Bulb in contact with conductor of electricity (5)
I believe the answer is:
onion
'bulb' is the definition.
(onion is a kind of bulb)
'in contact with conductor of electricity' is the wordplay.
'in contact with' becomes 'on' (I've seen this in other clues).
'conductor of electricity' becomes 'ion' (an ion is an electrically charged particle).
'on'+'ion'='ONION'
(Other definitions for onion that I've seen before include "Head (slang); vegetable" , "Shape of Russian dome" , "Eye-watering vegetable" , "Cause of tears" , "Plant with edible bulb" .)