Protecting load devices from the effects of low-side surges

Wherever lightning and poor utility power system grounds exist, distribution secondary systems are subjected to high-voltage surges due to lightning current seeking ground through low-voltage circuits. The authors describe this low-side surge phenomenon, and the importance of protecting the service entrance and critical load devices properly, especially when secondary arresters are applied on distribution transformers. This practice can increase the voltage stress at the customer service entrance. If any ground paths exist on the customer side of the service entrance, these surges can penetrate further into the customer´s system. Damage caused by low-side surges can be avoided if properly coordinated arresters are installed at the transformer secondary, service entrance, and at load devices. A properly coordinated and effective MOV protection scheme is described and recommended