More competent section of a cable-run (5)
I believe the answer is:
abler
'more competent' is the definition.
('able' can be similar in meaning to 'competent')
'section of a cable-run' is the wordplay.
'section of' indicates the answer is hidden within the clue.
'ABLER' is hidden within 'a cable run'.
(Other definitions for abler that I've seen before include "Showing more skill" , "The better" , "fitter" , "More skilled" , "Increasingly smart" .)