Connectors

Part of Networking

Physical connectors that terminate network cables and join network segments.

Why This Matters

A network cable without proper connectors is useless. The connector is the physical interface between the cable and the network device — it must make reliable electrical contact, maintain correct impedance, and survive repeated connection and disconnection cycles. Poor connectors cause intermittent failures that are among the most difficult network problems to diagnose, because the fault appears and disappears seemingly at random as the connector flexes.

Understanding connectors means understanding both the standardized types you will encounter and the physical principles that make connectors work. Even in a civilization-rebuilding context where manufacturing precision connectors may be impossible, knowing what a good connector looks like helps you evaluate what you can actually use versus what will cause problems. Improvised connections can work, but only when built with an understanding of what the design accomplishes.

The connector must accomplish several things simultaneously: it must make low-resistance electrical contact at each conductor, it must maintain consistent spacing between conductors to preserve impedance, it must shield against electromagnetic interference where shielding is required, and it must mechanically secure the cable to prevent strain on the electrical contacts. Each of these requirements influences the connector’s physical design.

RJ-45 Connectors for Ethernet

The RJ-45 (Registered Jack 45) connector is the standard for Ethernet twisted-pair cabling. It is an 8-position, 8-contact (8P8C) modular connector that accepts cables containing four twisted pairs. The connector is transparent plastic with eight metal contacts on the top that pierce the cable insulation when crimped.

To install an RJ-45 connector, you need the cable, the connector, and a crimping tool. The crimping tool simultaneously pushes the eight contacts through the cable insulation to make electrical contact and deforms a strain relief section to grip the cable jacket. The process requires precise alignment of the eight conductors in the correct order (following either T568A or T568B wiring standards) before inserting them into the connector.

The wiring order matters because the two Ethernet standards (T568A and T568B) place conductors differently. T568B is more common in commercial installations. The order from pin 1 to pin 8 in T568B is: orange-white, orange, green-white, blue, blue-white, green, brown-white, brown. The twist pairs must be untwisted only as far as necessary to seat in the connector — excessive untwisting degrades signal quality.

A common failure mode is incomplete insertion of conductors before crimping. Each conductor must reach the end of the connector and be visible through the transparent plastic before crimping. Any conductor that stops short will not contact its corresponding pin, creating an open circuit on that pair. Testing with a cable tester immediately after crimping catches this error before the cable is routed and the problem becomes difficult to locate.

BNC Connectors for Coaxial Cable

BNC (Bayonet Neill-Concelman) connectors are used with coaxial cable and were standard in older 10Base2 Ethernet networks. The connector has a center pin that contacts the cable’s center conductor and a barrel that contacts the shield, with a quarter-turn bayonet locking mechanism.

Installing a BNC connector on coaxial cable requires stripping the cable in stages: the outer jacket is removed, the braided shield is folded back, the dielectric insulation around the center conductor is removed, and the center conductor is exposed. The center pin is soldered or crimped to the center conductor, the pin is inserted into the connector body, and the barrel is crimped over the folded-back shield.

The critical dimension is the distance between the center conductor and the shield — this dimension, determined by the dielectric material, sets the cable’s characteristic impedance (typically 50 ohms for Ethernet coax). The connector must maintain this impedance at the termination point; a poorly installed connector creates an impedance discontinuity that reflects signal energy back toward the source and degrades performance.

BNC T-connectors join two cable segments and a network device at a single point. The coaxial bus topology that used BNC connectors required a terminator (a resistor matching the cable’s 50-ohm impedance) at each end of the bus. Missing or incorrect terminators caused reflections that disrupted the entire network — a significant reliability problem that eventually drove the adoption of star topologies using RJ-45 connectors instead.

Fiber Optic Connectors

Fiber optic connectors terminate optical fiber cables and align the fiber core with extreme precision so light can pass from one fiber to another with minimal loss. Common connector types include SC (square, push-pull), LC (small form-factor, latch), and ST (bayonet twist-lock).

The critical dimension in a fiber connector is the alignment of the fiber core, which in single-mode fiber is only 8-10 micrometers in diameter. Misalignment of even a few micrometers causes significant insertion loss. This precision makes fiber connectors more difficult to install in the field than copper connectors — most field installations use either pre-terminated cables or mechanical splice connectors that are designed for field use without specialized equipment.

Contamination is the leading cause of fiber connector problems. Dust particles on the fiber end face cause significant optical loss. Fiber connectors must be cleaned before every connection using appropriate cleaning tools. Never touch the fiber end face with fingers. Inspect end faces with a fiber inspection scope (or a simple magnifying lens) before connecting — a contaminated connector can permanently damage a clean connector it mates with.

Improvised and Substitute Connectors

In a low-resource environment, manufactured connectors may not be available. Understanding what connectors must accomplish allows evaluation of alternatives.

For short-distance, low-frequency connections, any reliable electrical contact may be adequate. Stripped wire twisted together and taped provides electrical continuity but no impedance control, no strain relief, and no protection from moisture or mechanical stress. This works for temporary connections in protected environments but fails in real-world use.

Screw terminals and terminal blocks provide better reliability than twisted connections. They clamp conductors mechanically rather than relying on connection tension. For DC control signals or low-frequency analog connections, screw terminals are entirely adequate. For high-frequency digital signals (Ethernet operates at hundreds of MHz), impedance control matters more and screw terminals become problematic.

The practical rule is: for connections that will remain undisturbed in a protected location carrying low-frequency signals, improvised connections can work. For connections that will be made and broken repeatedly, exposed to physical stress or environmental conditions, or carrying high-frequency signals, proper connectors are necessary for reliable operation.

Connector Maintenance and Troubleshooting

Network connectors fail gradually rather than all at once. A connector that worked yesterday may work intermittently today and fail tomorrow. The failure mode is usually increasing contact resistance due to oxidation, contamination, or mechanical wear.

Inspect connectors regularly in high-use or harsh environments. Look for bent or corroded contacts, cracked plastic housings, and cable jackets that have pulled back from the connector (indicating strain relief failure). A cable tester can identify which pairs have problems but cannot always distinguish between a bad connector and a bad cable — if the tester shows a fault, the connector is the first thing to replace or re-terminate.

When diagnosing intermittent network failures, physical connectors should be among the first things checked. Flex the cable at each connector end while watching for network activity to drop — a fault that appears only under physical stress is almost certainly a connector or cable problem. Re-terminating the connector (cutting off the old one and installing a new one) is faster and more reliable than attempting to repair a damaged connector.