There’s no shortage of options when it comes to surge protection. It may be difficult to tell the difference among products and systems, and what type of surge protection device (SPD) is right for the application. Here are a few and notes to help sort what’s out there.
1. Technology Matters
Manufacturers utilize several different technologies in surge protection. Silicon avalanche suppressor diode (SASD) designs generally provide more reliable, long-lasting protection. Differentiating between Type 1, Type 2 and Type 3 SPDs is also significant, as described below.
2. MOV
Metal oxide varsitor (MOV) SPDs are non-linear variable resistors with semiconductor properties that were originally designed to protect electrical motor windings against wiring insulation breakdowns. There are two advantages associated with MOVs in regard to surge suppressors: They are inexpensive and they divert reasonably high values of transient current.
However, there are several downsides to MOV technology. Primarily, this type of SPD degrades significantly with use. Also, an MOV-based suppressor device cannot maintain a stable VPL as it conducts increasing current values, leading to potential equipment damage. Finally, varistors create “thermal runaway” conditions when their initial clamp points or VPLs are set too close to the nominal AC line voltage.
3. SASD
Compared to other suppression technologies, the advantages associated with the use of SASDs are numerous. Like the components within the sophisticated circuitry of modern electronic equipment that they are intended to protect, SASDs are true solid state semiconductors. Unlike MOVs, SASD-based surge suppression components do not degrade or cause thermal runaway conditions. As long as their energy dissipating capabilities are not exceeded, they will function perpetually.
Also, SASDs turn on faster than MOVs and respond more rapidly to transient overvoltages. A SASD-based transient suppressor can be reasonably expected to function with an in-circuit response time of five nanoseconds or less. Finally, quality SASD-based suppressor products maintain a stable VPL at any location upon the AC power system while conducting maximum current values.
4. Specifics are Key
Generally, the difference between Type 1, 2 and 3 SPDs revolves around the current rating of each. Type 1 SPDs have a higher rating and are typically used in service-sector and industrial buildings, and are engineered to protect against direct lightning strikes. Type 2 SPDs are the primary protection system for low-voltage installations. Type 3 SPDs have a low discharge capacity and are generally used as a supplementary solution for Type 2 applications.
In addition to the type of SPD, it is critical to address specific voltage requirements in the application for the best fit. Furthermore, ensuring the SPD meets all critical standards for performance, reliability and safety is elemental.
5. Filters Are Not Enough
A filter’s operational characteristics, by definition, are frequency dependent. It cannot adequately protect critical electronic loads from lightning-induced transient surges, nor can the filter protect against transients generated from non-lightning sources. It is designed to attenuate noise occurring within a band of repeating frequency ranges at relatively low voltage and current amplitudes.
Filtering technology (as well as built-in surge protection) typically is a good fit as a supplement to a high-quality SPD.
