live wire

noun2

1. •
   An electrical wire through which there is a flow of electrical current.

   • Two boys got electrocuted when a live wire fell on the auto-rickshaw in which they were sitting. — 2006
2. •
   (figurative) An especially energetic, alert, or vivacious person.

   • With his thin, eager face and darting hands he was more than a live wire - he was a whole bundle of live wires. — 1925