Person left inside doing electrical work (9)
I believe the answer is:
earthling
'person' is the definition.
(earthling is a kind of person)
'left inside doing electrical work' is the wordplay.
'left' becomes 'l' (common abbreviation).
'inside' indicates putting letters inside.
'doing electrical work' becomes 'earthing'.
'l' placed inside 'earthing' is 'EARTHLING'.
(Other definitions for earthling that I've seen before include "sci-fi character" , "Human being (sci-fi)" , "man so to be called from space?" , "Man of the world" .)