LC vs SC Fiber Connectors: Differences, Uses and Duplex Polarity
LC and SC are the two most common single-fiber connectors. SC has a 2.5 mm ferrule in a square push-pull body; LC has a 1.25 mm ferrule with a latch and takes about half the space. Loss performance is similar. Choose LC for switches, SFP optics and dense panels, and SC where equipment, such as FTTH ONTs, has SC ports.
Every link that is not MPO ends in a single-fiber connector, and in data centers, enterprise networks and access networks that connector is almost always LC or SC. Both use a precision ceramic ferrule and physical-contact polish, so the choice is rarely about optical quality. It comes down to which port the equipment has, how much panel space you have, and how the duplex pair is wired. This guide compares the two, explains colours and polish, and shows how A-B duplex polarity keeps transmit going to receive.
LC vs SC at a Glance
| LC | SC | |
|---|---|---|
| Ferrule diameter | 1.25 mm | 2.5 mm |
| Form factor | Small form factor (SFF) | Standard size, square body |
| Coupling | Latch (tab, like a small phone plug) | Snap-in push-pull |
| Intermateability standard | FOCIS-10 (TIA-604-10) | FOCIS-3 (TIA-604-3) |
| Duplex version | Yes, with a clip | Yes, with a clip |
| Typical ports | SFP/SFP+/SFP28 and QSFP duplex optics, switches, high-density panels | FTTH ONTs and splitters, older patch panels, some telecom equipment |
| Polish options | UPC or APC (single-mode), PC/UPC (multimode) | UPC or APC (single-mode), PC/UPC (multimode) |
| Panel density | About twice SC | Baseline |
Both connectors are covered by the TIA FOCIS intermateability standards, which is why an LC or SC from any compliant maker fits a standard adapter of the same type.
The SC Connector
The SC is a snap-in connector with a 2.5 mm ceramic ferrule. It latches with a simple push-pull motion and comes in simplex and duplex versions. It was the connector standardized in TIA-568-A, but at first it cost more than the ST and spread slowly. Today it is common and inexpensive.
The SC is easy to handle and hard to damage: the square body protects the ferrule, and the push-pull latch needs no twisting. That makes it a good fit for places where connections are made by hand, in the field or by users. The 2.5 mm ferrule is shared with ST and FC connectors, so a hybrid adapter can mate SC to ST or FC, which is useful for test equipment.
In access networks, SC/APC (green) is the usual connector at FTTH ONTs, splitters and terminals. Many operators specify an SC/APC patch cord to the ONT, because PON links are sensitive to reflections.
The LC Connector
The LC is a small form factor connector with a 1.25 mm ferrule, half the size of the SC ferrule. Otherwise it is a standard ceramic-ferrule connector, terminated and polished the same way. A latch tab holds it in the adapter, and a duplex clip joins two LCs into a pair.
Of the small form factor designs introduced in the late 1990s, LC is the one that won. It is now the standard duplex interface on pluggable optics: SFP, SFP+ and SFP28 transceivers use a duplex LC receptacle, and so do duplex QSFP optics such as 100G and 400G FR/LR types. In patch panels, LC fits about twice as many fibers into the same space as SC, and LC is the usual front interface of MPO-to-LC cassettes and breakout harnesses.
Size and Density
The smaller ferrule makes the whole connector smaller. A duplex LC occupies roughly the footprint of one simplex SC, so a 1U panel or a switch faceplate holds about twice as many LC ports. In a data center that difference adds up quickly, which is why new high-density cabling uses LC at the edge and MPO in the backbone.
SC's larger body is easier to grip with gloves and easier to label. Where port density does not matter, as in an ONT or a wall outlet, SC remains a practical choice.
Newer very small form factor connectors, such as CS, SN and MDC, also use 1.25 mm ferrules and pack even more fibers into the same space. They suit specific high-density optics; for most links, LC and SC remain the default.
Colours and Polish
The connector body and boot colour show the fiber type and polish. TIA-568 sets beige for multimode, blue for single-mode UPC and green for single-mode APC. Many makers use aqua for OM3 and OM4 multimode and lime for OM5, matching the cable jacket.
| Colour | Meaning |
|---|---|
| Blue | Single-mode, UPC polish |
| Green | Single-mode, APC 8° polish |
| Beige | Multimode (TIA-568 convention) |
| Aqua | Multimode OM3 or OM4 (common practice) |
| Lime | Multimode OM5 (common practice) |
Polish is independent of the connector type: there are LC/UPC, LC/APC, SC/UPC and SC/APC versions. The rule from our APC vs UPC guide applies here too: never mate APC with UPC. The 8° and flat end faces leave an air gap, which causes high loss, poor return loss and can damage the end faces. Colour is a quick check, but the printed legend and the order specification are the real proof.
Huawellux LC and SC patch cords are specified at insertion loss ≤0.35 dB, with return loss ≥50 dB for single-mode UPC, ≥60 dB for single-mode APC (OS2) and >30 dB for multimode (OM4/OM5).
Where Each Connector Is Used
Choose LC when: - The port is an SFP, SFP+, SFP28 or duplex QSFP transceiver. - You need high density in patch panels, cassettes or switch faceplates. - You are building data center or enterprise backbone links that break out from MPO trunks.
Choose SC when: - The equipment has SC ports, such as FTTH ONTs, PON splitters or older patch panels. - Connections are made in the field or by end users, where a larger, robust connector helps. - An existing installation is already standardized on SC.
Mixed links are normal. A data center switch with LC optics may connect to a building or carrier panel with SC adapters. In that case use an LC-to-SC patch cord, not an adapter. The ferrules differ in size, so LC and SC cannot be mated directly through a simple adapter.
Duplex Polarity: A-to-B Cords
Most LC and SC links are duplex: one fiber transmits (Tx) and one receives (Rx). Polarity means that the transmitter at one end always reaches the receiver at the other. TIA defines two types of duplex patch cord:
- A-to-B: position A at one end connects to position B at the other end. This is the type TIA recommends for duplex patch cords.
- A-to-A: position A connects to position A. It is used only where a specific polarity method needs it, such as one end of an MPO Method A channel.
In TIA terminology, B is the transmit position and A is receive. Facing an open duplex port with the key up, B is on the left and A on the right. In a channel made of A-B components at every stage, the signal leaves Tx (B), arrives at Rx (A) at the far end, and polarity holds, however many segments there are.
A note on names. Some manufacturers call an A-B cord "straight-through" and A-A "crossover", while others use the same words the other way round. To avoid confusion, specify the mapping (A-to-B or A-to-A), not the label.
Fixing a reversed duplex link. If a link shows no light on one side, the pair may be reversed. Many duplex LC clips allow the two connectors to be swapped in the field. Note the change on the label so the documentation stays correct. For MPO channels, the duplex A-B flip is handled by the polarity method; see our MPO polarity guide.
LC to SC, Hybrid and Breakout Cords
Because LC and SC are mixed so often, a few cord types cover most situations:
- LC-LC duplex: switch to switch, or switch to an LC panel or cassette.
- LC-SC duplex: LC optics to an SC panel or SC equipment.
- SC-SC duplex: SC panel to SC equipment.
- Simplex cords: single-fiber links, such as BiDi optics or PON drops.
- Hybrid polish cords (for example LC/UPC to SC/APC): where the two pieces of equipment use different polishes, such as a UPC optic and an APC distribution panel.
- MPO-to-LC harnesses: break a trunk out directly into duplex LCs at the equipment; see our trunk vs patch cable guide.
How to Specify an LC or SC Patch Cord
- Connector at each end: LC or SC (and simplex or duplex).
- Polish at each end: UPC or APC (single-mode); multimode is PC/UPC.
- Fiber type: OS2, OM4 or OM5; see our fiber type guide.
- Polarity: A-to-B (standard) or A-to-A.
- Length, with a little slack for routing.
- Jacket: diameter (for example 2.0 mm or 3.0 mm), colour and fire rating.
- Labeling and test report requirements.
Every Huawellux product receives end-face visual inspection under a 400x video microscope and is tested for insertion loss (IL) and return loss (RL) before it ships. Interferometric end-face geometry (fiber height, coplanarity, end-face angle and radius) is checked by sample-based testing in standard production, and 100% interferometer testing of a batch is available on request. A formal test report is provided on request; state it in your RFQ.
Frequently Asked Questions
What is the difference between LC and SC connectors?
SC uses a 2.5 mm ferrule in a square push-pull body. LC uses a 1.25 mm ferrule with a latch and is about half the size, so it allows roughly twice the port density. Optical performance is similar; the choice depends on the equipment ports and the space available.
Which is better, LC or SC?
Neither is better in general. LC is the standard for SFP and duplex QSFP optics and high-density panels. SC is common at FTTH ONTs, splitters and older panels. Use the connector that matches the ports at each end, with an LC-SC cord where they differ.
Can I connect an LC connector to an SC connector?
Not through a simple adapter, because the ferrules are different sizes. Use an LC-to-SC patch cord, with the correct polish (UPC or APC) at each end.
What is A-B polarity in a duplex patch cord?
In an A-to-B duplex cord, position A at one end connects to position B at the other. With B as transmit and A as receive, the transmitter at one device reaches the receiver at the other. TIA recommends A-B cords for duplex links.
Do LC and SC connectors have different colours?
The colour shows fiber type and polish, not connector type. Blue is single-mode UPC, green is single-mode APC, and multimode is beige, or commonly aqua for OM3/OM4 and lime for OM5. Never mate a green APC connector with a blue UPC connector.
Get LC and SC Patch Cords Built to Your Link
Huawellux manufactures LC-LC, LC-SC and SC-SC patch cords at our factory in Shenzhen, simplex and duplex, in OS2, OM4 and OM5, with UPC or APC polish, A-B or A-A polarity, and hybrid LC/SC APC-to-UPC cords where two pieces of equipment differ. Browse our standard fiber patch cords. For MPO backbones, see our MTP/MPO trunk cables, breakout harness cables and MPO patch cables, built with genuine US Conec MTP® or standard MPO connectors.
Dust caps are fitted on every connector, and a formal test report is available on request.
Huawellux replies to inquiries within 24 hours. Custom orders typically take 1–5 business days to complete production, with final timing confirmed case by case in the quotation. For special/custom requirements, MOQ is 2 km of fiber length. Standard listed patch cords have no formal MOQ. The sample fee is credited against the bulk order.
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