An OM3 LC duplex patch cord carries two 50/125 µm laser-optimised multimode fibres, one per direction, with an LC connector at each end. The jacket is aqua by convention. It runs 10GBASE-SR optics to 300 m under IEEE 802.3 and also suits 25G links and existing OM3 plant. Radix Fibrotech makes each cord to order in Pune.
OM3 LC duplex cord specification
An OM3 LC duplex patch cord joins two 50/125 µm multimode fibres to an LC connector at each end. It serves 850 nm short-reach optics in racks, rows and equipment rooms, and OM3 is still common in installed 10G plant. Radix makes each cord to order in Pune, so one order line can combine any length, jacket and polarity from the table below. The LC connector guide describes the connector body.
| Parameter | OM3 LC duplex cord | Note |
|---|---|---|
| Fibre | 50/125 µm graded-index multimode, laser-optimised | Designed for VCSEL sources at 850 nm |
| Effective modal bandwidth | 2000 MHz·km at 850 nm | The cabling-standard figure that separates OM3 from OM2 |
| Fibre attenuation | 3.5 dB/km at 850 nm, maximum | A cord of a few metres adds almost nothing; connectors dominate the loss |
| Connector | LC, 1.25 mm ferrule, PC or UPC polish | There is no APC option for standard multimode LC |
| Jacket colour | Aqua | A TIA-598 convention; OM4 cords are often aqua too, so read the print |
| Cable | 1.6, 2.0 or 3.0 mm duplex zip, or round uniboot | Choose by space in the cable manager |
| Jacket rating | LSZH, PVC, riser or plenum | State the rating the site requires |
10G reach on OM3 and what it means for a cord
The figure most buyers ask about is the 10G reach. IEEE 802.3ae defines 10GBASE-SR at 300 m over OM3 and 400 m over OM4. Those limits apply to the whole channel, from transceiver to transceiver, including every panel, cassette and cord in the path. Add the length of both patch cords to the permanent link before comparing the total with 300 m.
| Application | Duplex LC optic | Published reach on OM3 | Published reach on OM4 |
|---|---|---|---|
| 10G Ethernet | 10GBASE-SR | 300 m | 400 m |
| 25G Ethernet | 25GBASE-SR | 70 m | 100 m |
| 16G Fibre Channel | 16GFC short-wave | 100 m | 125 m |
| 32G Fibre Channel | 32GFC short-wave | 70 m | 100 m |
Links at 40G and 100G over parallel optics use MPO connectors, not duplex LC, and belong with MTP and MPO patch cords. Fibre attenuation does not limit a short cord: at 3.5 dB/km, a 3 m cord loses about 0.01 dB. The number to watch is the loss of the two connectors, which is why a loss figure per connector is worth requesting on the quote.
When OM3 is still the right choice, and when to move to OM4
Choose OM3 when the cord has to match what is already installed or when the run is comfortably inside the limits above. Move to OM4 when the design needs the extra margin.
- Existing OM3 backbone. An OM3 cord matches the installed grade. An OM4 cord on an OM3 trunk costs more and does not extend the reach, because the channel follows its lowest grade.
- Short 10G runs. Most rack-to-rack and row links sit far inside 300 m, so OM3 gives the same result at a lower cord cost.
- 25G within 70 m. OM3 is enough for in-row and adjacent-row 25G.
- New backbone near the limit. If 10G runs approach 300 m, or 25G runs approach 70 m, the 400 m and 100 m OM4 figures give real margin. Choose OM4 for the trunk and cords together.
OM3 and OM4 share the 50/125 µm core, so the connectors mate with no core mismatch. The same is not true of 62.5/125 µm OM1, which loses heavily when joined to 50/125 µm fibre. The OM3 vs OM4 vs OM5 guide compares the grades in more detail.
Polarity of an OM3 duplex cord
A duplex link carries one fibre for each direction, so transmit at one device must land on receive at the other. A working duplex channel has an odd number of crossovers along its whole path. In a point-to-point link with no panels, one crossed (A-to-B) cord is the right part. In a channel with panels, cassettes and trunks, the crossovers add up, so check the channel design before settling the cord type.
Order A-to-B unless the design calls for A-to-A, and say so on the line. A cord with the wrong polarity does not damage the optics. The link stays down, and the usual cure is to swap the two connectors in one clip, then correct the A and B markings so the labels match the wiring. If a project mixes A-to-B and A-to-A cords, ask for each type to be bagged and labelled separately.
Length, diameter and routing
Measure the route a cord takes through the cable manager and add a small allowance for slack. Coiled excess blocks airflow and bends the fibre. Give a tolerance if the route is tight.
- 1.6 mm duplex cable saves space at a dense switch face.
- 2.0 mm is the common middle size and handles well.
- 3.0 mm suits longer, exposed runs.
- Uniboot puts both fibres in one round jacket with one boot.
Keep to the maker's stated minimum bend radius. If the rack has many tight turns, say on the quote that you want bend-insensitive multimode fibre. It is a specific order item and is not assumed.
Testing, inspection and cleaning
Multimode insertion loss is measured at 850 nm, and often at 1300 nm as well. Multimode loss readings depend on how light is launched into the fibre. A launch that meets the encircled flux requirement of IEC 61280-4-1 gives results that repeat between test sets and between labs, so ask for it if the report is used as acceptance evidence. End faces are inspected against IEC 61300-3-35 criteria.
State the maximum loss per connector you need and the report format when you request the quote. In service, dirt on the end face is the commonest cause of a failing multimode link. Inspect and clean both ends before every mating, and keep the dust caps on spare cords. The fibre loss budget guide shows how the cord figures enter a channel budget.
What to send us for a quote
Give one line per configuration, with:
- fibre grade (OM3) and bend-insensitive fibre if wanted
- cable diameter or uniboot, and jacket rating
- polarity: A-to-B unless stated
- length and tolerance
- the optics or panels at each end, so the grade can be checked
- maximum loss per connector and test report format
- label text and quantity for that line
Send the list through the request a quote page. Radix quotes against the specification and does not publish a price list. The basics shared by all LC cords are on the LC to LC patch cord page.
Questions buyers ask
What colour is an OM3 LC duplex patch cord?
Aqua is the usual jacket colour for OM3 under the TIA-598 convention. OM4 cords are often aqua as well and sometimes violet, so colour alone cannot identify the grade. Read the jacket print or ask for the test report.
How far can an OM3 LC duplex cord carry 10G?
IEEE 802.3ae gives 300 m for 10GBASE-SR over OM3, measured over the complete channel and not over one cord. Count every patch cord and permanent link in the path when you compare the total against that figure.
Can I connect an OM3 cord to an OM4 trunk?
Yes. Both use a 50/125 µm core, so the LC connectors mate without a core mismatch. Plan the channel to the lower grade, which here is OM3.
Can I join an OM3 cord to old 62.5/125 µm OM1 cabling?
Physically the connectors fit, but the 62.5 µm core is larger than the 50 µm core. Light passing from 62.5 into 50 µm fibre loses a large share, so avoid the mix. Match the cord to the installed core size.
Can I use an OM3 cord with a single-mode optic?
No. A single-mode optic such as 10GBASE-LR expects 9/125 µm OS2 fibre and is specified for that. Use an OM3 cord only with 850 nm multimode optics such as 10GBASE-SR.
Is there an APC version of an OM3 LC duplex cord?
Standard multimode LC cords are PC or UPC polished. The angled APC polish is a single-mode feature used to control reflection, and multimode optics do not need it.