What is an Electrical Surge Protector?

Alan Rankin

An electrical surge protector is a device designed to protect electronic devices from potentially damaging increases in electric current. Lightning storms or irregularities in the power grid can sometimes cause electric current to jump to levels higher than normally required for household appliances. These brief surges, or spikes, can be dangerous to delicate computer components, which are found in many devices, not just computers. An electrical surge protector will divert, or ground, such spikes before they can reach the protected device.

Lightning is one potential cause of power surges.
Lightning is one potential cause of power surges.

Electricity generated by power plants is delivered to houses and buildings through high-voltage alternating current or direct current (AC or DC) power lines. This high-voltage transfer is more efficient for delivering power over long distances; transformers convert the power to the low voltages necessary for most household devices. A number of factors can cause this power to spike unexpectedly. The most common are lightning strikes to power lines, transformers, or elsewhere on the power grid. A single lightning strike can generate a trillion watts of power, causing a brief surge along the grid, triggering blackouts and equipment failure, as well as damaging unprotected electronics.

Lighting can strike power lines, transformers or elsewhere on the power grid.
Lighting can strike power lines, transformers or elsewhere on the power grid.

An electrical surge protector, also called a surge suppressor, is designed to prevent such spikes from reaching the protected equipment. While surge protectors are available for large-scale industrial and technological uses, the most common electrical surge protector is available for home use. It is a multi-outlet power strip popular for computer and home entertainment systems, although it can be used with any AC-powered device. Numerous versions are available, but the best have a higher joule rating, which is a measurement of the energy it can process without failing.

An electrical surge protector works by the inclusion of a device called a metal oxide varistor, or MOV. The MOV is a simple circuit that conducts electricity at safe levels of voltage. During a voltage spike, however, the MOV short-circuits, preventing the electricity from reaching the devices plugged into the surge protector. It diverts the excess electricity, allowing it to disperse harmlessly. The advantage of the MOV circuit is a fast response time, measured in nanoseconds, or billionths of a second.

Other circuits can achieve the same results as a MOV. These include gas-tube surge arrestors and avalanche diodes. Some do not react as quickly as the MOV, although they can handle even larger spikes in electricity. An advanced electrical surge protector will include several of these devices to provide multiple levels of protection. The proper electrical surge protector for a given situation depends on the value of the equipment or data being protected.

Varistors protect circuits against excessive voltage by acting as spark gaps.
Varistors protect circuits against excessive voltage by acting as spark gaps.

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