The optical cable design is a 6-core optical cable from the machine room to the optical node, of which 3 cores are redundant. Common fiber cores include 1 core, 2 cores, 6 cores, 8 cores, etc. Imm (main cord) Material Stainless Steel Color Silvery White UL94 V-0 (*Burning stops within 10 seconds on a veritcal specimen, no drips of flaming particles. Specifications are correct at time of printing and subject. For example, if you have three optical fiber access switches, you need to have three cores. Understanding Fiber Cores: Core: The central glass fiber that transmits light signals.