Fibre Optic Cable Selection Guide: OM3, OM4, OM5 or Single Mode
Fibre optic cabling carries the links that copper cannot: building backbones, campus connections, data-centre spines and FTTH networks. Choosing it means answering five questions – multimode or single mode, which grade, which cable construction, which connectors and which distribution hardware. This guide walks through each one and links to the matching TMT Global fibre optic products.
1. Multimode or single mode?
| Multimode (OM2–OM5) | Single mode (OS2) | |
|---|---|---|
| Core size | 50 µm | 9 µm |
| Typical distance | Up to a few hundred metres | Kilometres |
| Light source | Low-cost 850 nm VCSEL transceivers | 1310/1550 nm laser transceivers |
| Typical use | Inside buildings and data centres | Campus links, telecom, FTTH, long backbones |
Rule of thumb: inside one building or data hall, multimode keeps transceiver costs low. Between buildings, for FTTH, or wherever the distance may grow, choose single mode. Many projects run both: multimode in the risers and single mode for the incoming service and campus links.
2. Which multimode grade?
| Grade | Jacket colour (typical) | 10 Gb Ethernet | 40/100 Gb (short-reach) | Best for |
|---|---|---|---|---|
| OM2 | Orange | About 82 m | Not recommended | 1 Gb links and extending existing OM2 systems |
| OM3 | Aqua | 300 m | 100 m | Building backbones, 10 Gb uplinks |
| OM4 | Aqua or violet | About 400 m | 150 m | New backbones and data centres – the usual choice today |
| OM5 | Lime green | About 400 m | 150 m, plus wideband multiplexing | High-speed data centres using short-wave multiplexing |
For new installations, OM4 is the safe default for multimode. Keep cable, patch cords and pigtails the same grade – mixing grades limits the link to the weakest part.
3. Cable construction: indoor, outdoor, armoured or FTTH
- Indoor (tight-buffered, LSZH) – flexible and easy to terminate for risers, trays and comms rooms. Choose LSZH where the specification calls for low-smoke cable in public buildings.
- Indoor/outdoor (loose tube) – gel-filled or dry tubes protect fibres from moisture and temperature changes for ducts between buildings.
- Armoured – corrugated steel tape protects against rodents and crushing for direct burial and harsh routes.
- FTTH drop (G.657) – bend-insensitive single-mode fibre that tolerates tight corners in apartments and villas.
Fibre count: each link normally uses two fibres (transmit and receive). Count the links you need today, double it for growth, and round up to a standard count – 6, 8, 12, 24, 48 and higher. Fibre is cheap compared with pulling a second cable later. See the multi-core fibre cable guide for more detail.
4. Connectors and polish: LC or SC, UPC or APC?
- LC – small form factor, the standard for switches, SFP transceivers and high-density patch panels.
- SC – larger push-pull connector, common in FTTH, ODFs and telecom equipment.
- UPC (blue on single mode) – the normal polish for data networks.
- APC (green) – angled polish with very low back-reflection, used in PON/FTTH and RF video. Never mate APC with UPC – the angles do not match and the link will fail or be damaged.
Match connectors with the right fibre adapters and patch cords; our guides on SC APC vs SC UPC, OM3, OM4 and OS2 patch cords go deeper.
5. Termination and distribution hardware
- Optical distribution frames (ODF) and fibre patch panels terminate incoming cables in the comms room.
- Pigtails are spliced onto each fibre to give a factory-made connector.
- PLC splitters divide one feed into many outputs for PON/FTTH.
- Splice closures and wall boxes protect joints and drops along the route.
Budget the link loss
Every link has a loss budget set by the transceivers. Add up the loss of the fibre, every connector pair and every splice, and keep a safety margin. Typical planning values are about 3.5 dB/km for multimode at 850 nm, about 0.4 dB/km for single mode at 1310 nm, roughly 0.3–0.75 dB per mated connector pair and around 0.1 dB per fusion splice. Splitters add more – check the insertion loss on each splitter’s datasheet. Always test and record every link after installation.
Frequently asked questions
Is single mode more expensive?
The cable costs about the same; the difference is mainly in the transceivers. For long or future-proof links, single mode is often cheaper over the life of the building.
Can I connect OM3 and OM4?
They are compatible (both 50 µm), but the link performs only to the OM3 level.
How many spare fibres should I install?
At least 50–100% spare on backbones. Pulling a new cable later costs far more than the extra fibres.
Related TMT Global guides
Get a fibre design and quotation
Send us your riser diagram or site plan and we will propose the fibre type, counts, termination and patching, with datasheets for approval. Contact TMT Global.