Lead: At 5:15 PM on November 9, 1965 most of the northeastern United States went dark. The cause? Not a terrorist attack. Not incompetent workers. Not a huge natural disaster. The great blackout was caused by a small metal relay doing exactly what it was supposed to do.

Intro: A Moment in Time with Dan Roberts.

Content: The powergrid of a modern industrial nation is a highly complex and intricate creation. Different regions demand power at different levels at different times. As a result power is often consumed at great distances from the place it is generated. One city may have a huge demand at the same time that another's requirement is relatively meager. The power network is set up to divert surplus electricity from light demand areas to those where the needs are greater.