Conventional Lightning Protection System Components – Part Two


In Article  "  Introduction to Lightning System Design- Part One ", I listed all terms, abbreviations and Symbols used in lightning field.

Also, in Article " Introduction to Lightning System Design- Part Two ", I answered the following questions:
  • What is Lightning? 
  • What are the types of Lightning flashes?
  • What is the shape of The Lightning Waveform?
  • How Lightning strikes can affect the electrical and/or electronic systems of a building?
  • What are the main effects of Lightning?

And in Article " Types Of Lightning Protection Systems LPS ", I list the main types of Lightning Protection Systems as follows:




Types of Lightning Protection Systems LPS







Types of Lightning Protection Systems LPS

Lightning protection systems for buildings and installations may be divided into three principal types as follows:

1- LPS for Protection for buildings and installations against direct strike by lightning, which includes:

A- Conventional lightning protection system, which includes:

  1. Franklin Rod LPS,
  2. Franklin/Faraday Cage LPS.


B- Non-Conventional lightning protection system, which includes:

a- Active Attraction LPS, which includes:

  1. Improved single mast system (Blunt Ended Rods),
  2. Early streamer Emission System.


b- Active Prevention/Elimination LPS, which includes:

  1. Charge Transfer System (CTS),
  2. Dissipation Array System (DAS).


2- LPS for Protection against overvoltage on incoming conductors and conductor systems,

3- LPS for Protection against the electromagnetic pulse of the lightning.



Notes on different Types of Lightning Protection Systems LPS

Each system’s design requires the following:

  1. The air terminal or strike termination device must be positioned so that it is the highest point on the structure.
  2. The lightning protection system must be solidly and permanently grounded. Poor or high resistance connections to ground are the leading cause of lightning system failure for each one of these systems.
  3. None of these systems claims to protect against 100% of the possibility of a lightning stroke arriving near protective area. A compromise must be made between protection and economics.



And in Article " Conventional Lightning Protection System Components – Part One ", I indicated the Conventional Lightning Protection System parts and components as follows:





Conventional Lightning Protection System LPS Components

The Conventional Lightning Protection System consists of two main parts:

1- The External Lightning Protection System, which includes:

  • Strike Termination Subsystem,
  • Conductor Subsystem,
  • Grounding Electrode Subsystem.


2- The Internal Lightning Protection System, which includes:

  • Equipotential Bonding Subsystem,
  • Surge Protection Subsystem.

Another important components of the Lightning Protection System is the Connection Components which include but not limited to:
  • Clamps,
  • Connectors,
  • Terminal components,
  • Bridging components,
  • Expansion pieces,
  • Measuring points.




Components of External Lightning Protection System

External Lightning protection systems have (3) distinct subsystems. They are:

1- Strike Termination Subsystem, which has (2) types:

  • Non-isolated system,
  • Isolated system.


And has also (4) forms as follows:

A- Vertical Air Terminals,

B- Horizontal air termination network, which include two sub-forms:

  1. Meshed conductor network,
  2. Overhead wires (Catenary wires).

C- Combination of Vertical Air Terminals and Horizontal air termination network,

D- Natural Air Terminals.

2- Conductor Subsystem,

3- Grounding Electrode Subsystem.

These individual Subsystems of an external LPS should be connected together using appropriate lightning protection components (LPC). This will ensure that in the event of a lightning current discharge to the structure, the correct design and choice of components will minimize any potential damage.






The Correct Choice Of Lightning Protection Components (LPC)


  • The correct choice of material, configuration and dimensions of the lightning protection components is essential when linking the various elements of an LPS together. 
  • The designer/user needs to know that the components, conductors, earth electrodes etc will meet the highest levels when it comes to durability, long term exposure to the environmental elements and perhaps most importantly of all, the ability to dissipate the lightning current safely and harmlessly to earth.
  • Various standards series have been compiled with this very much in mind. At present these standards are as follows:



Standards for Lightning Protection Systems


1- Within Europe:

Various standards series have been issued by (2) National Committees which are:

  1. The European Committee for Electrotechnical Standardisation (CENELEC).
  2. The International Electrotechnical Commission (IEC)


The CENELEC has released the EN 50164 series of standards. The EN 50164 series are component standards to which the manufacturers and suppliers of lightning protection components should test their products to verify design and quality. The EN 50164 series currently comprises of:

  • EN 50164-1 Lightning protection components (LPC) – Part 1: Requirements for connection components,
  • EN 50164-2 Lightning protection components (LPC) – Part 2: Requirements for conductors and earth electrodes,
  • EN 50164-3 Lightning protection components (LPC) – Part 3: Requirements for isolating spark gaps,
  • EN 50164-4: Lightning Protection Components (LPC) – Part 4: Requirements for conductor fasteners,
  • EN 50164-5: Lightning Protection Components (LPC) – Part 5: Requirements for earth electrode inspection housings and earth electrode seals,
  • EN 50164-6: Lightning Protection Components (LPC) – Part 6: Requirements for lightning strike counters,
  • EN 50164-7: Lightning Protection Components (LPC) – Part 7: Requirements for earthing enhancing compounds.


Notes:

  • The standards generally have an IEC prefix to their number (CEI for French versions). IEC standards are produced in English and French languages.
  • IEC and CENELEC generally work in parallel, and CENELEC members vote to adopt new IEC standards as CENELEC standards. The committees of CENELEC may choose to make some alterations to the IEC version.
  • Additionally, CENELEC produce their own standards to which IEC have no counterpart. CENELEC documents are produced in English, French and German and an approved CENELEC standard will have an EN prefix (or NE in the French language versions).


For example:

IEC 62305-1 (IEC version) is parallel to EN 62305-1 (CENELEC adopted copy of the above)
And both are parallel to BS EN 62305-1 (British National Standard adoption ofthe above)



2- Within USA:

Various standards series have been issued such as:

  1. Underwriters Laboratory (UL96 & 96A),
  2. The National Fire Protection Association (NFPA 780)
  3. The Lightning Protection Institute (LPI-175)


Note:

For heavy fault conditions, Conductor Size should be calculated in accordance with IEEE Std 80.





And I explained the Strike Termination Subsystem in this Article. Today, I will continue explaining the Conventional Lightning Protection System LPS Components.


Conductor Subsystem





1- Function of Conductor Subsystems

The function of conductor subsystems is to conduct the intercepted lightning current to the earth-termination system without intolerable temperature rises, for example, to damage the structure.





2- Effects of Lightning Strikes on Conductor Subsystems

As we indicated before in Article " Introduction to Lightning System Design- Part Two " that the waveform represents the lightning strike can be analyzed as follows:


 The lightning strike waveform

  • It is initially a pulse of very high currents up to hundreds of thousands of amperes in magnitude for durations of tens of microseconds, which require a conductor with big cross section. 
  • It then decays into a continuing current that more resembles direct current, lasting for up to a second.
  • Multiple pulses commonly occur during a single lightning event. The conductors in a lightning protection system must account for these effects brought on by the lightning waveform, which are:

  1. Electromagnetic forces and the development of high voltages due to the fast rise time of the pulse and the high peak current. Electromagnetic forces can damage or even break conductors.
  2. Side flash the resulting arc from side flash can ignite materials and can be catastrophic if a flammable atmosphere exists. This is very undesirable and is considered a failure of the lightning protection system.
  3. Heating and other ohmic effects on the conductor, so any point of high resistance can cause melting and failure. For example, a corroded or loose connection or a frayed conductor can cause a failure from ohmic heating.


In general, it is essential to minimize resistance and inductive reactance in the conductor subsystem of a lightning protection system.





3- Conductor Subsystem Material Requirements

  • All lightning protection materials should conform to EN 50164-1 and EN 50164-2 Lightning Protection Components requirements. The exceptions to these requirements are non-current carrying devices such as down-conductor fixings (clips), anti-vandal guards and mechanical supports.
  • The IEC and EN standards prescribe the minimum material requirements as summarized in the following Table:





Note:

The standards do not prescribe any relative performance advantages between these choices; all are adequate to conduct the lightning current. But, when considering service life, aesthetics, galvanic compatibility with building materials and ease of installation, there is generally a preferred clear choice of material for a given structure.





3.1 Comparison between Copper and Aluminum
as a Lightning Conductor Material

  • A conductor material should be chosen that is compatible with the surface it is to be located upon and that which it is to connect to. As a typical lightning protection system requires frequent bonds to nearby metallic items, compatibility with this should also be assessed.
  • Comparison between Copper and Aluminum Conductor Materials is indicated in the following table:


  
Aluminum
Copper
lower cost
More expensive than Aluminum
lighter weight
More heavy than Aluminum
Less compatible with many building materials
More compatible with many building materials
Cannot be buried in the ground
Can be buried in the ground
the aesthetics of eventual white corrosion of aluminum
the aesthetics of green verdigris of copper
Aluminum is prone to corrosion when in contact with limestone, plaster, mortar and cement. For this reason, aluminum conductors should not be placed in direct contact with such surfaces. Stand-off fixings can be used (see below figure), or PVC covered aluminum conductors used
care should be taken in areas with
sulphurous atmospheres (e.g. smoke stacks), where stainless steel or lead covered copper may be more appropriate


Aluminum is prone to corrosion in marine or sea-side environments


Aluminum should not be installed where it will be exposed to water run-off from copper (or copper alloy) surfaces
Copper should not be installed above galvanized, zinc or aluminum parts where water run-off occurs (unless parts are protected such as by PVC covering). Water run-off from the copper surface carries fine copper corrosion particles, which when deposited on lower galvanized, zinc or aluminum parts may results in severe corrosion.
Aluminum should not be installed on surfaces coated with alkaline based paint.

Aluminum should not be installed in locations subject to excessive moisture (i.e. in gutters, or on surfaces where water may be retained).



Therefore, most lightning protection systems are entirely copper or utilize an upper aluminum portion connecting to a copper earth termination system. As aluminum and copper are not compatible, a bimetallic joint should be used to interconnect these two materials.

Note:

As aluminum and copper are not compatible, a bimetallic joint should be used to interconnect these two materials.


Bimetallic Connector




3.2 Use of Dissimilar Metals in the Same Lightning Conductor Subsystem

  • Galvanic corrosion occurs when two dissimilar metals are in contact with each other in the presence of an electrolyte. In this situation, one metal becomes the anode and the other the cathode. The anode will tend to go into solution and therefore corrode. The electrolyte can be water with impurities from the air, other surfaces or from the metal itself
  • The following Table shows the potential difference between dissimilar metals. Combinations of metals with potential differences above 0.5 V should be rejected to avoid excessive corrosion.





For example:

A bare copper conductor should not be directly connected to steel, as the electrochemical potential difference is 0.53 V (≥ 0.5 V). However, if the copper is tin plated then the difference becomes that of tin (0.24 V), which is acceptable.

  • One method of reducing the effects of corrosion is to use plating of one or both of the metals to reduce the electrochemical potential difference. Commonly, tin plated copper conductors are used for this purpose. Tin plating also has the advantage of stopping the appearance of green verdigris coating and reducing the chance of theft (as the conductor no longer looks like copper). Tin plated copper should be used for connections to:

  1. Lead,
  2. Grey cast iron,
  3. Steel (stainless steel connections do not need to be tinned),
  4. Aluminum,
  5. Cadmium.


  • The following table shows the material of structure and its LPS compatible material:





3.3 Lightning Conductor Geometry

There are many choices of conductor geometry as follows:


   
  1. Tape,
  2. Solid Round,
  3. Stranded.


The following table indicates a comparison between above choices of conductor geometry as follows:






Note:

PVC covering limits the effectiveness when conductors are used as air terminations; it is common to see air-termination networks that are basically insulated. This does severely compromise the performance of the air-termination. The IEC standards do not specifically address PVC covered conductors. However, in the interest of improved performance, it is strongly recommend not using PVC covered conductors as air terminations.



In the next Article, I will explain the following points:
  • Types of Lightning Conductors,
  • Using Natural Structure Components As Down Conductors,
  • Installation Requirements For Down Conductors.
Please, keep following.



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