The electrically conductive connection between the air-termination system and the earth-termination system is the down conductor system. The purpose of down-conductor systems is to safely transport intercepted lightning current to the earth-termination system without causing excessive temperature spikes that could harm the structure.
It must be mounted to ensure that the system is unharmed during the lightning current discharge. Multiple parallel currents run to create connections for conductive components of the structure. These currents can be straight, vertical and with no loops.
How to select a Down Conductor for Lightning Protection System?
a) You can decide by considering the perimeter and external edges of the roof (the projection on the ground surface).
b) They must be positioned such that they can disperse around the perimeter of the structure commencing at the corners.
c) The lengths between the various down conductors can vary depending on structural elements (e.g gates, precast components).
d) The corresponding lightning protection system class requires the total number of down conductors in every scenario. For each class of lightning protection system, the IEC 62305-3 (EN 62305-3) standard specifies typical distances between down conductors and ring conductors.
For each class of lightning protection system, the maximum temperature rise should be ΔT. A precise number of down conductors can be established by determining the separation distances. If the calculated separation distance cannot be maintained for the intended number of down conductors in a building, increasing the number of down conductors is one technique to achieve this requirement.
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Installation of Down Conductor for Lightning Protection System (LPS):
a) The down conductors must connect the air-termination conductors in a direct line.
b) They must be straight and vertical to provide the quickest direct connection to the earth possible.
c) Loops must be avoided, such as projecting eaves or structures or the distance between two down-conductor system points. The length of the down-conductor system between these points must meet the separation distance’s requirement.
d) The total length l = l1 + l2 + l3 computes the separation distance measured in s.
e) For aluminium, it must not be laid immediately (without a gap) under plaster, cement, or concrete, nor in the ground. If it has a PVC sheath, it can be put in mortar, plaster or concrete (if the sheath is not physically damaged and the insulation does not crack at low temperatures).
f) Conductors maintain the required separation distances between all doors and windows.
g) They must be linked such that the metal gutters intersect with the down conductor.
h) Even if the pipe is non-utilised as a down conductor, the base of metal downpipes must connect to the equipotential bonding or earth-termination system. The downpipe collects a portion of the lightning current since it is attached to the eaves gutter, through which it passes current that needs to pass via the earth termination system.
Natural Components of Down Conductor:
The number of down conductors placed individually can reduce when natural components of the structure are used.
As “natural components” of the down-conductor system, the following aspects of a structure can be used:
a) Metal installations, as long as the safe connection between the various parts is permanent and the size of the down conductors meet the minimal standards. The insulating material may also wrap these metal constructions.
b) If the seals or connected pipes in the flanges/couplings are non-metallic, conduits containing flammable or explosive materials as down conductors are prohibited. It is not electrically conductive since they are not connected.
Metal Skeleton: Ring conductors are not necessary if the metal frame of structures (with a steel skeleton or the interconnected reinforced steel) is employed as a down-conductor system, since additional ring conductors would not increase the current splitting.
Safe Interconnected Reinforcement: Existing structure reinforcement cannot be employed as a natural component of the down-conductor system unless the reinforcement can be safely coupled. External down conductors must be separate.
Parts for Precast: The terminal connectors for the reinforcement must be in the precast sections. All terminal connections on precast pieces must have an electrically conductive connection.
Facade elements, mounting channels, and metal substructures of facades can also be employed as a natural down-conductor system if:
1) The dimensions are within the range of down-conductor systems’ minimum requirements. The thickness of sheet metal must not be less than 0.5 mm.
2) In the case of metal facades, they must be interconnected by screws, rivets, or bridging connections to guarantee that the individual plates are securely attached.
3) To the earth & air-termination system, there must be a safe connection capable of carrying currents.
4) Metal plates can be utilised as a down-conductor system if not connected under the above criteria. But the substructure ensures that they are continually conductive from the air termination system to the earth-termination system.
Internal Down Conductor for Lightning Protection System (LPS):
If the structure’s edges (length and breadth) are 4x the distance between the down conductors, it might correspond to the lightning protection system’s class. That might lead to additional internal down conductors.
The internal down-conductor systems have a grid size of roughly 40 m x 40 m. They are for large constructions with flat roofs, such as production halls or distribution centres. In such circumstances, the ducts through the roof’s surface should be placed by a roofer, who is also responsible for ensuring that the roof is weatherproof.
When designing the internal lightning protection, pay attention to inputs to electrical equipment and the area of the down conductor.
Down Conductors for Courtyards Lightning Protection System (LPS):
Down-conductor systems must be installed in structures with enclosed courtyards with a circumference of more than 30 m.
Isolated External Down Conductors for Lightning Protection System (LPS):
A metal flag pole can be employed as an air-termination device for aesthetic purposes. The air-termination and down-conductor systems, as well as the structure, must maintain their separation distances. Each end of the cable to which the conductors are attached requires at least one down conductor if the air-termination system consists of one or more spanning wires or cables.
Axis based products for lightning protection system ensures safety and reliability for down conductors where the lightning rod is connected to the ground by at least two down conductors on opposite facades. The down conductors must be positioned outside the structure, away from electricity and gas lines. It must travel as straight as possible, using the quickest route to the ground and avoiding any sudden bends or lifts.
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