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| Figure 12-1 Elementary lightning or surge arrester. |

| (approximately 2 inches for each 1,000 V of arrester rating). The pellets, from 1/8 to ¼ inch in diameter are made of lead peroxide (PbO2) coated with litharge (or lead oxide, PbO). The series gap assembly is usually located at the top end, where it is subject to spring pressure; one end of the gap assembly is connected to the line and the other to the pellets, with its connection to ground coming from the bottom of the pellet column. Though rapidly becoming obsolete, many arresters of this type still exist and will be around for a long time. |

| When there is an excessive voltage surge on the line, the spark jumps across the gap or gaps and flows through the pellets through multiple paths to ground, heating the pellets along the way. Under normal temperatures, lead peroxide is a relatively good conductor of electricity. When heated, it turns to lead oxide or litharge, which is a very poor conductor. As the surge voltage is drained to ground, a sealing action takes place at the contact surfaces of the pellets in the path of the discharge current, the lead peroxide changing to lead oxide or litharge. This chemical reaction restores the pellet column to its nonconducting state for normal line voltages. |

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