Surge suppressors are used to protect equipment from transient over voltages in power, data, and telephone circuits. Surge protection devices carry specifications for maximum surge current, clamping voltage, number of protected lines, and operating temperature. Maximum surge current is the maximum, allowable current for a single impulse waveform with a continuous voltage applied. Higher-level surge current capacities are required for high-exposure applications where very large transients are present. Clamping voltage is the voltage at which surge suppressors conduct their fully-rated current. The number of protected lines is the number of "pairs" or lines protected from power surges. Operating temperature is another important parameter to consider when selecting surge suppressors.
There are many different types of surge suppressors. Transient voltage surge suppressors (TVSS) protect against a temporary excess voltage and/or current. Data line and DC signal surge suppressors are designed to protect equipment from transient over voltages present on data or DC signal lines. Single-phase surge suppressors protect against transient over voltages present on single-phase AC power lines. Similarly, three-phase surge suppressors protect against transient over voltages on three-phase AC power lines. Plug-in style surge suppressors are designed to plug into wall outlets. Lightning arrestors are designed to protect equipment from power surges produced by lightning. Coaxial surge suppressors have a coaxial connector form factor and are used with RF equipment.
Selecting surge suppressors requires an understanding of surge protector technologies. Choices include metal oxide varistors (MOVs) and gas tubes. MOVs have high-energy capabilities, good reliability, and consistent performance. They also have a non-linear clamping curve and fatigue rapidly at higher amperage levels. Gas tubes have higher energy capabilities than MOVs. They typically consist of two electrodes held at a close distance so that high voltages between the electrodes simply arc through the air to effectively clamp the voltage. Gas tubes are very slow, but can handle very large surges.
Surge suppressors may use silicon avalanche diodes, silicon thyristor diodes, or hybrid technologies instead of MOVs or gas tubes. Silicon avalanche diodes have high clamping voltages, but a limited power-handling capacity that is destroyed easily by the power levels encountered in typical power-line surges. Silicon avalanche diodes are used most often in data-line protectors and on circuit boards as static protectors. Silicon thyristor diodes are used mainly to protect telecom systems. Hybrids attempt to incorporate all the major advantages of the different types of surge suppressors and surge protection technologies.
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