It is far less expensive to protect against surges than to recover from them.
Q: Do computer manufacturers build transient voltage surge suppression (TVSS) and/or electronic filtering into their products?
A: There are two primary reasons why virtually no U.S. computer manufacturers include transient voltage surge suppression or suppression/filtering in their products: size and cost. With the advent of switch-mode power supplies and increasing market demand, computers and related peripheral equipment are likely to continue becoming smaller and less expensive. However, the quality of the power remains in the hands of the end-user. Almost all computer manufacturers make mention in their operation manuals of the need for quality electronic grade power to assure proper equipment operation.
Q: What surge current is associated with a lightning strike?
A: IEEE Std. 1100-1992 states that lightning generated currents range from a few hundred amperes to more than 500,000 amperes. The return strokes are typically less than the initial strokes, and as many as forty return strokes have been observed in some strikes.
Q: How long do lightning strikes last?
A: IEEE's Emerald Book reports that lightning impulses are relatively fast acting, existing for only 50-100 m sec. Rise time of the return stroke is typically a very short 0.1 - 10 m sec.
Q: How much energy is required to disrupt, destroy or otherwise endanger semiconductor devices?
A: The following table describes the thresholds of failure for selected semiconductors:
Device Type Disruption Destruction Energy
Digital integrated circuits 10-9 10-6
Analog integrated circuits 10-8 10-6
Low noise transistors and diodes 10-7 10-6
High speed transistors and integrated circuits 10-6 10-5
Low power transistors and signal diodes 10-5 10-4
Medium power transistors 10-4 10-3
Zeners and rectifiers 10-3 10-2
High power transistors 10-2 10-1
Power thyristors and power diodes 10-1 10-0
The Emerald Book notes that "Ösingle lightning or switching surge often causes physical damage that contributes to latent device failures. Exposure to lower magnitude surges cause either a gradual performance deterioration and/or intermittent operation. In such cases, it is often difficult to differentiate between software- and hardware-induced errors. Latent failures are observed primarily in semiconductor devices and insulating materials."
Q: Why is electrical transient and high frequency noise protection at service entrance a critical first step toward facility-wide protection?
A: More and more often, loads located at or near a building's service entrance are electronically driven. Variable speed drives, security and alarm systems, electronic trip circuit breakers and sophisticated electronic power monitoring systems are frequently found at service entrance. Safeguarding these devices from potentially catastrophic damage requires coordinated service entrance protection that includes both suppression and high frequency noise filtration.
In addition, electrical service entrances are exposed to the highest level of surge current generated by external events such as lightning and utility grid switching (refer to ANSI/IEEE C62.41 - 1991 for representative waveforms at service entrance).
Q: On what conductors does lightning actually enter a facility?
A: Most individuals are surprised to discover that lightning may enter a building coupled Line-to-Ground, Line-to-Neutral or Neutral-to-Ground. According to IEEE, the major mechanisms by which lightning produces surge voltages are:
A close-proximity lightning strike to objects on the ground or within cloud layers produces electromagnetic fields that can induce voltage on the primary and secondary circuit conductors (L-L, L-G).
Lightning ground-current flow resulting from nearby cloud-to-ground discharges couples onto the grounding network's common ground impedance paths, resulting in voltage differences across the network's length and breadth (L-G, N-G).
The rapid drop of voltage that may occur, when a primary gap-type arrester operates to limit the primary voltage, is coupled with transformer capacitance and produces surge voltages in addition to those coupled into the secondary circuit by normal transformer action (L-N).
A direct lightning strike injects high currents into the primary circuits, producing voltages by either flowing through ground resistance and causing a ground potential change or flowing through the surge impedance of the primary conductors. Some of this voltage couples from the primary to the secondary of the service transformers, by capacitance or transformer action or both, thus appearing in low-voltage AC power circuits (N-G, L-N).
Lightning directly strikes the secondary circuits. Very high currents and resulting voltages can be involved, exceeding the withstand capability of equipment and conventional surge protective devices rated for secondary circuit use (L-G, L-N).
Please review STATE OF THE ART TECHNOLOGY AND UL1449 2nd Edition.
This is probably the most important page to view to best understand the effectiveness of your TVSS.