An MTP-12 OM4 trunk cable is a 12-fibre, 50/125 µm multimode cable with an MTP connector at each end, installed as the permanent link between cassettes or panels. It is ordered by polarity type (A, B or C), female or male pinning at each end, and exact length. Radix Fibrotech terminates each trunk to the length on your drawing.
What an MTP-12 OM4 trunk cable is
An MTP-12 OM4 trunk cable carries twelve 50/125 µm fibres in a single row, terminated at each end in a 12-fibre MTP connector. It is the fixed part of a link: pulled in once between two patch fields, with the equipment cords moved around it. A buyer searching for an mtp 12 fibre om4 trunk cable usually wants this item: one connector per end, an aqua jacket by convention, and a length that fits the building.
MTP is the brand name for an enhanced MPO connector with a floating ferrule. It mates with standard MPO parts, so the choice between the two names rarely changes the drawing. The wider family of backbone assemblies is described on the MPO trunk cables page; this page covers the 12-fibre OM4 case in detail.
Why OM4 on a 12-fibre trunk
OM4 is a 50/125 µm laser-optimised multimode fibre with a modal bandwidth of 4700 MHz·km at 850 nm, against 2000 MHz·km for OM3. The extra bandwidth is what lengthens the reach of 850 nm optics. IEEE 802.3 gives these channel limits on OM4:
| Application | Fibres used of the 12 | OM4 channel reach |
|---|---|---|
| 40GBASE-SR4 | 8 | 150 m |
| 100GBASE-SR4 | 8 | 100 m |
| 10GBASE-SR through duplex cassettes | 2 per channel, up to 6 channels | 400 m |
| 25GBASE-SR through duplex cassettes | 2 per channel, up to 6 channels | 100 m |
SR4 optics transmit on fibres 1 to 4 and receive on fibres 9 to 12, so the four middle fibres of a 12-fibre trunk stay dark on a direct parallel link. That is normal and costs nothing, but it is a reason some designs use 8-fibre or 24-fibre trunks instead. Reach figures cover the whole channel including every mated pair, so run the numbers in the fibre loss budget guide before fixing the length.
Polarity on a 12-fibre trunk: Type A, B and C
Polarity decides which fibre position at one end lands on which position at the other. TIA-568.3 describes three array methods, and the trunk type must match the cassettes and cords around it.
| Type | Key orientation, end to end | Fibre mapping | Where it is used |
|---|---|---|---|
| A | Key up at one end, key down at the other | Position 1 to 1, 12 to 12 | Channels that put a pair-flipped patch cord at one end |
| B | Key up at both ends | Position 1 to 12, 12 to 1 | Direct parallel links and Method B cassette channels |
| C | Key up at one end, key down at the other | Pairs flipped: 1 to 2, 2 to 1, 3 to 4, 4 to 3 | Channels built from duplex pairs through cassettes |
Changing polarity after the trunk is pulled means replacing it, or adding a cord that corrects it. Send the channel diagram with the order, or read the MPO polarity guide first.
Female and male pinning
Two mated MPO connectors need exactly one pinned (male) and one unpinned (female) connector. The pins keep the two ferrules aligned. Match the trunk to the hardware at each end:
- Cassette or adapter panel. The connector inside the cassette is commonly pinned, which makes the trunk end female.
- Transceiver port. The MPO receptacle in an SR4 module is commonly pinned, which makes the patch cord end female.
- Trunk joined to a second trunk. One end of the join is male and the other female, with the adapter between them.
These are common arrangements, not a rule. Read the cassette and module datasheets, because a wrong gender cannot be mated without replacing a connector. Changing pins on site also risks the end face, so order the gender you need.
Cutting the trunk to row or room length
A factory-terminated trunk cannot be shortened on site, so the length has to be right on the order. Measure the route through the containment, not the straight line, and add slack for dressing at each rack. A measured route of 18 m with 1 m of slack at each end becomes a 20 m order length, plus the leg lengths at the connectors.
For a room with several rows, list each row as its own line with its own length. Give the tolerance you can accept, since a trunk that is short cannot be fixed. If the cable has to pass through existing conduit, state the outer diameter limit and the tightest bend on the route. Ask for a pulling grip on any run longer than a single rack, so the load goes onto the cable strength members and not the connectors.
Jacket options are LSZH for occupied buildings, riser or plenum for North American fire codes, and armoured construction for crush or rodent risk.
What to send us for a quote
- Fibre count (12) and quantity for each length.
- Grade: OM4 50/125 µm, and bend-insensitive fibre if you want it.
- Connectors: MTP or MPO, and female or male at each end.
- Polarity: Type A, B or C, with the channel diagram if you have it.
- Length for each line, with tolerance and pull-grip requirement.
- Jacket: LSZH, riser, plenum or armoured, plus colour and outer diameter limit.
- Marking: label text at each end and the cable print.
- Test report format and the maximum insertion loss per mated pair.
Send the list through the quote request form, or email sales@radixfibrotech.com. Radix works to your drawing and bill of materials, so a marked-up sketch is enough to start.
Before you plug it in
Inspect both end faces before mating, even when the connector caps are on. Dust on one fibre in a 12-fibre ferrule affects only that fibre, which makes a bad link hard to trace later. Clean with a tool made for MPO ferrules and look again. Test the installed channel at 850 nm and compare it against the factory report for that trunk. A large difference usually points to contamination or a damaged connector, not to the cable.
Questions buyers ask
How many fibres does a 40G or 100G SR4 link use on an MTP-12 trunk?
Eight. Fibres 1 to 4 transmit and fibres 9 to 12 receive, so the four middle fibres stay unused on a direct parallel link. Through a duplex cassette the same trunk carries up to six LC channels instead.
Which polarity should an MTP-12 OM4 trunk be?
It depends on the method used by the cassettes and cords at each end. Type B is common for direct parallel links, and A or C appear in cassette channels. If you are unsure, send the channel diagram and we will confirm the type before the order is placed.
Should the trunk be female at both ends?
Often, because cassettes and transceivers commonly present pins. Check the datasheet of each device the trunk plugs into. One pinned and one unpinned connector are needed for every mated pair.
Can an MTP-12 trunk be shortened on site?
No. The ferrule is polished at the factory and the fibres are fixed in the connector. A trunk that is too long is coiled and stored, and one that is too short is replaced, so measure the route before ordering.
Is OM4 worth the cost over OM3 for a 12-fibre trunk?
Where the run is near the OM3 limit, yes. IEEE 802.3 allows 100 m on OM4 for 100GBASE-SR4 against 70 m on OM3. On short runs inside a row the two behave the same, and the choice follows the rest of the plant.
Can I use an MTP-12 OM4 trunk for 10G or 25G duplex links?
Yes, through MPO to LC cassettes or a breakout cable. A 12-fibre trunk gives six duplex channels, and each channel stays within the reach IEEE 802.3 gives for 10GBASE-SR or 25GBASE-SR.