A surge arrester is a device that protects electrical power systems from damages caused by lighting. A typical surge arrester has both a ground terminal and a high-voltage terminal. When a powerful electric surge travels from the power system to the surge arrester, the high voltage current is sent directly to the insulation or to the ground to avoid damaging the system. Lightning and Electrical Surges When a powerful surge or a lightning strikes a particular electrical system, it damages the whole system and any electrical devices connected to the system. Electrical devices work at a certain voltage range. When these devices receive a voltage way higher than the specified voltage sufficient for their operation, they blow up or get damaged. However, electrical systems that are protected by a surge arrester do not get damaged, because the arrester ensures that the high voltage does not get into the electrical system. Diverting Lighting and Electrical Surges Using MOV The surge arrester does not absorb all of the high voltage that passes through it. It simply diverts it to the ground or clamps it to minimize the voltage that passes through it. The secret to the arrestor’s success in diverting lightning or high electrical surges is the MOV or the Metal Oxide Varistor. MOV is a semiconductor that is highly sensitive to voltage. At normal voltages, the MOV works as an insulator and does not allow current to pass through. But at high voltages, the MOV acts as a conductor. It works as a switch that is open when there is a standard AC voltage, and a switch that is closed when lightning or high voltage is present. What Causes Electrical Surges Electrical surges occur when an incident increases the electrical charge running through a power line at some point. The most popular cause of a surge is lightning. However, lightning causes electrical surges only every once in a while. During a lightning storm, lightning may strike somewhere near a power source and affect the voltage running through a power line. Sometimes, the best way to protect an electrical device from the effects of a lightning surge is unplugging it from the power source. A surge arrestor may not work 100 percent of the time because lightning can produce very high voltages that even surge arresters cannot fully handle. More often than not, electrical devices that rely on high electrical power cause electrical surges (e.g. refrigerators and elevators). The operation of these devices sometimes causes a sudden demand for electricity that upsets the flow of current in an electrical system. Even if these surges do not cause as much damage as a lightning surge, they can still inflict major damage to some electrical devices connected to the electrical system. Installing Surge Arrestors Surge arrestors are usually installed near an electric meter to protect the electrical system of a home or building from the effects of power surges coming from the outside. A surge arrestor can protect other electrical equipment connected to the power source, but may not provide total protection against surges that come from faulty wiring or the overall electrical functioning of household or office electrical appliances.