6.1 External LPS
The required level of protection (LPL I, II, III or IV) for the External Protection System shall be determined through the Risk Assessment which shall be conducted in terms of SANS 62305-2. Once the LPL is established the parameters for the external protection system are selected i.e. conductor sizes, down conductor spacing, rolling sphere radius, mesh size, protective angle etc.
– Air Termination System (ATS)
The function of the ATS is to prevent any direct lightning strikes from damaging the structure by intercepting the lightning strike, preventing penetration into the protected space. A correctly designed system will significantly reduce the risk of a direct strike to the structure. It is not possible to completely eliminate this risk.
An ATS can consist of the following components:
- Spanned wires and cables
- Conductors in conductor holders
It is important that the ATS covers corners and edges of a structure as these areas are most vulnerable to a direct strike. It is also important that any masts used are able to withstand the wind loading for the area in which it is installed.
– Down Conductor System (DCS)
The function of the DCS is to safely conduct the lightning current from the ATS to the ETS without damaging the building.
The important aspects of a DCS are:
- Several parallel current paths ie the more DCS the better
- The length of the DCS must be as short as possible (straight, vertical, no loops)
- Connections to conductive parts of the structure are made wherever possible
The maximum spacing between the down conductors is dependent on the Lightning Protection Level (LPL). The number of down conductors will also depend on the geometry (perimeter) of the structure. The down conductors should be placed such that there is a down conductor at each corner of the structure. The down conductors should then be spaced evenly around the perimeter in accordance with the LPL.
In the case of an isolated LPS the number and position of the DCS can vary significantly more than the above method.
– Earth Termination System (ETS)
The earth termination system is designed to safely dissipate the lightning current (lightning protection systems) or fault current safely into the ground.
The design of the Lightning Protection ETS is different to that of Power Frequency ETS, this is mainly due to the high impulse (dynamic) characteristic of Lightning.
6.2 Internal LPS
Sensitive electrical and electronic systems are becoming common place in modern buildings. These systems can be safety critical and therefore require permanent availability and reliability. A few examples are security systems, fire detection systems, life support systems in hospitals, telecommunications, building management systems etc.
These systems are also sensitive to temporary over voltages (surges) which are caused by both lightning discharge and switching operations on the electricity supply.
Internal LPSs consist of the following protection methods:
– Equipotential Bonding (EB)
Lightning equipotential bonding is the connection of all conductive elements of the building to the LPS and is carried out to prevent dangerous sparking inside the structure.
The typical conductive elements of a building are metal pipes (water, air conditioning etc), gas pipes, steel structures, lift mechanisms, ducts etc. The connection of these systems to the LPS is done to prevent potential differences which can result in hazardous touch potentials as well as damage to electrical / electronic systems.
– Separation Distance (’S’)
Roof mounted structures such as HVAC, telecommunication masts and CCTV camera systems present a high risk of introducing lightning currents to the inside of the building. This risk can result in the damage of equipment and loss of human life. In order to reduce this risk the roof mounted structures should be protected by an Isolated LPS. An Isolated LPS ensures that all conductors of the LPS are separated from any other conductive elements by the calculated separation distance.
6.3 Complete Lightning Protection System
The complete lightning protection system consist of both the internal LPS and the external LPS.
The design and installation of an external LPS only does not constitute a complete LPS.