Fiber Optic Cable Types, Construction and Colour Coding
Fiber Optic Cable Types, Construction and Colour Coding
This domain tests cable selection and identification: tight-buffered versus loose-tube, indoor versus outdoor, armored, ADSS and drop cable, plus the 12-fiber colour sequence used in trays and buffer tubes.
Core rules and concepts
- Tight-buffered cable has a 900 µm buffer directly on the fiber; it is flexible and suits indoor patch cords and short runs. Loose-tube cable places 250 µm fibers in gel-filled tubes around a central strength member; it suits outdoor ducts and aerial spans.
- Strength members carry tension: aramid yarn in many indoor cables, steel or FRP rods in outdoor cables. Armored cable adds a metal tape for rodent and crush protection; ADSS is all-dielectric and used on power lines.
- Ribbon cable has fibers bonded in a flat matrix, allowing mass splicing. Drop cable is a small flat cable used from a distribution point to a subscriber.
- The standard 12-fiber colour code is Blue, Orange, Green, Brown, Slate, White, Red, Black, Yellow, Violet, Rose, Aqua. Buffer tubes usually follow the same order, and a second group may repeat with tracers or a different binder.
Worked example
A 24-fiber loose-tube cable has two 12-fiber tubes. Tube 1 is blue and tube 2 is orange. You need fiber 19. Count within tube 2: fiber 13 is blue, 14 orange, 15 green, 16 brown, 17 slate, 18 white, 19 red. The fiber is the red fiber in the orange tube. This is why counting must start at the first fiber, not at zero.
Traps that cost marks
Slate is not grey and aqua is not turquoise in the standard sequence. Do not count from the wrong end of a tube. Do not use indoor tight-buffered cable as a direct-buried outdoor cable. Do not cut aramid yarn as if it were a fiber; it is a strength member.