the.com/live wire

means A person who's intensely energetic, alert, and lively — someone whose enthusiasm or unpredictability keeps everyone around them on their toes.

from Literal before it was figurative: a 'live wire' is an electrical wire still carrying current, dangerous to touch, humming with unseen power. The phrase jumped from engineering to people in the early 1900s, in the age when electricity itself was new and thrilling — calling someone a live wire borrowed that sense of crackling, barely-contained energy, the feeling that they might shock you if you got too close.