lightning threat.

Outer zones:

LPZ 0A: Zone in which the threat is due to direct lightning strikes and the undamped lightning electromagnetic field. Systems such as cables extending beyond the building may be subjected to the full lightning current.
LPZ 0B: Zone protected against direct lightning strikes, in which, however, the undamped lightning electromagnetic field is present. Systems such as alarm lights or sirens may be subjected to partial lightning currents.

Inner zones:

Inner zones are protected against direct lightning strikes and are subdivided into:
LPZ 1: Zone in which impulse currents are limited by current distribution and SPDs at the zone boundaries. Spatial shielding may attenuate the lightning electromagnetic field. Ring conductors with detectors are frequently installed in LPZ 1.
LPZ 2: Zone which, in comparison to LPZ 1, is additionally protected against impulse currents and the lightning electromagnetic field and is thus subjected to a lower interference.
LPZ 3: Zone which requires maximum protection against the effects of a lightning strike. Electronic systems such as fire control panels are frequently installed in LPZ 3. Surge arresters and shielding measures reduce impulse currents and electromagnetic fields to an acceptable level for the system technology.