This thread may be dead(?), but I was just re-watching "The Doomsday Machine" and a line stood out (in regard to TWOK's
"The main energizer's out!" from Scotty and to the whole reactor issue):
Communications officer Palmer to Spock right after the Planet Killer has knocked down the Enterprise's shields: "Sir, deck seven reports power failure in main energizers. Implementing emergency procedures."
And looking through the transcripts turns up this from Masters in "The Alternative Factor": "The energizer has shorted. Get out of here. Sound the alarm."
However, the relationship between reactor(s) and energizer(s) seems to remain unclear.