6 Point Plan

TerraCon Industries principle supplier ERICO Lightning Technologies has developed a generic plan for the protection of structures and facilities. The concept behind the plan is that it prompts the user into considering a coordinated approach to lightning protection - one embracing all aspects of potential damage - from the more obvious direct strike to the more subtle mechanisms of differential earth potential rises and voltage induction at service entry points.

Lightning protection, grounding, equipotential bonding and surge protection are all interdependent disciplines. Reliable protection of structures, industrial and commercial operations and personnel, demands a systematic and comprehensive approach to minimizing threats caused by transients. No air terminal, for instance, can safely capture and arrest the lightning energy without a dependable route to ground. Equally, even the most expensive Transient Voltage Surge Suppressor (TVSS) devices are poor performers without a low impedance electrical ground. However, a low impedance ground can create problems if good installation bonding practices are not followed. These inter-dependent disciplines are best applied when looking at a total facility rather than an individual piece of equipment or portion of the facility.

ERICO has developed its comprehensive Six Point Plan to protect the overall structure, assure safety of its personnel and minimize exposure to transient damage based on cost-benefit and risk assessment principles. Implementation and coordination of all elements of the Plan are required for optimal protection and long term operational viability.

The six inter-dependent disciplines which form the protection plan are:

Point 1 - Capture the lightning discharge to a known and preferred attachment point

Capturing the lightning discharge to a known and controlled point involves the use of an effective air terminal(s) on the structure or facility to be protected.

In the design of area protection, it is important to realize that many points on the structure will be competing for the downward lightning leader by launching upward interception streamers.

Two fundamental concepts have emerged from recent research into the lightning attachment process and air terminal performance:

Air Terminals which produce copious amounts of corona (space charge) are likely to be less efficient in the interception of a lightning downward leader.
An optimum air terminal is one which launches an upward streamer when it is highly likely to convert into a stable, propagating leader (to intercept the downward leader)

Terracon Industries offers two alternatives to capturing the lightning discharge:

Eritech System 2000 Passive lightning protection system based on AS1768 Standard, utilising the conventional Franklin Rod approach to structural protection.
Eritech System 3000 Enhanced lightning protection system based on emerging air terminal technologies. This co-ordinated approach to structural protection utilises an enhanced air terminal and insulated down conductor cable. Protection design is based on the Collection Volume approach using our proprietory Benji CAD design software.

Point 2 - Convey the lightning energy safely to Ground

Conveying the large amount of energy content associated with a lightning discharge requires care in the layout and design of the down conductor system.

Conventional Lightning Down Conductors:

Conventional downconductors are un-insulated conductors, typically copper strip, or cable. To reduce the voltage rise, and the risk of sideflashing multiple downconductors are required. The use of multiple downconductors and associated grounding systems, can add substantially to the cost. The ascetics of multiple downconductors have historically been an issue with architects and building contractors. Some standards allow the use of the building reinforcing to be used as a downconductor if it has been tied together during construction. In the USA the cable should be smooth weave or rope lay construction. The Eritech System 2000 has a complete offering of such cables.

ERICORE Proprietary Down Conductor:

ERICO has developed its ERICORE dedicated insulated down conductor for use with its System 3000 Active Lightning Protection range. The cable is designed to provide a safe, insulated path, to ground for the captured lightning discharge. Only one downconductor is required which allows for a simple high efficiency grounding network to be constructed. ERICORE can be routed away from sensitive electronic equipment and requires a minimum of maintenance. It is ideal for where lightning protection is being retrofitted to existing buildings as it does not require the building reinforcing to be continuously electrically connected.

The cable is capable of withstanding the full energy of the lightning discharge and conveying this to the grounding system with minimal danger of side flashing to adjacent earth points. The ability of this unique down conductor to screen adjacent equipment from the large electro magnetic impulse associated with the discharge current, which may reach energy levels as high as 250kA 8/20µs, is also a measure of it's effectiveness in reducing damage by induction. This has particular applicability to Telecommunications towers where the downconductor is by necessity run parallel to the RF antenna cables down the length of the tower.

Key Benefits - ERICORE

Reduced risk of sideflashing - energy is constrained in the core of the cable
Lower impedance than conventional smooth weave or flat downcounductors - ensures reduced stress on cable, increasing reliability and allows for only one downconductor to be used.
Insulated cable - allows routing inside of building wiring risers
Lightning travels known path to ground - energy can be diverted away from the side of a facility where sensitive electronic equipment may be housed
No special bonding of structure required - minimises installation costs

Key Benefits - Conventional Downconductors

Exceeds requirements of Standards around the world.
Simple in concept

Point 3 - Dissipate the energy into a low impedanceGrounding System

The need to understand the characteristics of an earthing system under impulse conditions (associated with the higher Fourier spectral components of the lightning discharge) is crucial if an effective earth system is to be designed. An effect earth system is one in which the potential rise of the surrounding earth is minimized and the rate of potential fall off from the injection point is maximized.

Importance of ensuring a low impedance ground system

The importance of ensuring that the grounding system affords a low ground impedance and not simply a low resistance must be understood. A spectral study of the typical waveform associated with the lightning impulse reveals both a high frequency and low frequency component. The high frequency is associated with the extremely fast rising "front" (typically < 10 µs to peak current) of the lightning impulse while the lower frequency component resides in the long, high energy, "tail" or follow-on current in the impulse. The grounding system appears to the lightning impulse as a transmission line where wave propagation theory with the normal rules of reflection and group velocity apply.

Measurement of ground resistance with conventional low frequency instruments may not provide results which are indicative of the ground system's true effectiveness under lightning discharge conditions. ERICO has developed an ground System Analyzer in which a fast pulse is injected into the ground test point to simulate the performance under lightning impulse conditions. The peak current and voltage amplitude within an effective measurement interval of approximately 500ns is measured and used to calculate the effective impedance.

The magnitude of the current pulse is programmable according to the local conditions. The measurement window lies with current pulses of 1 to 5A, 10 to 250V (peak) and impedance range of 1.5 to 250 ohms. By effectively gating off any pulses returning to the instrument after about 500ns, the instrument can be used to 'isolate' distant grounds in a complex system (greater than 75m away), allowing only the ground-under-test to be measured without the need for disconnection.

The instrument is also capable of providing repetitive pulses at 30 second intervals to allow remote tracing of pulse currents, their magnitude and flow direction.

Point 4 - Eliminate differential ground voltages through Earth Potential Equalization

Ensuring that a single point earthing policy is adopted and that equi-potential earth bonding is used throughout the installation, will help eliminate common damage caused by differential earth potentials.

ERICO's Cadweld exothermic connections are generally used to achieve high quality eutectic molecular bonds.

The CADWELD connection

	A CADWELD welded connection produces a joint (or connection) superior in performance to any known mechanical or pressure type surface-to-surface contact connector. By virtue of its molecular bond, a CADWELD welded connection will not loosen or increase in resistance over the lifetime of the installation. Current carrying (fusing) capacity equal to that of the conductor Will not deteriorate with age Permanent molecular bond that cannot loosen or corode Will withstand repeated faults Low labor costs Made with inexpensive, lightweight and portable equipment No special skills are required No external power or heat required
	Cross section view of CADWELD TA connection showing the integrity of the electrical contact due to the molecular bond formed. Click on adjacent thumbnail to enlarge.
	CADWELD SS connection showing the integrity of the electrical contact due to the molecular bond formed. Click on adjacent thumbnail to enlarge.
	Cross section view of CADWELD SS connection showing the integrity of the electrical contact due to the molecular bond formed. Click on adjacent thumbnail to enlarge.
	Cross section view of CADWELD SS connection showing the integrity of the electrical contact due to the molecular bond formed. Click on adjacent thumbnail to enlarge.
	Cross section view of MECHANICAL compression connection showing poor integrity of electrical contact due to reduced surface contact and air voids. Click on adjacent thumbnail to enlarge.
	Cross section view of MECHANICAL compression connection showing poor integrity of electrical contact due to reduced surface contact and air voids. Click on adjacent thumbnail to enlarge.

Ideal for Grounding and Bonding Systems

Connections are often the weak point in ground circuits, especially if they are subjected to high currents and corrosion. The capacity of a grounding circuit to protect property and personnel depends on the quality of its connections. Only the CADWELD exothermic system can provide the permanent, low-resistance connection needed to create a long-lasting, reliable grounding network.

Key Benefits

Reduces step and touch potentials - safe for personnel
Reduces circulating currents due to differential ground voltages
Reduces the danger of side flashing

Point 5 - Protect AC power distribution circuits using suitable TVSS devices

It is not enough to simply provide Direct Strike area protection to a facility (points 1 through 4). Effective protection requires that the various service entry points also be protected with suitable surge arrestive devices. The mains point-of-entry supply to a facility is one such service which can create considerable damage to internal equipment if protection is not provided. The installation of voltage clamping devices capable of handling the large energy content (kA rating) of the over voltage surge, as well as reducing the extremely fast rising edge (dv/dt and di/dt) of this transient, are all important in the coordinated approach to overvoltage protection.

Key Benefits

Well designed TVSS devices help reduce the residual let-through voltage to downstream equipment
The use of Surge Reduction Filters in conjuction with TVSS clamping devices provide extremely low residual voltages as well as waveshape conditioning.
The Transient Discriminating range of surge protective devices have been designed to handle sustained overvoltage events without the need for fuses.

Point 6 -Protect low voltage data and control circuits using suitable TVSS devices

Protection of low voltage data or control line circuits such as telephone, modem, local area network and industrial SCADA wiring, requires that the surge protect device clamp the incident voltage to levels acceptable to the sensitive electronic interface circuits. Such protection generally requires that a multi-stage protective hybrid circuit be employed where both speed of activation and energy handling capacity are optimized.

Key Benefits

Transient barriers utilise various circuit and component topographies to maximize the protection level
Wide range of operating frequencies and clamping voltage levels are available to meet a variety of signalling protocols