Factory worker under power line (5)
I believe the answer is:
plant
'factory' is the definition.
(a manufacturing plant)
'worker under power line' is the wordplay.
'worker' becomes 'ant' (worker is a type of ant).
'under' is a charade indicator (letters next to each other) (below, in a down clue).
'power' becomes 'p' (symbol in physics).
'line' becomes 'l' (used when specifying particular lines from a poem).
'p'+'l'='pl'
'ant' after 'pl' is 'PLANT'.
(Other definitions for plant that I've seen before include "Put in the ground to grow" , "Machinery; spy" , "Set; factory" , "eg Flower" , "Hide incriminating evidence" .)