Basic of External Lightning Protection System (LPS)-(Part-4)

October 1, 2024 Leave a comment

Material Combinations and Dimensions

  • Required to use galvanically compatible metals in lightning protection system components and surface materials on which the components are mounted. For example, do not connect copper to aluminum.
  • Do not use together metals that are not galvanically compatible. Bad matching accelerates their corrosion in the presence of moisture.
  • With aluminum conductors, use only connection devices designed for aluminum. Make sure to use the right fastening torque.

 Different Contact Material

Material

Suitable Contact Material

Copper

 Nickel /Brass / Tin / Lead / Stainless steel / Monel (nickel–copper alloy)
Aluminum

Magnesium / Zinc / Galvanized steel / Stainless steel / Lead / Wrought iron / Galvalume (an aluminum-coated sheet steel product)

LPS Material

LPS Materials and Conditions of Use

Table-5 (IEC 62305-3)
Material Use Corrosion
In Open Air In Earth In Concrete Resistance Increased by May be destroyed by Galvanic Coupling with
Copper Solid Solid Solid Good in many environments Sulphur compounds –
Stranded Stranded Stranded – Organic materials –
– As coating As coating – – –
Hot galvanized steel123 Solid Solid Solid Acceptable in air, in concrete, and in benign soil High chlorides content Copper
Stranded 4 – Stranded 4 – – –
Steel with electro-deposited copper Solid Solid Solid Good in many environments Sulphur compounds –
Stainless steel Solid Solid Solid Good in many environments High chlorides content
Stranded Stranded Stranded – – –
Aluminum Solid Unsuitable Unsuitable Good in atmospheres containing low concentration of Sulphur and chloride Alkaline solutions Copper
Stranded – – – – –
Lead 5 Solid Solid Unsuitable Good in atmospheres with high concentration of sulphates Acid soils Copper
As coating As coating – – – Stainless steel

Material Dimensions

  • Several lightning protection system codes and standards define minimum dimensions for the components of a grounding system. These standards are designed to protect buildings and other inhabited or otherwise critical facilities.
  • Practical minimums are based on field experience and indicate what is needed to protect the installed equipment in a cost-effective way during the foreseeable technical lifetime, typically a few decades, taking into account local regulations. To ensure proper operation of the grounding system, periodic inspection and maintenance is needed

Minimum Dimensions of Earth Electrode as per IEC 623053 

  • Table 1 and Table 2 are based on standard IEC 62305-3 Ed 2. The tables list minimum dimensions for the lightning protection system equipment.
  • The following table lists the different materials and shapes that are used in air terminals, down conductors, and ground electrodes, including the cross-sectional area.

 Minimum Dimensions of Earth Electrodes

Table-7, IEC-62305-3
Material Configuration Dimensions
Earth Rod Diameter Earth Conductor Earth Plate
Copper, Tin-plated copper Stranded – 50 Sq.mm (8 mm) –
Solid round 15 mm 50 Sq.mm (8 mm) –
Solid tape – 50 Sq.mm (8 mm) –
Pipe 20 mm – –
Solid plate – – 500 × 500 mm
Lattice plate – – 600 × 600 mm
Hot-dipped galvanized steel Solid round 14 mm 78 Sq.mm (9.96 mm) –
Pipe 25 mm – –
Solid tape – 90 Sq.mm (10.7 mm) –
Solid plate – – 500 × 500 mm
Lattice plate – – 600 × 600 mm
Profile * – –
Bare steel (Shall be embedded in  concrete  for a minimum depth of 50 mm.) Stranded – 70 Sq.mm (9.4 mm) –
Solid round – 78 Sq.mm (9.96 mm) –
Solid tape 75 Sq.mm (9.72 mm)
Copper coated
steel		 Solid round 14 mm 50 Sq.mm (8 mm)
Solid tape 90 Sq.mm (10.7 mm)
Stainless steel Solid round 15 mm 78 Sq.mm (9.96 mm)
Solid tape 100 Sq.mm (11.28 mm)
Mechanical and electrical characteristics as well as corrosion resistance properties shall meet the requirements of the future IEC 62561 series.
In case of a type B arrangement foundation earthing system, the earth electrode shall be correctly connected at least every 5 m with the reinforcement steel.
* Different profiles are permitted with a cross-section of 290 mm2 and a minimum thickness of 3 mm, e.g. cross profile.

Minimum Cross-sectional Area of Air-termination Conductors

Minimum Cross-sectional Area of Air-termination Conductors

Table 6 (IEC 62305-3)
Material Configuration Cross-sectional Area Comments
Copper, tin-plated copper Solid tape 50 Sq.mm / 8mm * 2 mm min. thickness
Solid round1 50 Sq.mm / 8mm * 8 mm diameter
Stranded 1 50 Sq.mm / 8mm * 1.7 mm min. dia of each strand
Solid round*** 176 Sq.mm /15mm 16 mm diameter
Aluminum Solid tape 70  Sq.mm* 3 mm min. thickness
Solid round 50 Sq.mm / 8mm * 8 mm diameter
Stranded 50 Sq.mm / 8mm * 1.7 mm min. dia of each strand
Aluminum alloy Solid tape 50 Sq.mm / 8mm * 2.5 mm min. thickness
Solid round 50 Sq.mm / 8mm * 8 mm diameter
Stranded 50 Sq.mm / 8mm * 1.7 mm min. dia of each strand
Solid round*** 176 Sq.mm /15mm 16 mm diameter
Copper-coated aluminum alloy Solid round 50 Sq.mm / 8mm *
Hot-dipped galvanized steel ** Solid tape 50 Sq.mm / 8mm * 2.5 mm min. thickness
Solid round 50 Sq.mm / 8mm * 8 mm diameter
Stranded 50 Sq.mm / 8mm * 1.7 mm min. dia of each strand
Solid round*** 176 Sq.mm /15mm 16 mm diameter
Copper-coated steel Solid round 50 Sq.mm / 8mm *
Solid tape 50 Sq.mm / 8mm *
Stainless steel Solid tape 50 Sq.mm / 8mm * 2 mm min. thickness
Solid round*** 50 Sq.mm / 8mm * 8 mm diameter
Stranded 70 Sq.mm / 9.5mm* 1.7 mm min. dia of each strand
Solid round *** 176 Sq.mm /15mm* 16 mm diameter
* If thermal and mechanical considerations are important, these dimensions can be increased to 60 mm2 for solid tape and to 78 mm2 for solid round.
** The coating should be smooth, continuous and free from flux stains with a minimum thickness coating of 50 μm.
***Applicable for air-termination rods only. For applications where mechanical stress such as wind loading is not critical, a 10 mm diameter, 1 m long maximum air-termination rod with an additional fixing may be used.

Minimum values of the cross-section of the bonding conductors with different bonding bars

Minimum dimensions of conductors connecting internal metal installations to the bonding bar

Table-8 (IEC-62305-3)
Class of LPS Material Cross-section (mm2)
I to IV Copper 16 Sq.mm
Aluminum 25 Sq.mm
Steel 50 Sq.mm

 

Minimum dimensions of conductors connecting internal metal installations to the bonding bar

Table-9 (IEC-62305-3)
Class of LPS Material Cross-section (mm2)
I to IV Copper 6 Sq.mm
Aluminum 10 Sq.mm
Steel 16 Sq.mm

 

Table 10: Minimum thickness of metal sheets or metal pipes in air termination systems

(IEC/BS EN 62305-3 Table 3)
Class of LPS Material Thickness (1) t Thickness (2) t’
I to IV Lead – 2 MM
Steel (stainless, galvanized) 4 MM 0.5 MM
Titanium 4 MM 0.5 MM
Copper 5 mm 0.5 mm 5 MM 0.5 MM
Aluminum 7 mm 0.65 mm 7 MM 0.65 MM
Zinc – 0.7 mm – 0.70 MM
Thickness t prevents puncture, hot spot or ignition
Thickness t’ only for metal sheets if it is not important to prevent puncture, hot spot or ignition problems

Minimum Dimensions

Air Terminal Minimum Dimensions
Material Dimension
Copper, aluminum Tube with a 16 mm diameter, minimum wall thickness of 2 mm
8 mm (0.31 in) solid round
Steel 10 mm

 

Down Conductor Minimum Dimensions
Material Dimension
Copper 25 mm2 solid or stranded wire or solid tape
Aluminum 35 mm2 in solid or stranded aluminum
Steel 35 mm2  solid steel or stranded wires

 

Minimum Thickness of Tapes
Material Thickness
Copper 1 mm
Aluminum 2 mm
Galvanized steel 2 mm
Stainless steel 2 mm

 

Minimum Thickness of Strand Diameters in Stranded Cables
Material Thickness
Copper 1 mm
Aluminum 1.6 mm
Steel 1.6 mm

 

Ground Rod Minimum Dimensions

Material

Thickness
Copper Solid round 15 mm
Pipe 20 mm diameter with a minimum wall thickness of 2 mm
Copper clad solid steel 14 mm
Galvanized steel 16 mm
Galvanized steel, pipe 25 mm diameter with a minimum wall thickness of 2 mm

 

Horizontal Ground Electrode Minimum Dimensions

Material

Thickness
Copper 25 mm2 solid/strand/tape with a minimum 2 mm thickness
Galvanized steel, round wire 50 mm2 with a minimum 8 mm diameter
Galvanized steel, stranded 50 mm2 with a minimum strand diameter of 1.7 mm
Galvanized steel, tape 50 mm2 with a minimum thickness of 2 mm

 

Installation Depth of Ground Electrode

Ground Electrode Type

Installation Depth
Ground rod 3 meter
Horizontal ground electrode 0.6 meter

 

Typical Ground Electrode Length and Spacing

Minimum values

 Ground rod

Horizontal ground electrode
Length Typically, 3 Meter 10 Meter to 30 Meter as per soil type dependent
Loop diameter – 5 Meter to 6 Meter
Spacing Min. 2 × rod length –

Guideline for LPS System:

  • The following design guidelines need to be adhered to ensure safer installation of the external LPS.
  • Air Terminal:
  • Air terminal should be selected and provided only based on the protection angle or rolling sphere method
  • Proper safety distance between the air terminal and any metallic object needs to be maintained as per the calculation mentioned earlier to avoid dangerous spark-overs.
  • Different Material Jointing & Insulations:
  • Wherever incompatible materials to be joined (Ex. Copper with Aluminum), suitable bi-metal connectors should be used.
  • Suitable expansion joints must be provided on the horizontal conductors on top to take care of thermal effects.
  • Special conductor holders of insulating type need to be provided on top of the terrace floor for routing the conductor to ensure electrocution impact does not happen in case of water stagnation.
  • Equip potential Bonding:
  • Required measures to ensure shielding, bonding / equipotential bonding techniques are handled properly to avoid LEMPs.
  • Establishing connection for equipotential bonding with nearby metallic components need to be taken care of.
  • Joints should be mechanically and electrically effective, should be protected against corrosion or erosion from the elements or the environment and should present an adequate contact area.
  • Reinforcement Structure:
  • In the case of using reinforcement in concrete structures as lightning down conductor details should be decided at the design stage, before building construction begins.
  • Good contact between reinforcing bars to be ensured only by using connection clamps tested as per the requirement of IEC 62561-1
  • Down Conductor:
  • A down-conductor should be installed at each exposed corner of the structure where it is possible.
  • The Down conductor should run as straight and vertical as possible so that they provide the shortest and most direct path of a low impedance from the air termination to the earth electrode so that the lightning current can be safely conducted to earth.
  • The formation of loops in bring the down conductor shall be avoided, but where this is not possible the distance shall be maintained
  • There should be a test joint arrangement to have separation between down conductor and earth termination for safety and for measurement of earth resistance.
  • At least two down conductors are mandatory for any size of Building.
  • The termination of the down conductor to an earth electrode should be done minimum of 1 meter away from the structure and minimum of 0.5m depth inside the ground.
  • Earth electrodes for each down conductor shall be provided.
  • Connection of down conductors to gutters or down-spouts even if they are covered by insulating materials.
  • Usage of multiple connections with different materials should not be permitted.
  • Insufficient conductor dimensions (non-complying material as mentioned in IEC 62305-3 Table – 5) should be strictly avoided.
  • When the distance from down conductors to combustible materials cannot be assured, the cross section of the down conductor shall not be less than 100 mm²

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