In general, you can calculate the required number of cores as: �� (Total number of equipment interfaces × 2) + 10–20% spare fibers for backup. If the devices use serial communication or equipment multiplexing, the number of cores can be reduced accordingly. The number of. Common fiber cores include 1 core, 2 cores, 6 cores, 8 cores, etc. The total number of cores for a 1pc fiber patch cable is calculated as the number of. Fiber optic cables consist of multiple thin strands of glass or plastic, known as “cores. ” These cores carry the data signals via light.