6.4 Coaxial Cable Termination: F-Type, BNC & Compression Connectors
Key Takeaways
- BICSI's own scope statement for Installer 1 names pulling, terminating, and testing copper and coaxial cable, and the exam content outline lists perform coaxial termination as a task in the 15%-weighted Terminate area.
- The standard Series 6 preparation is a two-blade quarter-inch by quarter-inch strip: about 1/4 inch of bare center conductor exposed, and about 1/4 inch of dielectric with the folded braid and foil behind it.
- Compression connectors are the professional standard because the compression sleeve drives a 360-degree seal onto the jacket; twist-on connectors are not acceptable for permanent structured cabling.
- A single stray braid strand touching the center conductor shorts the cable and is the single most common coaxial termination failure, which is why the braid is folded neatly back over the jacket before the connector is seated.
- NEC Article 820 requires the outer conductive shield of a coaxial cable entering a building to be bonded or grounded as close as practicable to the point of entrance.
Coaxial Cable Termination: F-Type, BNC & Compression Connectors
BICSI describes the Installer 1 skill set as including "pulling cable, terminating, and testing copper and coaxial cable," and the published Exam Content Outline lists "perform coaxial termination" as a task inside the 15%-weighted Terminate Copper and Fiber Cable area. Coaxial termination is also a recurring hands-on exam station. Section 2.3 covered coaxial cable construction and impedance; this section covers putting a connector on it correctly.
1. What Makes Coaxial Termination Different
A balanced twisted-pair termination is about preserving pair geometry. A coaxial termination is about preserving concentricity. The cable is a transmission line whose 75-ohm impedance is set by the ratio of the center conductor diameter to the dielectric diameter. Anything that disturbs that geometry at the connector — an off-center pin, a crushed dielectric, a partially seated connector — creates an impedance discontinuity and reflects signal, exactly as described for twisted pair in Section 7.2.
| Cable | Impedance | Center Conductor | Typical Use |
|---|---|---|---|
| Series 6 (RG-6) | 75 ohm | 18 AWG | Broadband CATV, satellite, cable modem, digital video — the premises standard |
| Series 11 (RG-11) | 75 ohm | 14 AWG | Long, low-loss backbone and feeder runs |
| Series 59 (RG-59) | 75 ohm | 20-22 AWG | Legacy analog CCTV baseband video |
Shielding is described by layer count: dual-shield (foil + braid), tri-shield, and quad-shield (foil, braid, foil, braid). Connector bodies are sized for the shield construction — a quad-shield RG-6 connector will not compress correctly onto a dual-shield cable and vice versa. Match the connector to the exact cable series and shield count.
2. Connector Families
+-----------------------------------------------------------------------------+
| COAXIAL CONNECTOR FAMILIES |
| |
| [F-TYPE, COMPRESSION] Threaded 3/8-32 nut. The cable's own center |
| conductor becomes the pin. A compression sleeve is |
| driven home by a compression tool, producing a |
| 360-degree mechanical and moisture seal. |
| >>> THE STRUCTURED CABLING STANDARD <<< |
| |
| [F-TYPE, HEX CRIMP] Older style; a hex die crimps a ferrule. Adequate |
| indoors but far less weather-resistant. |
| |
| [F-TYPE, TWIST-ON] Screws onto the cable by hand. NOT acceptable for |
| permanent installations - poor shield contact, |
| pull-out failures, moisture ingress. |
| |
| [BNC] Bayonet quarter-turn locking. Separate center PIN |
| is crimped onto the center conductor, then the |
| body ferrule is crimped or compressed. CCTV, |
| broadcast video, test equipment. 50 and 75 ohm |
| versions exist - do not mix them. |
+-----------------------------------------------------------------------------+
3. The Quarter-Inch by Quarter-Inch Preparation Standard
A two-blade coaxial stripper produces the industry-standard Series 6 preparation in one rotation.
+-----------------------------------------------------------------------------+
| STANDARD SERIES 6 STRIP GEOMETRY |
| |
| |<-- 1/4 in -->|<-- 1/4 in -->| |
| | (center) | (dielectric)| |
| |
| ===================== |
| ||||| JACKET |||||||===== |
| ===================== DIELECTRIC ===== CENTER CONDUCTOR ------------ |
| ||||| JACKET |||||||===== |
| ===================== |
| ^ |
| | BRAID + FOIL FOLDED BACK over the jacket, smooth and even |
+-----------------------------------------------------------------------------+
Step by Step
- Square-cut the cable with a coax cutter, not side cutters. A crushed oval end will never seat concentrically.
- Set the stripper for the cable series and rotate it two or three turns with light pressure. The outer blade removes jacket, braid, foil, and dielectric to expose about 1/4 in (6 mm) of bare center conductor; the inner blade removes only jacket to expose about 1/4 in of dielectric with the shield behind it.
- Inspect the center conductor. It must be straight, clean, and unnicked. A nicked center conductor snaps in the F-port and a bent one will not enter the connector's pin channel.
- Fold the braid back smoothly and evenly over the outside of the jacket. Do not leave it flared, and do not trim it away — the braid is the return path and the connector clamps onto it.
- Clear every stray strand. Sight down the end and pick or trim any braid whisker that has fallen across the dielectric face.
- Leave the foil in place and tight against the dielectric. The foil, not the braid, is the primary high-frequency shield.
- Push the connector on until the dielectric is flush with the connector's internal collar — look through the connector's inspection window or check that the dielectric reaches the visible shoulder. A connector that is not bottomed out will not compress correctly.
- Compress with the matching compression tool. The sleeve should end flush with the connector body.
- Verify the pin projection. After compression the center conductor should extend just past the connector face — roughly 1/16 to 1/8 in (1.5 to 3 mm). Too short and it will not reach the port contact; too long and it bottoms out and damages the equipment port.
- Torque threaded F connectors to the manufacturer's value with a torque wrench — commonly around 30 in-lb. Hand-tight is loose; pliers-tight crushes the port.
[!CAUTION] The number one coaxial defect is a shorted braid. One stray braid strand bridging the dielectric to the center conductor puts a dead short across the cable. It passes a visual glance, kills the signal completely, and is invisible once the connector is compressed. Sight down every prepared end before the connector goes on.
4. BNC Assembly for CCTV and Video
A BNC connector differs from an F connector in one critical way: the pin is a separate part.
- Strip to the connector manufacturer's dimensions (BNC strip lengths are connector-specific — read the instruction sheet).
- Slide the ferrule onto the cable before anything else. Every installer has crimped a BNC with the ferrule still on the bench.
- Crimp the center pin onto the center conductor with the correct die. Confirm the conductor is visible in the pin's inspection hole and that the pin is fully seated.
- Fold the braid back, insert the assembly into the connector body until the pin clicks home.
- Slide the ferrule forward and crimp with the matched hex die — the wrong die size is the most common BNC failure.
Compression BNC connectors follow the F-type process instead and are preferred where moisture or vibration is a factor.
5. Bonding, Bend Radius, and Verification
- Bonding and grounding: NEC Article 820 governs coaxial distribution. The outer conductive shield of a coaxial cable entering a building must be bonded or grounded as close as practicable to the point of entrance, typically at a listed ground block bonded to the building grounding electrode system. This is the coaxial parallel to the primary protection rules covered in Sections 2.1 and 4.2.
- Bend radius: coaxial cable holds a 10x outer-diameter bend radius (Section 5.2). A kinked coax has a permanently changed impedance at the kink.
- Pulling tension: approximately 35 lbf (155 N) for Series 6 and 50 lbf (222 N) for Series 11, per Section 5.2.
- Verification: check continuity center-to-center and shield-to-shield, then confirm no short between center and shield. Beyond DC checks, coaxial links are verified with a signal level meter for level and tilt, and faults are located with a TDR exactly as described for copper in Section 8.3. On a video system, a picture that is present but soft or ghosted is the classic symptom of an impedance mismatch at a poorly compressed connector.
Using a standard two-blade coaxial stripper on Series 6 cable, what preparation geometry does the tool produce?
A newly compressed F-type connector on a Series 6 drop shows no signal at all, and a meter reads a dead short between the center conductor and the shield. What is the most probable cause?
Under NEC Article 820, what is required of the outer conductive shield of a coaxial cable that enters a building from outside?