Surge protection

A surge protector (or surge suppressor or surge diverter) is an appliance or device designed to protect electrical devices from voltage spikes. A surge protector attempts to limit the voltage supplied to an electric device by either blocking or shorting to ground any unwanted voltages above a safe threshold. This article primarily discusses specifications and components relevant to the type of protector that diverts (shorts) a voltage spike to ground; however, there is some coverage of other methods.

The terms surge protection device (SPD) and transient voltage surge suppressor (TVSS) are used to describe electrical devices typically installed in power distribution panels, process control systems, communications systems, and other heavy-duty industrial systems, for the purpose of protecting against electrical surges and spikes, including those caused by lightning. Scaled-down versions of these devices are sometimes installed in residential service entrance electrical panels, to protect equipment in a household from similar hazards.

Many power strips have basic surge protection built in; these are typically clearly labeled as such. However, power strips that do not provide surge protection are sometimes erroneously referred to as "surge protectors".

These are some of the most prominently featured specifications which define a surge protector for AC mains, as well as for some data communications protection applications.

Also known as the let-through voltage, this specifies what spike voltage will cause the protective components inside a surge protector to divert unwanted energy from the protected line. A lower clamping voltage indicates better protection, but can sometimes result in a shorter life expectancy for the overall protective system. The lowest three levels of protection defined in the UL rating are 330 V, 400 V and 500 V. The standard let-through voltage for 120 V AC devices is 330 volts.

Underwriters Laboratories (UL), a global independent safety science company, defines how a protector may be used safely. UL 1449 became compliance mandatory with the 3rd edition in September 2009 to increase safety compared to products conforming to the 2nd edition. A measured limiting voltage test, using six times higher current (and energy), defines a voltage protection rating (VPR). For a specific protector, this voltage may be higher compared to a Suppressed Voltage Ratings (SVR) in previous editions that measured let-through voltage with less current. Due to non-linear characteristics of protectors, let-through voltages defined by 2nd edition and 3rd edition testing are not comparable.

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