Optical Fibre Cables, Types, and Colour Coding
Optical fibre cables, their construction types and the 12-colour fibre code are tested through cable-selection scenarios and colour-counting questions.
Core rules
- Loose-tube cable: fibres in gel-filled tubes around a central strength member, with aramid yarn and HDPE sheath; good for outside plant. Tight-buffered cable is easier to connectorise indoors. Ribbon cable gives high fibre count and mass splicing.
- ADSS is all-dielectric for aerial use near power lines; figure-8 has a messenger wire; armoured cable uses steel tape for rodent and mechanical protection; LSZH sheath is for buildings.
- TIA-598 12-colour sequence: Blue, Orange, Green, Brown, Slate, White, Red, Black, Yellow, Violet, Rose, Aqua. The same sequence is used for fibres and for loose tubes.
- For 13–24 fibres, the sequence repeats with a black tracer; many cables use binder groups instead, so verify the datasheet and the printed legend.
- Store cable on a drum with the bend radius respected; cap ends to keep out water and dust.
Worked example
A 24-fibre cable uses the 12-colour sequence twice. Fibre 19: subtract 12 → position 7. The seventh colour is Red, so fibre 19 is Red with a black tracer. Fibre 12 is Aqua; fibre 13 is Blue with a black tracer.
Traps
- Counting from 0 instead of 1.
- Confusing Slate (grey) with White or Aqua with Green; use good light and the legend.
- Reading tube colour as fibre colour; record both.
- Assuming every 24F cable uses tracers: some use two binder groups with the same 12 colours.