This course examines the causes of overvoltage conditions on distribution systems, including those that occur during switching operations and those that occur due to natural events such as lightning. The consequences of overvoltage events—including safety, deterioration of equipment, and the impact to customer service—are discussed. The different types of lightning arresters (surge arresters) are detailed, along with specific examples of their application to the distribution system. This course ends with a discussion of insulation coordination and includes both basic impulse and chopped wave tests.