An SC connector is a fibre optic connector with a 2.5 mm ceramic ferrule and a square push-pull body that snaps into its adaptor, defined in IEC 61754-4. It is made in simplex and duplex form, with UPC polish (blue) or 8 degree APC polish (green). SC/APC is the usual connector in FTTH and passive optical networks.
What an SC connector is
The SC connector was developed by NTT in Japan in the 1980s, and its interface is standardised in IEC 61754-4. It holds the fibre in a 2.5 mm zirconia ferrule, the same diameter used by FC and ST, inside a square moulded body. It was one of the first connectors designed to latch with a straight push instead of a twist or a thread, which made it a common choice in telecom and enterprise networks before the smaller LC arrived.
An SC plug has an inner housing that carries the spring-loaded ferrule, and an outer sliding grip. When the plug is pushed into the adaptor, latches inside the adaptor catch the inner housing. Pulling the outer grip slides it back over those latches and releases them. A pull on the cable alone does not unlatch the plug, which suits frames where cords are routed under tension.
A key on one face of the body fixes orientation in the adaptor. On flat UPC connectors that only keeps cords tidy, but on angled APC connectors the key holds the 8 degree faces in the correct alignment.
Simplex and duplex SC
A simplex SC carries one fibre. A duplex SC joins two simplex plugs with a clip at a 12.7 mm centre-to-centre pitch, the spacing used by SC duplex adaptors and by older duplex optics such as GBIC transceivers and many media converters. Duplex clips usually mark the two positions A and B, and as with any duplex cord the standard patch cord is an A-B crossover, so transmit at one end reaches receive at the other.
SC cords are commonly built on 2.0 mm or 3.0 mm round cable, and SC pigtails on 0.9 mm buffered fibre for splicing inside a tray. SC is also a common format for field-installable connectors on FTTH drop cables, where a technician fits the plug on site instead of splicing a pigtail.
Simplex SC adaptors come in flanged and snap-in styles, and duplex adaptors join two ports in one body. One SC simplex cut-out in a panel takes a duplex LC adaptor, which is how many frames have been converted to higher density without replacing the panel.
SC/UPC vs SC/APC
On single-mode fibre the SC comes in two polish types, and the colour convention is consistent enough to rely on in the field. Multimode SC connectors are PC or UPC.
| Version | End face | Body colour | Return loss (typical industry values) | Typical use |
|---|---|---|---|---|
| SC/UPC single-mode | Domed, flat contact | Blue | 50 dB or better | Ethernet optics, telecom transport, older enterprise links |
| SC/APC single-mode | Domed, 8 degree angle | Green | 60 dB or better | FTTH and PON, RF video overlay, CATV |
| SC multimode | PC or UPC | Beige (OM1, OM2) or aqua (OM3, OM4) | Lower; rarely the limiting figure | Older campus, building and industrial links |
The 8 degree angle on an APC end face sends reflected light into the cladding, where it is lost, instead of back along the core towards the laser. Our guide to UPC vs APC polish covers the geometry. Never mate SC/APC with SC/UPC: the angled and flat faces leave an air gap, the loss is high and both end faces can be damaged. Adaptors follow the same colour code, so a green adaptor should only take green plugs.
Insertion loss for a mated single-mode SC pair with clean end faces is commonly 0.3 dB or less (a typical industry value). ANSI/TIA-568 allows up to 0.75 dB per mated pair in a channel loss budget. State the maximum you need per mated pair in the order.
Why FTTH, PON and video overlay use SC/APC
Passive optical networks such as GPON and XGS-PON carry downstream and upstream traffic on different wavelengths over one fibre, through passive splitters that serve many homes. Many operators also run an RF video overlay at 1550 nm to carry television channels. Analogue RF signals are sensitive to reflections: light bouncing back from a connector joint interferes with the signal and appears as noise and distortion. The higher return loss of an APC end face keeps those reflections down.
A PON path from the exchange to the home also passes through many joints: the OLT patch, the ODF, splitter modules, street cabinets, a distribution point and the terminal in the home. Each one adds a little reflection, so a polish that suppresses it gives margin across the whole path. The SC body is large enough to handle with gloves in a cabinet or on a pole, and SC/APC is the usual format on PLC splitter modules, fibre terminal boxes and many ONT ports.
Not every port in a PON is APC. Some OLT optics have SC/UPC receptacles, so check each port before ordering, and use a cord with APC on one end and UPC on the other only where the two ends genuinely differ.
Where SC connectors are used
- Optical distribution frames and patch panels in exchanges and central offices, where SC/UPC and SC/APC have long been standard.
- Splitters and FTTx: PLC splitter modules, distribution and terminal boxes, drop cables and ONTs.
- CATV and RF over fibre: transmitters, receivers and nodes that need low reflection, usually SC/APC.
- Older enterprise and telecom kit: GBIC transceivers, media converters, SDH and SONET line cards, and building backbone panels installed before LC became common.
- Test equipment: power meters, light sources and OTDRs often take interchangeable port adaptors, and SC is a common fitted option.
For new data centre and switch work, duplex LC has largely replaced SC because of density. The SC fiber connector remains the normal choice where the frame, the splitter or the operator's standard already uses it.
SC vs LC
| Feature | SC | LC |
|---|---|---|
| Ferrule | 2.5 mm | 1.25 mm |
| Interface standard | IEC 61754-4 | IEC 61754-20 |
| Release | Pull the outer grip | Press the latch arm |
| Duplex pitch | 12.7 mm | 6.25 mm |
| Panel density | Lower | About twice SC in the same space |
| Common polish | UPC and APC both common | Mostly UPC, APC available |
| Typical home | FTTH and PON, ODFs, older enterprise kit | Transceivers, data centre panels, cassettes |
| Handling | Larger; easy with gloves | Small; a pull tab helps in tight panels |
Loss performance is similar when both are well made. Choose SC where the equipment or installed frame already uses it, or where technicians work with gloves. Choose LC where port density matters. Our LC connector guide covers duplex LC polarity and uniboot cords.
Adaptors and SC to LC hybrid cords
SC and LC do not mate directly because their ferrules differ in diameter. There are two ways to join them:
- Hybrid patch cord: SC on one end and LC on the other, simplex or duplex. This is the preferred method because it adds no extra joint. See our LC to SC patch cords.
- Hybrid adaptor: an SC receptacle on one side and an LC receptacle on the other, with a sleeve bored to a different size at each end. It adds a joint and can be less stable over repeated mating, so keep it for testing or temporary work.
For SC to SC links, a standard adaptor joins two plugs. Single-mode adaptors should use a zirconia split sleeve for alignment; phosphor bronze sleeves are found on some multimode adaptors. Match the adaptor to the plugs: green for APC, blue for single-mode UPC.
What to specify when ordering SC cords
- Connector at each end: SC to SC, or SC to LC, FC or ST.
- Polish at each end: UPC or APC, including mixed APC to UPC cords where a port requires it.
- Fibre type: OS2 single-mode, or the multimode grade of the installed plant.
- Simplex or duplex, and for duplex, A-B polarity unless the channel design calls for A-A.
- Length and tolerance, measured connector tip to connector tip.
- Cable diameter and jacket: 0.9 mm, 2.0 mm or 3.0 mm, LSZH, or a riser or plenum rating where the local code calls for one.
- Loss limits and test records: maximum insertion loss per mated pair, minimum return loss, and whether a test sheet should ship with each cord.
- Labelling: jacket legend and ID labels at each end.
Radix builds SC to SC patch cords and SC assemblies to order in Pune. Send the details above, with quantities, through the quote request form.
Questions buyers ask
What is the difference between SC/UPC and SC/APC?
SC/UPC has a domed end face that meets its partner square on and is coloured blue. SC/APC is polished at 8 degrees and coloured green, which sends reflected light out of the core and gives higher return loss. The two must not be mated together.
Why are SC/APC connectors used in FTTH?
FTTH and PON links pass through many connectors and splitters, and many carry an RF video overlay at 1550 nm that is sensitive to reflections. The angled APC end face keeps back reflection low. The SC body is also easy to handle in cabinets and terminal boxes.
What does SC stand for?
Accounts differ. It is often called subscriber connector, square connector or standard connector, and it was developed by NTT. In practice the name identifies the push-pull connector with a 2.5 mm ferrule defined in IEC 61754-4.
Can I connect an SC connector to an LC port?
Not directly, because the ferrules are 2.5 mm and 1.25 mm. Use a hybrid patch cord with SC on one end and LC on the other. Hybrid adaptors exist, but they add a joint and are best kept for testing.
Is the SC connector single-mode or multimode?
It is made for both. Single-mode SC comes in blue UPC or green APC; multimode SC is usually beige for OM1 and OM2 or aqua for OM3 and OM4. Match the connector to the fibre type and to the port it plugs into.