Field guide · Cabling & low-voltage
Fibre Types, Connectors and Polish
Optical fibre is identified by colour on site the same way copper is: an aqua jacket means something specific and a green connector body means something you must not ignore. Covers OM1 through OM5 and OS2 with their jacket colours and real supported distances, the connector families you will actually meet, and the UPC/APC distinction that quietly kills links.
Diagram
Read the jacket, read the connector, don't mate blue to green.
Identify by
What the cable is, from its colour and print.
| Jacket | Type | Mode | Core | 10 Gb | 40/100 Gb |
|---|---|---|---|---|---|
| orange | OM1Legacy. You will meet it in buildings cabled in the 1990s and you should not install it. Its larger core makes it incompatible in practice with the 50 µm types — mixing them in one channel costs you several dB at the joint. | multimode | 62.5 / 125 µm | 33 m | — |
| orange | OM2Also legacy, and confusingly the same jacket colour as OM1 despite a different core. If a run is orange, read the print on the jacket rather than assuming which one it is. | multimode | 50 / 125 µm | 82 m | — |
| aqua | OM3The first laser-optimised multimode, and the point at which aqua starts meaning something useful. A sensible minimum for any new multimode backbone. | multimode | 50 / 125 µm | 300 m | 100 m |
| aqua / violet | OM4The normal choice for a modern multimode backbone. Jacket is usually aqua, which makes it indistinguishable from OM3 at a glance — some manufacturers use violet specifically to solve that, but it is a convention rather than a standard. | multimode | 50 / 125 µm | 400 m | 150 m |
| lime | OM5Wideband multimode, designed for short-wavelength division multiplexing. It buys you more lanes on one pair of fibres rather than more distance, so it only pays off with optics that use it. | multimode | 50 / 125 µm | 400 m | 150 m |
| yellow | OS2Single-mode. The cable is cheaper than OM4; the optics are not, which is the whole trade-off. For campus links, risers over a few hundred metres, or anything you want to still be adequate in fifteen years, this is the answer. | single-mode | 9 / 125 µm | 10 km with LR optics, 40 km with ER | 10 km |
Colour identifies the type at a glance and should never be the last word — OM3 and OM4 are both aqua, and OM1 and OM2 are both orange despite different cores. The jacket print is the authority.
Questions
Questions people actually ask
- What is the difference between OM3 and OM4?
- Both are 50 µm laser-optimised multimode and both are usually aqua. OM4 carries 10 gigabit to 400 metres against OM3's 300, and 40 gigabit to 150 metres against 100. Because the jacket colour is often identical, read the print on the cable rather than trusting the colour.
- Single-mode or multimode?
- Multimode is cheaper to light and fine inside a building. Single-mode costs more in optics and almost nothing more in cable, and it removes distance as a consideration entirely. For campus links, long risers, or anything meant to outlast two refresh cycles, single-mode is the one that does not need revisiting.
- Can I connect a UPC connector to an APC connector?
- No. APC endfaces are angled 8° and UPC are flat, so the two cannot touch across the core. You get a large air gap, heavy reflectance, and a link that is degraded or dead — and forcing them damages both ferrules. Blue to blue, green to green.
- What colour is fibre optic cable?
- Under TIA-598: orange for OM1 and OM2, aqua for OM3 and OM4, lime green for OM5, and yellow for single-mode. Some manufacturers use violet for OM4 to tell it apart from OM3, but that is a convention rather than part of the standard.
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