Surge Protective Device
Frequently Asked Questions
1. What are surges (also called transients, impulses, spikes)?
An electrical surge (transient voltage) is a random, highenergy, short duration electrical disturbance. As shown in Figure 1, it has a very fast rise time (1–10 microseconds). Surges, by definition, are subcycle events and should not be confused with longer duration events such as swells or temporary overvoltages. High-energy surges can disrupt, damage or destroy sensitive microprocessor-based equipment. Microprocessor failure results from a breakdown in the insulation or dielectric capability of the electronics.
Approximately 80% of recorded surges are due to internal switching transients caused by turning on/off motors, transformers, photocopiers or other loads. The IEEE C62.41 surge standard has created the Category B3 ringwave and the B3/C1 combination wave to represent higher energy internal surges.
Externally generated surges due to induced lightning, grid switching or from adjacent buildings account for the remaining recorded surges. The Category C3 combination wave (20 kV, 10 kA) represents high-energy surges due to lightning.
2. Why is there a need for surge protective devices?
In the coming years, electronic devices will represent half ofour electrical demand. Electronics consist of microprocessors that rely on digital signals: fast on/ off coded sequences. Distortion on the power or signal lines may disrupt the sensitive signal sequence. As electronic components become smaller and more powerful, they become more sensitive. The tremendous proliferation in the use of sensitive electronic equipment—sensitive by virtue of circuit density (microchips having literally thousands of transistors on a single chip)—is now incorporated into almost every new electrical device.
Surge protection is now the standard technology for increasing the reliability and uptime of microprocessors. Microprocessors can be “upset,” “degraded” or “damaged” by surge events. Depending on the magnitude of the surge, the system configuration and the sensitivity of the load. Table above summarizes the results of a major survey conducted by Dranetz on the effects of surges on different microprocessor equipment.