Electrical safeguard (4)
I believe the answer is:
fuse
'electrical safeguard' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for fuse that I've seen before include "Mix together" , "Coalesce, melt together" , "Unite by melting" , "Safety device in circuit" , "Join, coalesce" .)