Good conductor or policeman (6)
I believe the answer is:
copper
I believe this clue is a double definition.
'good conductor' is the first definition.
(I've seen this in another clue)
'policeman' is the second definition.
(copper can informally mean a police officer)
'or' is the link.
(Other definitions for copper that I've seen before include "Police officer (slang)" , "Metallic element and British bobby" , "Element; butterfly" , "English policeman" , "Reddish metallic element" .)