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See surge suppression.

surge suppression

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 ( is the pioneer in series mode technologies and began shipping their products in 1989.

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.

Shunt Mode and Series Mode
This American Power surge protector is a hybrid. The capacitors absorb low-energy surges, while the MOVs divert the high energy. (Image courtesy of American Power Conversion Corporation.)

All Series Mode
This diagram shows how Zero Surge protectors ( operate. The current is not diverted to ground. The Zero Surge units use coils and capacitors to block and absorb the energy and release only acceptable levels to the equipment. There are no parts that degrade with each surge encountered.

Keep Running Smoothly
An excellent safeguard is to power a computer from an uninterruptible power supply (bottom) that plugs into a series mode suppressor (top), which plugs into the wall. The high energy of a surge is brought down to low levels before it reaches the UPS. The Zero Surge suppressor and American Power UPS are high quality units.

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