A surge protector
(or spike suppressor
, or surge suppressor
, surge diverter
) is an appliance or device intended to protect electrical devices
from voltage spikes
in alternating current
(AC) circuits. 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 give a spike of over 100,000 volts and can burn through wiring insulation and cause fires, but even modest spikes can destroy a wide variety of electronic devices, computers, battery chargers, modems and TVs etc, that happen to be plugged in at the time. Typically the surge device will trigger at a set voltage, around 3 to 4 times the mains voltage, and divert the current to earth. Some devices may absorb the spike and release it as heat. They are generally rated according to the amount of energy in joules they can absorb.
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 give many thousands, sometimes 100,000 or more volts. A motor when switched off can generate a spike of 1,000 or more volts. Spikes can degrade wiring insulation and destroy electronic devices like light bulbs
, battery chargers, modems and TVs etc.
Spikes can also occur on telephone and data lines when AC main lines accidentally connect to them or lightning hits them or the telephone and data lines travel near lines with a spike and the voltage is induced.
A long term surge, lasting seconds, minutes, or hours, caused by power transformer failures such as a lost neutral or other power company error, are 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.
A transient surge protector attempts to limit the supplied to an electric device by either blocking or current to reduce the voltage below a safe threshold. Blocking is done by using inductors which inhibit a sudden change in current. Shorting is done by spark gaps, discharge tubes, zener-type semiconductors, and (MOVs), all of which begin to conduct current once a certain voltage threshold is reached, or by capacitors which inhibit a sudden change in voltage. Some surge protectors use multiple elements.
The most common and effective way is the shorting method in which the electrical lines are temporarily shorted together (as by a spark gap) or clamped to a target voltage (as by a MOV) resulting in a large current flow. The voltage is reduced as the shorting current flows through the resistance in the power lines. The spike’s energy is dissipated in the power lines or in the body of the MOV, converted to heat. Since a spike lasts only 10s of microseconds, the temperature rise is minimal. However, if the spike is large enough or long enough, like a nearby hit by lightning, there might not be enough power line or ground resistance and the MOV (or other protection element) can be destroyed and power lines melted.
Surge protectors for homes can be in power strips used inside, or a device outside at the power panel. Sockets in a modern house uses three wires: line, neutral and ground. Many protectors will connect to all three in pairs (line–neutral, line–ground and neutral–ground), because there are conditions, such as lightning, where both line and neutral have high voltage spikes that need to be shorted to ground.
Many have basic surge protection built in; these are typically clearly labeled as such. However, in unregulated countries there are power strips labelled as “surge” or “spike” protectors that only have a capacitor or RFI circuit (or nothing) that do not
provide true (or any) spike protection.