Mains
The mains were a critical engineering component in the function of refit Federation  starships that were associated with the ship's energizers.

During the battle between the  and  in 2285, the Enterprise took several phaser hits to the engineering section of the secondary hull forcing Captain Montgomery Scott "to take the mains off the line." Such a procedure was necessary due to the increased radiation that was flooding the engine room's adjacent reactor room. This left the ship to operate solely on impulse power.

Later, as the Enterprise attempted to escape the detonation of the Genesis Device, it was unable to engage warp drive due to having its mains still down. Once Spock made the necessary repairs the bring the mains back online, thus saving the ship. ()

Later that year, following the 's return flight to the 23rd century, Commander Pavel Chekov reported that the Klingon Bird-of-Prey's mains were down, and aux power was not responding. ()

See also  
 EPS mains

Propulsion technology