(A+) a strip of metal inside
the metal strip or anything for that matter that goes at the bottom of doorways is called a threshold.
That can be the carpet edging strip, the fastening strip, carpet plating strip for a few names.
To determine if a fuse is blown, visually inspect the fuse for a break in the metal strip inside. If the metal strip is broken, the fuse is blown and needs to be replaced.
a bimetallic strip
If you have access to the fuse box, take the fuse out and look at it. An intact fuse will have a visible, unbroken, metal strip running between the terminals. A blown fuse will have a broken metal strip on the inside and usually will be visibly discolored on the inside.
It is called a blown fuse.
Metal strip inside fuse will be broken or burnt
You are describing a fuse. Fuses are protective devices used in electrical circuits to prevent damage from excessive current. When the current exceeds a safe level, the metal strip inside the fuse melts, breaking the circuit and stopping the flow of electricity.
The simple term for it is Schleutter strip. There are several variations, but genericaly that is what its called.
The essential component of a fuse is a metal strip that or wire that melts when too much current flows through it.
a fuse