A surge protector, spike suppressor, surge suppressor, surge diverter, surge protection device (SPD), transient voltage suppressor (TVS), or transient voltage surge suppressor (TVSS) is an appliance or device intended to protect electrical devices in alternating current (AC) circuits from voltage spikes with very short duration measured in microseconds, which can arise from a variety of causes including lightning strikes in the vicinity. A surge protector limits the voltage supplied to the electrical devices to a certain threshold by short-circuiting current to ground or absorbing the spike when a transient occurs, thus avoiding damage to the devices connected to it. Key specifications that characterize this device are the clamping voltage, or the transient voltage at which the device starts functioning, the joule rating, a measure of how much energy can be absorbed per surge, and the response time.
Definitions 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.
Voltage spikes In an AC circuit, a voltage spike is a transient event, typically lasting 1 to 30 microseconds, that may reach over 1,000 volts. Lightning that hits a power line can cause a spike of thousands of volts. A motor, when switched off, can generate a spike of hundreds of volts. Spikes can degrade wiring insulation and destroy electronic devices like light bulbs, battery chargers, modems, televisions (TVs), and other consumer electronics. Spikes can also occur on telephone and data lines when AC main lines accidentally connect to them, or lightning hits them, or if the telephone and data lines travel near lines with a spike and the voltage is induced. A long-term overvoltage surge, lasting seconds, minutes, or hours, caused by power transformer failures such as a lost neutral or other power company error, is not protected by transient protectors. Long-term surges can destroy the protectors in an entire building or area. Even tens of milliseconds can be longer than a protector can handle. Long-term surges may or may not be handled by fuses and overvoltage relays.
Surge currents
A building's wiring adds electrical impedance that limits the surge current that reaches the loads when a voltage transient arrives at the service entrance (the point where the supply company's wiring enters a property). There is less surge current at longer wire distances and where more impedance is present between the service entrance and the load. Category A loads are more than 60 feet of wire length from the service entrance to the load. Category A loads can be exposed to 6 kV and 0.5 kA surge currents. Category B loads are between 30 and 60 feet of wire length from the service entrance to the load. Category B loads can be exposed to 6 kV and 3 kA. Category C loads are less than 30 feet from the service entrance to the load. Category C loads can be exposed to 20 kV and 10 kA. A coiled extension cord can be used to increase the wire length to more than 60 feet and increase the impedance between the service entrance and the load.
Protectors
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