The primary energy circuits were important energy-production components aboard Constitution-class starships.

In 2267, Lieutenant Commander Ben Finney sabotaged the primary energy circuits on the USS Enterprise, making it impossible to restart the ship's impulse engines. As the ship was in orbit of a planet and in danger of spiraling down to the surface, this would have resulted in the destruction of the ship. Fortunately, threatened with the death of his daughter, who had been brought aboard the ship, Finney relented and informed Captain Kirk where he had sabotaged the circuits, allowing Kirk to reverse the damage. (TOS: "Court Martial")