INTRODUCTION
Lightning is a capricious, random and unpredictable event. Its' physical characteristics include current levels sometimes in excess of 400 kA, temperatures to 50,000 degrees F., and speeds approaching one third the speed of light. Globally, some 2000 on-going thunderstorms cause about 100 lightning strikes to earth each second. USA insurance company information shows one homeowner's damage claim for every 57 lightning strikes. Data about commercial, government, and industrial lightning-caused losses is not available. Annually in the USA lightning causes more than 26,000 fires with damage to property (NLSI estimates) in excess of $5-6 billion.

The phenomenology of lightning strikes to earth, as presently understood, follows an approximate behavior:

1. The downward Leaders from a thundercloud pulse towards earth seeking out active electrical ground targets.

2. Ground-based objects (fences, trees, blades of grass, corners of buildings, people, lightning rods, etc., etc.) emit varying degrees of electric activity during this event. Upward Streamers are launched from some of these objects. A few tens of meters off the ground, a "collection zone" is established according to the intensified local electrical field.

3. Some Leader(s) likely will connect with some Streamer(s). Then, the "switch" is closed and the current flows. We see lightning.

Lightning effects can be direct and/or indirect. Direct effects are from resistive (ohmic) heating, arcing and burning. Indirect effects are more probable. They include capacitive, inductive and magnetic behavior. Lightning "prevention" or "protection" (in an absolute sense) is impossible. A diminution of its consequences, together with incremental safety improvements, can be obtained by the use of a holistic or systematic hazard mitigation approach, described below in generic terms.

LIGHTNING RODS
In Franklin's day, lightning rods conducted current away from buildings to earth. Lightning Rods, now known as Air Terminals, are believed to send Streamers upward at varying distances and times according to shape, height and other factors. Different designs of air terminals may be employed according to different protection requirements. For example, the utility industry prefers overhead shielding wires for electrical substations. In some cases, no use whatsoever of air terminals is appropriate (example: munitions bunkers). Air terminals do not provide for safety to modern electronics within structures.

Air terminal design may alter Streamer behavior. In equivalent e-fields, a blunt pointed rod is seen to behave differently than a sharp pointed rod. Faraday Cage and overhead shield designs produce yet other effects. Air terminal design and performance is a controversial and unresolved issue. Commercial claims of the "elimination" of lightning deserve a skeptical reception. Further research and testing is on-going in order to understand more fully the behavior of various air terminals.

DOWNCONDUCTORS, BONDING AND SHIELDING
Downconductors should be installed in a safe manner through a known route, outside of the structure. They should not be painted, since this will increase impedance. Gradual bends (min. eight inch radius) should be adopted to avoid flashover problems. Building steel may be used in place of downconductors where practical as a beneficial part of the earth electrode subsystem.

Bonding assures that all metal masses are at the same electrical potential. All metallic conductors entering structures (AC power, gas and water pipes, signal lines, HVAC ducting, conduits, railroad tracks, overhead bridge cranes, etc.) should be integrated electrically to the earth electrode subsystem. Connector bonding should be thermal, not mechanical. Mechanical bonds are subject to corrosion and physical damage. Frequent inspection and ohmic resistance measuring of compression and mechanical connectors is recommended.

Shielding is an additional line of defense against induced effects. It prevents the higher frequency electromagnetic noise from interfering with the desired signal. It is accomplished by isolation of the signal wires from the source of noise.

GROUNDING
The grounding system must address low earth impedance as well as low resistance. A spectral study of lightning's typical impulse reveals both a high and a low frequency content. The high frequency is associated with an extremely fast rising "front" on the order of 10 microseconds to peak current. 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 applies.

A single point grounding system is achieved when all equipment within the structure(s) are connected to a master bus bar which in turn is bonded to the external grounding system at one point only. Earth loops and differential rise times must be avoided. The grounding system should be designed to reduce ac impedance and dc resistance. The shape and dimension of the earth termination system is more important a specific value of the earth electrode. The use of counterpoise or "crow's foot" radial techniques can lower impedance as they allow lightning energy to diverge as each buried conductor shares voltage gradients. Ground rings around structures are useful. They should be connected to the facility ground. Exothermic (welded) connectors are recommended in all circumstances.

Cathodic reactance should be considered during the site analysis phase. Man-made earth additives and backfills are useful in difficult soils circumstances: they should be considered on a case-by-case basis where lowering grounding impedances are difficult an/or expensive by traditional means. Regular physical inspections and testing should be a part of an established preventive maintenance program.

TRANSIENTS AND SURGES
Ordinary fuses and circuit breakers are not capable of dealing with lightning-induced transients. Lightning protection equipment may shunt current, block energy from traveling down the wire, filter certain frequencies, clamp voltage levels, or perform a combination of these tasks. Voltage clamping devices capable of handling extremely high amperages of the surge, as well as reducing the extremely fast rising edge (dv/dt and di/dt) of the transient are recommended. Adopting a fortress defense against surges is prudent: protect the main panel (AC power) entry; protect all relevant secondary distribution panels; protect all valuable plug-in devices such as process control instrumentation, computers, printers, fire alarms, data recording & SCADA equipment, etc. Further, protect incoming and outgoing data and signal lines. Protect electric devices which serve the primary asset such as well heads, remote security alarms, CCTV cameras, high mast lighting, etc. HVAC vents which penetrate one structure from another should not be ignored as possible troublesome electrical pathways.

Surge suppressors should be installed with minimum lead lengths to their respective panels. Under fast rise time conditions, cable inductance becomes important and high transient voltages can be developed across long leads.

In all instances, use high quality, high speed, self-diagnosing protective components. Transient limiting devices may use a combination of arc gap diverters-metal oxide varistor-silicon avalanche diode technologies. Hybrid devices, using a combination of these technologies, are preferred. Know your clamping voltage requirements. Confirm that your vendor's products have been tested to rigid ANSI/IEEE/ISO9000 test standards. Avoid low-priced, bargain products which proliferate the market (caveat emptor).

DETECTION
Lightning detectors, available at differing costs and technologies, sometimes are useful to provide early warning. An interesting application is when they are used to disconnect from AC line power and to engage standby power, before the arrival of lightning. Users should beware of over-confidence in such equipment which is not perfect and does not always acquire all lightning data.

EDUCATION
Lightning safety should be practiced by all people during thunderstorms. Preparedness includes: get indoors or in a car; avoid water and all metal objects; get off the high ground; avoid solitary trees; stay off the telephone. If caught outdoors during nearby lightning, adopt the Lightning Safety Position (LSP). LSP means staying away from other people, taking off all metal objects, crouching with feet together, head bowed, and placing hands on ears to reduce acoustic shock.

Measuring lightning's distance is easy. Use the "Flash/Bang" (F/B) technique. For every count of five from the time of seeing the lightning stroke to hearing the associated thunder, lightning is one mile away. A F/B of 10 = 2 miles; a F/B of 20 = 4 miles, etc. Since the distance from Strike A to Strike B to Strike C can be as much as 5-8 miles. Be conservative and suspend activities when you first hear thunder, if possible. Do not resume outdoor activities until 20 minutes has past from the last observable thunder or lightning.

Organizations should adopt a Lightning Safety Policy and integrate it into their overall safety plan.

Guidelines for Providing Surge Protection
(Commercial, Institutional, Industrial Facilities)

INTRODUCTION
Damage from electrical transients, or surges, is one of the leading causes of electrical equipment failure. An electrical transient is a short duration, high-energy impulse that is imparted on the normal electrical power system whenever there is a sudden change in the electrical circuit. They can originate from a variety of sources, both internal and external to a facility.

NOT JUST LIGHTNING
The most obvious source is from lightning, but surges can also come from normal utility switching operations, or unintentional grounding of electrical conductors (such as when an overhead power line falls to the ground). Surges may even come from within a building or facility from such things as fax machines, copiers, air conditioners, elevators, motors/pumps, or arc welders, to name a few. In each case, the normal electric circuit is suddenly exposed to a large dose of energy that can adversely affect the equipment being supplied power.

The following is a guideline on how to protect electrical equipment from the devastating effects of high-energy surges. Surge protection that is properly sized and installed is highly successful in preventing equipment damage, especially for sensitive electronic equipment found in most equipment today.

GROUNDING IS FUNDAMENTAL
A surge protection device (SPD), also known as a transient voltage surge suppressor (TVSS), is designed to divert high-current surges to ground and bypass your equipment, thereby limiting the voltage that is impressed on the equipment. For this reason, it is critical that your facility have a good, low-resistance grounding system, with a single ground reference point to which the grounds of all building systems are connected. Without a proper grounding system, there is no way to protect against surges. Consult with a licensed electrician to ensure that your electrical distribution system is grounded in accordance with the National Electric Code (NFPA 70).

ZONES OF PROTECTION
The best means of protecting your electrical equipment from high-energy electrical surges is to install SPDs strategically throughout your facility. Considering that surges can originate from both internal and external sources, SPDs should be installed to provide maximum protection regardless of the source location. For this reason, a "Zone of Protection" approach is generally employed. The first level of defense is achieved by installing an SPD on the main service entrance equipment (i.e., where the utility power comes into the facility). This will provide protection against high energy surges coming in from the outside, such as lightning or utility transients.

However, the SPD installed at the service entrance will not protect against internally generated surges. In addition, not all of the energy from outside surges is dissipated to ground by the service entrance device. For this reason, SPDs should be installed on all distribution panels within a facility that supply power to critical equipment. Similarly, a third zone of protection would be achieved by installing SPDs locally for each piece of equipment being protected, such as computers or computer controlled devices. Each zone of protection adds to the overall protection of the facility as each helps to further reduce the voltage exposed to the protected equipment.

COORDINATION OF SPDS
The service entrance SPD provides the first line of defense against electrical transients for a facility by diverting high-energy, outside surges to ground. It also lowers the energy level of the surge entering the facility to a level that can be handled by downstream devices closer to the load. Therefore, proper coordination of SPDs is required to avoid damaging SPDs installed on distribution panels or locally at vulnerable equipment. If coordination is not achieved, excess energy from propagating surges can cause damage to Zone 2 and Zone 3 SPDs and destroy the equipment that you are trying to protect.

SPD RATINGS
When selecting an SPD for a given application, there are several considerations that must be made:

Application - Ensure that the SPD is designed for the zone of protection for which it will be used. For example, an SPD at the service entrance should be designed to handle the larger surges that result from lightning or utility switching.

System voltage and configuration - SPDs are designed for specific voltage levels and circuit configurations. For example, your service entrance equipment may be supplied three phase power at 480/277 V in a four-wire wye connection, but a local computer is installed to a single-phase, 120 V supply.

Let-through voltage - This is the voltage that the SPD will allow the protected equipment to be exposed to. However, the potential damage to equipment is dependent on how long the equipment is exposed to this let-through voltage in relation to the equipment design. In other words, equipment is generally designed to withstand a high voltage for a very short period of time, and lower voltage surges for a longer period of time. The Federal Information Processing Standards (FIPS) publication "Guideline on Electrical Power for Automatic Data Processing Installations" (FIPS Pub. DU294) provides details on the relationship between clamping voltage, system voltage, and surge duration.

As an example, a transient on a 480 V line that lasts for 20 microseconds can rise to almost 3400V without damaging equipment designed to this guideline. But a surge around 2300 V could be sustained for 100 microseconds without causing damage. Generally speaking, the lower the clamp voltage, the better the protection.

Surge current - SPDs are rated to safely divert a given amount of surge current without failing. This rating ranges from a few thousand amps up to 400 kiloamperes (kA) or more. However, the average current of a lightning strike is only approximately 20 kA., with the highest measured currents being just over 200 kA. Lightning that strikes a power line will travel in both directions, so only half the current travels toward your facility. Along the way, some of the current may dissipate to ground through utility equipment.

Therefore, the potential current at the service entrance from an average lightning strike is somewhere around 10 kA. In addition, certain areas of the country are more prone to lightning strikes than others. All of these factors must be considered when deciding what size SPD is appropriate for your application.

However, it is important to consider that an SPD rated at 20 kA may be sufficient to protect against the average lightning strike and most internally generated surges once, but an SPD that is rated 100 kA will be able to handle additional surges without having to replace the arrester or fuses.

Standards - All SPDs should be tested in accordance with ANSI/IEEE C62.41 and be listed to UL 1449 (2nd Edition) for safety.

Data Line Protection
Electrical transients are not confined to the electrical distribution system. They can enter a facility through phone/fax lines, cable or satellite systems, and local area networks (LAN). Therefore, in order to achieve maximum protection from surge damage, SPDs should be installed on all systems susceptible to electrical transients.

INSTALLATION
For maximum protection, SPDs should be installed as close to the equipment being protected as possible. Cable lengths should be as short and straight as possible to minimize the resistive path of the circuit to ground. A solid connection to the system grounding conductor is essential for proper operation of the SPDs. The surge protectors should be equipped with indicators that show if the circuit is grounded and operating properly, and the units installed so these indicators can be easily inspected.

All service entrance and distribution panel SPDs should only be installed by a licensed electrician familiar with the equipment and its use. In addition, Hartford Steam Boiler strongly recommends that a professional engineer experienced with surge suppression technology be retained to design the protection scheme for your facility to ensure all SPDs are properly sized and coordinated.

Call PDQIE to Craete a Plan for Personnel and Facility Protection (877) PDQ-4-FIX