Motivation limits current working (8)
I believe the answer is:
ambition
'motivation' is the definition.
'limits current working' is the wordplay.
'limits' becomes 'ambit' (I've seen this before).
'current' becomes 'i' (symbol for electric current).
'working' becomes 'on'.
'ambit'+'i'+'on'='AMBITION'
(Other definitions for ambition that I've seen before include "Desire to achieve success" , "Desire to get on" , "Target" , "Objective" , "hope for the future" .)