Hi !
It looks like CHARACTERISTIC is the answer.
CHARTER (let/letter) containing AC (electrical current) + IS (letterS, S short for IS) + TIC (nervous afliction).
Thank you, John from Arran - your explanation is much better. Like Big Dave, I was also unhappy about the wordplay that I gave, but it seemed close enough to possibly be right.
More haste, less speed should be my New Year's resolution.