Safety device from America with iron casing (4)
I believe the answer is:
fuse
'safety device' is the definition.
(electronic safety device)
'america with iron casing' is the wordplay.
I cannot really see how this works, but
'america' could be 'us' (United States) and 'us' is found in the answer.
'iron' could be 'fe' (Fe is the chemical symbol for iron) and 'fe' is located in the leftover letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'from' is the link.
Can you help me to learn more?
(Other definitions for fuse that I've seen before include "Meld" , "Join or blend to form an entity" , "Unite by melting" , "Join, coalesce" , "Melt; ignition device" .)