OM1 Fiber: Legacy Reach in Metres, Not Kilometres
Quick answer / TL;DR: Short answer: OM1 carries 1G to about 300 m and 10G to about 33 m. Do not specify it for new work; use OM4 or single mode instead. Buy OM1 only to match an existing installation, and expect to replace it when the link needs 10G beyond 33 m.
Fiber cords: two connector families, two fiber types, three polish options.OM1 is 62.5 micron multimode fibre with a 200/500 MHz-km bandwidth rating. It was the default indoor fibre for years and remains common in older buildings.
Its limits are short by modern standards but adequate for many links that already exist.
Reach by Speed
| Speed | OM1 | Note |
|---|
| 100 Mbps | 2,000 m | Legacy |
| 1G | 300 m | Typical ceiling |
| 10G | 33 m | Short only |
| 40G | Not supported | – |
The 10G figure is the one that decides upgrades: most horizontal runs exceed 33 m, so OM1 cannot carry 10G to the desk.
Where It Still Makes Sense
- Matching existing OM1 patch panels
- Short rack-internal links
- Legacy equipment with 62.5 micron optics
- Temporary links during migration
Mixing OM1 with OM3 or OM4 works in one direction only: the link performs to the lower grade.
Real-World Applications
A 2005 office with OM1 backbone at 1G can keep running until the 10G refresh, at which point the cable is replaced rather than re-used. A short rack link within 30 m can stay on OM1 indefinitely.
Standards and Verification
| Reference | Relevance |
|---|
| ISO/IEC 11801 | OM categories |
| IEC 60793-2-10 | Multimode fibre |
| IEEE 802.3 | Reach by PHY |
Measured bandwidth of an installed fibre is not provided in the knowledge base. Test the link before planning an upgrade.
References
- ISO/IEC 11801-1, Generic cabling
- IEC 60793-2-10, Optical fibres – Multimode
- IEEE 802.3, Ethernet reach by PHY
Practical Notes
Label the fibre grade at every panel. A 10G plan built on unlabelled OM1 fails at commissioning.
Related reading: fiber cable — blogs/news/fiber-cable
Related reading: powered fiber cable — blogs/news/powered-fiber-cable
Related reading: om5 fiber cable — blogs/news/om5-fiber-cable
Frequently Asked Questions
How far does OM1 do 10G?
About 33 m.
Should I install OM1 today?
No. Use OM4 or single mode.
Can OM1 mix with OM4?
Yes, at the lower grade's performance.
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