Conventional Lightning Protection System Components – Part Six



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

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.





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.





And I explained the Strike Termination Subsystem in this Article.

Also, I explained the Conductor Subsystem in the following Articles:


And in Article " Conventional Lightning Protection System Components – Part Five ", I explained the Grounding Electrode Subsystem.


For more information, you can review the following Articles:



Today, I will explain the second part of Lightning Protection System; The Internal Lightning Protection System.


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.







1- The Internal Lightning Protection System





1.1 The Internal Lightning Protection System


External and Internal Lightning Protection Systems


When current from the lightning pulse flows through a conductor which have impedance consisting of resistive and inductive components, there is voltage drop from this impedance. If this voltage becomes high enough, it can exceed the dielectric breakdown value of the medium surrounding the conductor. When that occurs, an arc (commonly termed as sideflash) is formed. It is desirable to prevent arcing and sideflash in lightning protection systems because the medium through which the arc occurs, lie wood, for example, could be ignited.






1.2 Function of Internal Lightning Protection System

The function of the internal lightning protection is to prevent hazardous sparking inside the building or structure. This could be due, following a lightning discharge, to lightning current flowing in the external LPS or indeed other conductive parts of the structure and attempting to flash or spark over to internal metallic installations.





1.3 How Internal Lightning Protection System prevent hazardous sparking inside the building or structure?

Mainly, this is achieved by (2) means as follows:

  1. Equipotential bonding, or,
  2. Ensuring a safety (insulation) distance between the components of the lightning protection system and other conductive elements inside the building or structure.





1.4 Components Of The Internal Lightning Protection System

The Internal Lightning Protection System includes (2) subsystems as follows:

  1. Equipotential Bonding Subsystem,
  2. Surge Protection Subsystem.






2-  Equipotential Bonding Subsystem




2.1 Equipotential Bonding Subsystem

Equipotential bonding is simply the electrical interconnection of all appropriate metallic installations/parts, such that in the event of lightning currents flowing, no metallic part is at a different voltage potential with respect to another because if the metallic parts are essentially at the same potential then the risk of sparking or flash over is nullified.

This electrical interconnection can be achieved by:

  1. Using natural/fortuitous bonding or
  2. Using direct connection by specific bonding conductors that are sized according to BS EN 62305-3,
  3. Using non-direct connection, where the direct connection with bonding conductors is not suitable, by using surge protection devices (SPDs) which must conform to BS EN 62305-4.


General Notes For Equipotential Bonding:

  • In small buildings, bonding bar should be located close to the main distribution board (MDB) and also closely connected to the earth termination system with short length conductors.
  • In large facilities, several interconnected bonding bars may be needed. Interconnection should be via a dedicated internal ring (or partial ring), or via the internal reinforcing of the concrete construction
  • An isolated LPS only requires bonding to the structure at ground level.
  • Non-isolated LPS’s require bonding to the structure at ground level, and at locations where separation distance requirements cannot be maintained.
  • For structures taller than 30m the standard recommends that equipotential bonding is carried out at basement/ground level and every 20 m above that.





2.2 Parts Of Equipotential Bonding Subsystem

According to IEC 60364-4-41, equipotential bonding subsystem consists of:

  1. Main equipotential bonding,
  2. Supplementary equipotential bonding.





2.2.1 Main Equipotential Bonding

Every building must be given a main equipotential bonding, the following building systems and conductive materials have to be directly integrated into this main equipotential bonding:

  • Telecom networks,
  • Data system,
  • Power utility cables,
  • Internal gas pipe,
  • Metal water supply pipe,
  • Metal drain pipe,
  • Central heating system,
  • Foundation earth electrodes or lightning protection earth electrodes,
  • Earthing conductor for antennas, if any,
  • Earthing conductor for telecommunication systems, if any,
  • Protective conductors of the electrical installation in accordance with IEC 60364 series (PEN conductor for TN systems and PE conductors for TT systems or IT systems),
  • Main equipotential bonding conductor,
  • Metal shields of electrical and electronic conductors,
  • Metal cable sheaths of high-voltage current cables up to 1000 V,
  • Conductive parts of the building structure (e.g. lift rails, steel skeleton, ventilation and air conditioning ducting).


The following installation components have to be integrated indirectly into the main equipotential bonding via isolating spark gaps:

  • installations with cathodic corrosion protection


Note:

Permission should be obtained from the operator of these systems to ensure there are no conflicting requirements.

Below figure (based on BS EN 62305-3 fig E.45) gives example for these bonding connections:



Main Equipotential Bonding

 from above Figure, we can note the following:

  • The power cable is bonded via a suitable SPD, downsream from the electric meter, to the equipotential bonding bar.
  • The screen of any antenna cable along with any shielded power supply to electronic appliances being routed into the structure should also be bonded at the equipotential bar.
  • If gas or water pipes entering the structure have insulated inserts incorporated into them, then these insulated sections should be bridged by suitably designed SPDs. Agreement with the relevant utility should be sought prior to installation.






2.2.2 Supplementary equipotential bonding

  • If the disconnection conditions, from supply, of the respective system configuration cannot be met for an installation or a part of it, a supplementary local equipotential bonding is required.
  • The supplementary equipotential bonding must be used for installations or parts of installations of IT systems with insulation monitoring.
  • The supplementary equipotential bonding is also required if the environmental conditions in special installations or parts of installations mean a particular risk.
  • The IEC 60364 series Part 7 draws attention to the supplementary equipotential bonding for operational facilities, rooms and installations of a particular type. These are, for example:

  1. IEC 60364-7-701 Rooms with bathtub or shower,
  2. IEC 60364-7-702 Swimming pools and other basins,
  3. IEC 60364-7-705 for agricultural and horticultural premises.





2.2.3 The Difference Between Main And Supplementary Equipotential Bonding

  • The conductors of supplementary equipotential bonding can be chosen to be smaller than that of the main equipotential bonding,
  • Supplementary equipotential bonding can be limited to a particular location.





3-  Considerations For Different Cases Of Main Equipotential Bonding In Any Installation




3.1 Lightning Equipotential Bonding For External LPS
And External Conductive Parts


In the case of equipotential bonding for an external LPS and external conductive parts, the following considerations must be noted:

  • It should be carried out in the basement or at ground level of the structure.
  • The bonding conductor should have a direct connection to an earth bonding bar which in turn should be connected to the earth termination system.
  • It should be carried out as near to the point of entry into the structure as possible.
  • If direct bonding is not acceptable then suitably designed SPDs should be used.





3.2 Lightning Equipotential Bonding Of External Services

External Services entering the facility may include:

  1. Telephone and telecommunication lines,
  2. Cable TV circuits,
  3. Antenna feeders,
  4. Power lines,
  5. Pipe work (water, air, gas, etc),
  6. Metal ducts,


In the case of equipotential bonding for External Services, the following considerations must be noted:

  • The bonding bar should be located as close as possible to, and connect to, all external metallic services entering the facility (gas pipes, water, power, telephone, etc).
  • Where permitted, these items should be bonded directly to the bonding bar. In the cases of electrical, electronic and tele/data communications services, bonding should be via surge protective devices.
  • It is good practice to bring all services into the structure in close proximity to each other (i.e. enter the structure near ground level at one common location) to make Equipotential bonding as close as possible to the entry point which simplify the bonding requirements, and minimize voltage differentials between each service.
  • If the metallic and electrical services enter the structure at different locations and thus several bonding bars are required, these bonding bars should be connected directly to the earth termination system, which preferably should be a ring (Type B) earth electrode arrangement. If a Type A earth electrode arrangement is used then the bonding bars should be connected to an individual earth electrode (rod) and additionally interconnected by an internal ring conductor.
  • If the services enter the structure above ground level, the bonding bars should be connected to a horizontal ring conductor either inside or outside the outer wall and in turn be bonded to the external down conductors and reinforcing bars of the structure.
  • If the cables (power, telecom etc) entering the structure are of a shielded construction, then these shields should be connected directly to the equipotential bonding bar. The other ‘live’ cores should be bonded via suitable SPDs.
  • Where structures are typically computer centers or communication buildings where a low induced electromagnetic field is essential, then the ring conductors should be bonded to the reinforcing bars approximately every 5 metres.





3.3 Lightning Equipotential Bonding For Internal Systems

Internal metallic items in the facility may include:

  1. Water pipes,
  2. Gas pipes,
  3. Heating pipes,
  4. Air ducts,
  5. Lift shafts,
  6. Electrical services,
  7. Hand rails.


In the case of equipotential bonding for Internal metallic items, the following considerations must be noted:

  • Bonding at ground or basement level should be made to the above internal metallic items.
  • If the conductors within the structure have an outer screening or are installed within metal conduits then it may be sufficient to only bond these screens and conduits.
  • However, this may not avoid failure of equipment due to overvoltages. In this case coordinated SPDs designed and installed in accordance with BS EN 62305-4 should be used.
  • If these internal conductors are neither screened nor located in metal conduits, they should be bonded using suitably designed SPDs.
  • These items should comply with the separation distance requirements, as bonding and connection to the LPS at other locations may be required.


Note:

For buildings higher than 30 m, it is recommended that equipotential bonding requirements are repeated at a level of 20 m and every 20 m above that.





3.4 Lightning Equipotential Bonding Of Roof Top Fixtures

  • Special problems may occur when roof-mounted fixture/structures (such as vents, skylights, air-handling units, pipes, etc), which are often installed at a later date, protrude from zones of protection.
  • If, in addition, these roof-mounted structures contain electrical or electronic equipment, such as roof-mounted fans, antennas, measuring systems or TV cameras, additional protective measures are required.


Equipotential bonding of roof top fixtures ,generally, governed by (3) scenarios as follows :


Scenario#1

If the roof mounted equipment is not protected by the air termination system but can withstand a direct lightning strike without being punctured

In this case, Equipotential bonding of roof top fixtures requirements will be as follows:

  • The casing of the equipment should be bonded directly to the LPS.
  • If the equipment has metallic services entering the structure (gas, water etc) that can be bonded directly, then these should be bonded to the nearest equipotential bonding bar.
  • If the service cannot be bonded directly (power, telecom, cables) then the ‘live’ cores should be bonded to the nearest equipotential bonding bar, via suitable Type I lightning current SPDs.



Scenario#2

If the roof mounted equipment cannot withstand a direct lightning strike and there is sufficient space on the roof for achieving a separation distance

In this case, Equipotential bonding of roof top fixtures requirements will be as follows:

  • An air rod or suspended conductor should be installed as in below Figure. This should offer sufficient protection and is so spaced from the equipment, such that it complies with the separation distance. This air rod/suspended conductor should form part of the air termination system.


Air Rod or Suspended Conductor for Roof Mounted Equipment

  • If the equipment has metallic services entering the structure (gas, water etc) that can be bonded directly, then these should be bonded to the nearest equipotential bonding bar.
  • If the other electrical services do not have an effective outer core screen, then consideration should be given to bonding to the nearest equipotential bonding bar, via Type II overvoltage SPDs.
  • If the electrical services are effectively screened but are supplying electronic equipment, then again due consideration should be given to bonding, via Type II overvoltage SPDs.
  • If the electrical services are effectively screened but are not supplying electronic equipment, then no additional measures are required.


Scenario#3

If the roof mounted equipment cannot withstand a direct lightning strike and there isn’t sufficient space on the roof for achieving a separation distance

In this case, Equipotential bonding of roof top fixtures requirements will be as follows:

  • An air rod or suspended conductor should be installed and there should be a direct bond to the casing of the equipment, the air rod/suspended conductor should be connected into the air termination system.
  • If the equipment has metallic services entering the structure (gas, water etc) that can be bonded directly, then these should be bonded to the nearest equipotential bonding bar.
  • If the service cannot be bonded directly, (power, telecom, cables) then the ‘live’ cores should be bonded to the nearest equipotential bonding bar, via suitable Type I lightning current SPDs.


These scenarios are summarized in the below flow chart:


Flow Chart for Protecting Roof Mounted Equipment


However, to eliminate the need to bond, it may be possible to select air-termination location and height so the fixture is protected by the air-termination, but positioned far enough distance away so that bonding is not required (see below figure).



Requirements of  Protected Roof Mounted Equipment for bonding



In the next Article, I will explain the following points:

  • Components of Equipotential Bonding Subsystem,
  • Separation distance requirements,
  • Test and Inspection of the Equipotential Bonding Subsystem,
  • General Overview of Surge Protection Subsystem.

Please, keep following.






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