Conventional Lightning Protection System Components – Part Four

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: Franklin Rod LPS, Franklin/Faraday Cage LPS. B- Non-Conventional lightning protection system, which includes: a- Active Attraction LPS, which includes: Improved single mast system (Blunt Ended Rods), Early streamer Emission System. b- Active Prevention/Elimination LPS, which includes: Charge Transfer System (CTS), 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.

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 theConnection Components which include but not limited to: Clamps, Connectors, Terminal components, Bridging components, Expansion pieces, Measuring points.

And I explained the Strike Termination Subsystem in this Article.

Also, in Article " Conventional Lightning Protection System Components – Part Two ", I began explaining the Conductor Subsystem through the following points:

• Function of Conductor Subsystems,
• Effects of Lightning Strikes on Conductor Subsystems,
• Conductor Subsystem Material Requirements.

And I explained in Article " Conventional Lightning Protection System Components – Part Three ", Types of Lightning Conductors which were:

Types of the Conductors in Conductor Subsystems The Conductor Subsystem is consisting of two types of conductors as follows: The Air-Termination Conductor (the Main Conductor), Down Conductor (The Extension Conductors).

Also, I explained the Installation Requirements for Down Conductors in this Article.

Today, I will explain How to use Natural Structure Components as down Conductors.

Conductor Subsystem -Continued

1- 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: The European Committee for Electrotechnical Standardisation (CENELEC). 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: Underwriters Laboratory (UL96 & 96A), The National Fire Protection Association (NFPA 780) The Lightning Protection Institute (LPI-175) Note: For heavy fault conditions, Conductor Size should be calculated in accordance with IEEE Std 80.

Natural Components Used as Down Conductors Natural conductive components can be used as an integral part of the lightning protection system. Natural components are typically metallic structural items that will not be modified during the life of the structure, such as reinforcing steel, metal framework and roofing/cladding. Natural components must meet minimum material requirements which listed in below Table#1 and be electrically continuous with secure interconnections between sections such as brazing, welding, clamping, seaming, screwing or bolts. Table#1 If the electrical continuity of the natural component cannot be guaranteed, then separate dedicated down-conductors should be used. When using natural components of the structure as a down-conductor system, the number of down conductors to be installed separately can be reduced or, in some cases, they can be dispensed with altogether. The following parts of a structure can be used as “natural components” of the down-conductor system: Metal Installations, Facade Elements, Mounting Channels and the Metal Substructures of Facades, Metal downpipes, Rebar in Reinforced Concrete, Rebar in Precast Concrete, Rebar in Prestressed Concrete.

1- Metal Installations Metal installations can be used as Down Conductors, provided that: The safe connection between the various parts is permanent and Their dimensions conform to the minimum requirements for down conductors. Notes: These metal installations may also be sheathed in insulating material. The use of conduits containing flammable or explosive materials as down conductors is not permitted if the seals in the flanges /couplings are non-metallic or the flanges/couplings of the connected pipes are not otherwise connected so as to be electrically conductive.

2- Facade Elements, Mounting Channels And The Metal Substructures Of Facades Facade elements, mounting channels and the metal substructures of facades (see fig.1)can be used as a natural down conductor system provided that: The dimensions meet the minimum requirements of down-conductor systems. For sheet metal, the thickness must not be less than 0.5 mm. Their electrical conductivity in vertical direction must be ensured. Fig.1: Facade Elements as Down Conductors Notes: If metal facades are used as a down-conductor system, they must be interconnected to ensure that the individual plates are safely interconnected with each other by means of screws, rivets, or bridging connections. There must be a safe connection capable of carrying currents to the air-termination system and also to the earth-termination system. If metal plates are not interconnected in accordance with the above requirement, but the substructure ensures that they are continuously conductive form the connection on the air termination system to the connection on the earth-termination system, then they can be used as a down-conductor system.

3- Metal Downpipes Metal downpipes can be used as natural down conductors, provided that: They are safely interconnected (brazed or riveted joints), They comply with the minimum wall thickness of the pipe of 0.5 mm. Fig.2: Metal Downpipes as Down Conductors Notes: If a downpipe is not safely interconnected, it can serve as a holder for the supplementary down conductor. This type of application is illustrated in Fig.2 The connection of the downpipe to the earth-termination system must be capable of carrying lightning currents since the conductor is held only along the pipe.

4- Use of Rebar in Reinforced Concrete Use of rebar for down-conductors is permitted provided that: The overall resistance from top to ground level is less than 0.2 ohms (On many occasions this is not practical to carry out. The standard then advocates that an external down conductor system be employed) A major part of vertical and horizontal connections are welded or securely connected, Construction is supervised ( this method is not recommended for existing buildings where the connections were not planned / documented and inspected prior to concrete pour. However, it can be used with existing buildings if the reinforcement is safely interconnected and Separate external down conductors must be installed). Note: If the metal frame of structures with a steel skeleton or the interconnected reinforced steel of the structure is used as a down-conductor system, then ring conductors are not required since additional ring conductors would not improve the splitting of the current. Methods for Connection to Concrete Reinforcing Steel A- Welding (see fig.3) Fig.3: Welding Method for Connection to Concrete Reinforcing Steel The internal interconnection of the rebar is recommended to be welded (where permitted) with a parallel overlap of 50 mm and weld length of not less than 30 mm. B- Mechanical Splices Mechanical splices also provide an acceptable electrical interconnection (see fig.4). Fig.4: Mechanical Splices Method for Connection to Concrete Reinforcing Steel C- Wire Ties Fig.5: Wire Ties Method for Connection to Concrete Reinforcing Steel While the interconnection by wire tie is permitted (where length of overlaps must be at least 20 times the diameter) (see fig.5), evidence shows that this is not suitable for a lightning-carrying connection, i.e. high current-carrying connections. The upper connection of the external LPS to the internal rebar carries the highest current density. It is important that this connection be secure, thus wire tie is not sufficient. D- Mechanical Clamps Fig.6: Mechanical Clamps Method for Connection to Concrete Reinforcing Steel Where mechanical clamps are used (see fig.6), they should be approved to EN 50164-1 and either two bonding conductors should be used, or one conductor with two clamps connecting to separate rebars. Notes: For the lower connection where tails are taken from rebar to the earth electrodes, the lower current density allows the use of a single welded connection or clamp. Compatibility between connected metals also needs to be considered. For ease of construction and installation, a grounding plate is recommended for connection of the LPS to the concrete member. If a grounding plate is not used, then attention should be given to corrosion protection at the air/concrete interface. If the rebar is brought out then 100 mm of silicon rubber or bitumen covering should be used. also, ground plates are convenient and eliminate the needs for corrosion protection (see fig.7). Interface corrosion protection is not required for copper, PVC covered copper or stainless steel conductors. Fig.7: Corrosion Protection Needs for Rebar Connections If welding is not permitted to the rebar, then an alternative is to use a dedicated lightning protection down-conductor that is embedded in the concrete. This conductor should be wire tied or clamped periodically to the rebar. For new build structures this can be decided at the early construction stage by using dedicated reinforcing bars or alternatively to run a dedicated copper conductor from the top of the structure to the foundation prior to the pouring of the concrete. This dedicated copper conductor should be bonded to the adjoining/adjacent reinforcing bars periodically. If there is doubt as to the route and continuity of the reinforcing bars within existing structures then an external down conductor system should be installed. General practice is to nominate specific rebars in the main structural columns as down conductors, and to ensure that these are continuous through the entire route to ground. The connection path should be vertical. Full interconnection should be made to horizontal elements such as floors and walls. For structures such as data processing centers this is more critical, and precast façade elements should also be bonded to provide effective electromagnetic shielding.

5- Use of Rebar in Precast Concrete Fig.8: Use of Rebar in Precast Concrete as Natural Down Conductor Precast concrete rebar is permitted to be used as above. However precast members such as floors do not normally have external access to rebar connections. For full interconnection, terminations should be provided for connection to columns and other members. Precast parts must have an electrically conductive connection between all terminal connections. The individual components must be interconnected on site during installation (see fig.8).

6- Use of Rebar in Prestressed Concrete Prestressed reinforced concrete is most commonly used for flooring, and rarely in vertical columns, hence it is not often used as a natural down-conductor. If it is to be used, care is recommended due to possible unacceptable mechanical consequences resulting from the lightning current or interconnection to the LPS. Only cables of 10 mm diameter or greater should be used, and several parallel cables should be used. Note that prestressed concrete is often used for facades, and in the construction process the stressing cables are often isolated from the other structural members. Should a side flash occur, there may be cracking of the facade with damage to the corrosion protection concrete grout used around the stressing cable. These cables are highly susceptible to corrosion. In such situations, both ends of the cables should be bonded to the LPS.

In the next Article, I will explain The Third Subsystem of the External Lightning Protection System; Grounding Electrode Subsystem. Please, keep following.

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