One wearing protective gear in conduit (4)
I believe the answer is:
pipe
'conduit' is the definition.
(I know that pipe is a type of tube)
'one wearing protective gear' is the wordplay.
'one' becomes 'i' (Roman numeral).
'wearing' indicates putting letters inside.
'protective gear' becomes 'PPE' (abbreviation for personal protective equipment).
'i' going inside 'ppe' is 'PIPE'.
'in' acts as a link.
(Other definitions for pipe that I've seen before include "Fluid or gas transporter" , "Hollow tube or musical instrument" , "Something in the organ loft" , "Tube; wind instrument" , "Wine cask; sing shrilly" .)