What is an Appliance Surge Protector?

Jeremy Laukkonen

An appliance surge protector is an apparatus that plugs into an electrical outlet and provides power to one or more devices. Rather than being a simple pass through, a surge protector has internal components that can protect an appliance from power spikes. Each surge protector contains one or more methods to suppress voltage spikes, though most units that are designed for appliances use metal oxide varistors (MOVs). In addition to protecting devices from outside surges, these units can buffer an electronic device from voltage spikes caused by the short, intense draws made by many large appliances.

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

Surge protectors can be used to safeguard everything from large home appliances to delicate electronics, such as computers and televisions. An appliance surge protector typically offers a number of outlets, which can allow several devices to be protected at once. A kitchen surge protector might have a fridge, blender, microwave, and other appliances connected. In another room, an appliance surge protector could provide power and protection to televisions, computers, phones, and other devices. Each surge protector typically operates with a single amp service, so large appliances may require separate units.

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

Most surge protectors use metal oxide varistors to protect the attached appliances. A metal oxide varistor operates by shorting out when presented with an excessively high voltage, which can protect the connected devices from a surge. Each surge tends to degrade the varistor, so an appliance surge protector that has been exposed to repeated voltage spikes will begin to lose its ability to function properly.

The primary purpose of an appliance surge protector is to safeguard electronics from outside power surges caused by events such as lightning strikes or issues with the power grid, though they can also be useful in protecting from spikes generated within the home. Many large appliances can generate intense loads when turned on or at other times during operation. When the compressor in a refrigerator or an air conditioner kicks on, it typically draws far more electricity than at other times. This can create a voltage spike that could adversely affect other appliances connected to the circuit. The metal oxide varistors inside an appliance surge protector can defeat these spikes and protect other devices on the circuit.

There are a variety of other surge suppression methods, though they are not commonly used in modern appliance surge protectors. Suppression diodes are commonly used in applications where many small surges occur, though they can typically handle only small current loads. Another variety of clamping semiconductors that operate similarly to MOVs are known as selenium voltage suppressors. These components can survive through more surge events than MOVs, though they are typically used in direct current (DC) applications.

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