Litech Insights

Open any loose-tube fibre optic cable and you will find a rainbow of coloured tubes, each holding a bundle of coloured fibres. Those colours are not decoration. They follow a standard code that tells a splicer exactly which fibre is fibre number 1, which is fibre number 37, and which one goes to which customer. Get the code wrong and a link is spliced to the wrong port, which can take hours to trace. This guide explains the standard fibre optic colour code, how tube and fibre colours work together in high-count cables, and what the jacket and connector colours on patch cords mean.

The standard: TIA-598 colour code

The most widely used fibre colour code is ANSI/TIA-598 (Optical Fiber Cable Color Coding). It uses twelve colours in a fixed order. The same twelve colours, in the same order, are used for the fibres inside a tube and for the tubes inside the cable:

Fibres 13 to 24 repeat the same twelve colours with a black stripe or dashed mark (a "tracer"). Fibre 20 is the exception: because a black stripe would not show on a black fibre, it gets a yellow tracer instead. Some manufacturers use a ring mark rather than a stripe, but the idea is the same.

A handy way to remember the first six is to learn them in pairs: blue, orange, green, brown, slate, white, which is also the order used for copper telephone and LAN pair colours. The second six are red, black, yellow, violet, rose, aqua.

How tube and fibre colours work together

In a loose-tube cable, each tube usually holds 12 fibres (some smaller cables use 2, 4, 6 or 8 per tube). To identify a fibre you read two colours: the tube colour first, then the fibre colour. With 12 fibres per tube:

This is how a 144-fibre cable stays manageable: 12 tubes of 12 fibres, and every fibre has a unique tube and fibre colour pair. In larger cables, tubes 13 to 24 repeat the colours with a stripe, just like the fibres.

Worked example: finding fibre number 30

You are told to splice fibre 30 of a 48-fibre cable with 12 fibres per tube. Divide by 12: fibres 25 to 36 are in the third tube, which is green. Fibre 30 is the sixth fibre in that tube (30 minus 24), so it is the white fibre in the green tube. In the same way, fibre 7 is the red fibre in the blue tube, and fibre 44 is the black fibre in the brown tube.

If the cable uses 6 fibres per tube, the answer changes: fibre 30 is then the sixth fibre in the fifth tube, the white fibre in the slate tube. That is why you must always check how many fibres each tube carries before you start. Our guide to choosing the right fibre count explains common tube layouts from 2F to 144F.

Filler rods and where to start counting

Stranded loose-tube cables, such as duct, direct buried and ADSS cables, often contain filler rods to keep the cable round when there are fewer tubes than positions. Fillers are usually solid and black or natural (uncoloured), and they carry no fibre, so do not count them.

Because the tubes are wound in a helix, there is no fixed "top" of the cable. Find the blue tube (tube 1), then follow the colour order (orange, green, brown and so on) around the cable to number the rest. Many cables also show the direction of counting in their datasheet or with a marked tube.

Jacket colours on indoor cables and patch cords

For indoor cables and patch cords, the outer jacket colour tells you the fibre type at a glance. TIA-598 recommends these colours for premises cable:

Outdoor cables, such as aerial Fig-8, micro duct and FTTH drop cable, almost always have a black jacket because black polyethylene resists sunlight. On these cables, read the print on the jacket (fibre type and count) rather than relying on colour.

Connector colours: blue, green, beige and aqua

Connector bodies are colour coded too, and this matters even more than the jacket, because mating the wrong connectors causes high loss and can damage the end faces:

The most common mistake in the field is plugging a green APC connector into a blue UPC adapter. They fit mechanically, but the angled and flat end faces do not touch properly, giving several dB of loss and a poor return loss. Hybrid cords such as an SC/UPC to SC/APC patch cord exist exactly for joining the two. Our patch cord guide explains UPC and APC in more detail.

Other colour codes you may see

TIA-598 is the most common code, but it is not the only one. Some manufacturers and some national operators use their own order, and some older or regional standards (for example, schemes based on IEC 60304) start with different colours. A few cable makers also print numbers on the tubes instead of, or as well as, using colours. Before you splice an unfamiliar cable, check its datasheet or test report for the colour sequence and fibres per tube, and write the sequence on your splice plan.

Practical tips for splicers and installers

• Match colour to colour at every joint. On a straight-through joint, blue goes to blue and orange to orange, tube by tube. It keeps fibre numbering the same from end to end.
• Work in good light. Slate and white, and rose and red, are easy to confuse in a dim manhole or at dusk. A head torch with white light helps.
• Clean off gel carefully. Gel-filled tubes can smear colour coatings. Use a proper gel cleaner and lint-free wipes, then check each colour again before splicing.
• Keep a splice record. Note the tube colour, fibre colour, tray and splice number for every joint. It saves hours when a fault appears later.
• Prove the result. After splicing with a fusion splicer such as the INNO i4S, an OTDR test with the EXFO MaxTester 715B confirms each fibre is continuous and in the right order. See our fusion splicing guide and OTDR testing guide.

In short: fibres and tubes follow the same twelve-colour order (blue, orange, green, brown, slate, white, red, black, yellow, violet, rose, aqua). Read the tube colour first, then the fibre colour. Yellow jackets mean single-mode, orange means OM1 or OM2, aqua means OM3 or OM4, and a green connector means APC.

Frequently asked questions

What is the colour of fibre number 1?

Under TIA-598, fibre 1 is blue, fibre 2 is orange and fibre 3 is green. The first tube in a loose-tube cable is also blue.

What colour is fibre 13?

Fibre 13 is blue with a black stripe or mark. If the cable has 12 fibres per tube, fibre 13 is instead the plain blue fibre in the second (orange) tube.

What does a yellow fibre cable mean?

A yellow jacket on an indoor cable or patch cord means single-mode fibre (OS1 or OS2). It is the type used for FTTH, telecom and long-distance links.

Why is my outdoor fibre cable black?

Black polyethylene resists ultraviolet light and weather, so almost all outdoor cables are black regardless of the fibre type inside. Check the jacket print to see the fibre type and count.

Can I connect a green connector to a blue one?

No. Green means APC (angled) and blue means UPC (flat). Mating them causes high loss and can damage both end faces. Use a hybrid UPC to APC patch cord instead.

Need fibre cable or patch cords?

Litech manufactures single-mode optical fibre cables for duct, direct buried, aerial and FTTH routes, and supplies single-mode and multimode patch cords including SC/APC, OM1, OM4 and OM5 cords, plus fusion splicers and EXFO test equipment. Message us on WhatsApp +92 313 7776766 for a quotation. Delivery is free across Pakistan.

Sources: ANSI/TIA-598-D, Optical Fiber Cable Color Coding; ISO/IEC 11801 (OM1 to OM5 and OS1/OS2 fibre categories).