A surge protector (or surge suppressor) is an appliance 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 by 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), or the obsolescent term 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 " protectors."