A simple rule is that each device needs two cores—one for sending and one for receiving data. The total number of cores for a 1pc fiber patch cable is calculated as the number of branches multiplied by the number of cores per branch (if there are no branches, the number of branches = 1). Of course, this is a general situation, and specific words may consider according to the following criteria. Number of wiring points and switches. Single-mode: A. This guide walks you through the simple decision steps engineers use, the common strand counts on the market, and clear rules-of-thumb for different project types so you choose a cable that fits both today's needs and tomorrow's growth.