An electrical device including a PTC conductive polymer sheet, and first and second electrodes physically contacted with opposite surfaces of the conductive polymer sheet is disclosed. The first and second electrodes have a plurality of protrusions protruded from surfaces thereof, respectively. The protrusions have an surface roughness (Rz) of 1 to 20 m and an average width ({overscore (Rw)}) which is 0.5 to 2 times of the surface roughness (Rz), and an average gap ({overscore (Rg)}) between adjacent protrusions is 0.5 and 2 times of the surface roughness (Rz). The conductive polymer sheet has a thickness which is more than 5 times of the surface roughness (Rz).