An unprecedented security cover has been thrown across politically sensitive Nandigram with 15,000 central forces deployed to man just 176 polling booths ahead of the assembly by-poll on Monday. District Magistrate and Returning Officer Choten Dhudup Lama said 7 companies (each company 1000) of BSF and 8 companies of CRPF have been deployed in Nandigram I and Nandigram II blocks, which translated into 85 central force personnel per booth.