The diverting and/or diminishing of excessive current and voltage from the AC power line, which can damage sensitive electronic equipment. Power surges generally last less than 50 microseconds, but can reach as much as 6,000 volts and draw 3,000 amps when they arrive at the equipment. There are two principal types of technologies used in surge protection devices. Shunt Mode - Divert The most common method is the use of a metal oxide varistor (MOV), which acts like a pressure relief valve to divert the surge to the neutral and/or ground lines. However, shunt mode methods can be problematic. Diverting high voltage to ground may damage equipment because all electronic devices are interconnected via ground. Since all data lines use ground as a signal reference, excessive voltage on that line can disrupt and impair networks and communications. In addition, MOVs can eventually stop working without warning. There are countless low-energy surges occurring all the time, even from innocuous, everyday operations such as turning a motor on and off. Each surge causes a minuscule degradation in the MOV. If the MOV is high quality, it can take decades before the countless surges render the MOV ineffective. In a poorly made device, they can add up to failure in a much shorter time. Series Mode - Block and Absorb Series mode surge protectors actually block high current and absorb excessive voltage. They do not divert current to ground, but limit the surge to acceptable levels that electronic equipment can handle. Another feature of series mode is the ability to suppress all excessive voltage rather than wait for a certain level. MOVs shunt the current when a preset voltage is reached, but series mode units can track the powerline voltage and activate the suppression components as soon as the voltage goes over the norm. Zero Surge, Inc., Frenchtown, NJ (www.zerosurge.com) is the pioneer in series mode technologies and began shipping their products in 1989. Hybrids Surge protectors may use both shunt mode and series mode methods in some combination. For example, they may use series mode for low-energy surges and shunt mode for high-energy surges. See voltage regulator, UPS, power surge, power swell, spike and sag.