NCCER Telecom flashcards

31 cards. Read the term and the definition here. The deck at the top of this page is optional.

Ohm's law

Voltage equals current multiplied by resistance (V = I × R). Used to check conductor loading, calculate voltage drop, and confirm a circuit will operate within equipment ratings.

Power formula

Electrical power equals voltage times current (P = V × I), and also I²R or V²/R. It determines heat load, conductor ampacity needs, and equipment supply sizing.

Decibel definition

A logarithmic ratio comparing two power levels: dB = 10 log(P1/P2). Positive values mean gain, negative values mean loss, and 3 dB equals a doubling of power.

Characteristic impedance

The inherent AC resistance of a transmission line, set by conductor geometry and insulation. Twisted pair is near 100 Ω, video coax 75 Ω, and many RF runs 50 Ω.

Horizontal cabling limit

TIA-568 permits 90 m of permanent horizontal link plus up to 10 m of patch cords, giving a maximum 100 m channel. Exceeding it risks failing insertion loss and length tests.

Single-mode fiber

Fiber with an approximately 8–10 µm core carrying one propagation mode. Used with 1310 nm or 1550 nm sources for long-distance and high-bandwidth links with low attenuation.

Multimode fiber

Fiber with a 50 or 62.5 µm core supporting many light paths, used with 850 nm or 1300 nm sources. Suited to shorter building and campus runs; modal dispersion limits distance.

T568B pinout

Wiring order for an RJ45 jack: white-orange, orange, white-green, blue, white-blue, green, white-brown, brown. Both ends must use the same scheme for a straight-through link.

Telecommunications bonding conductor

The conductor that connects the telecommunications main grounding busbar to the telecommunications grounding busbar and to the building grounding electrode system, per TIA-607 and NEC.

Split pair fault

A wiring error where a conductor from one pair is paired with a conductor from another. Continuity passes but crosstalk rises sharply, causing NEXT failures.

Velocity of propagation

The speed of a signal in a cable expressed as a fraction of the speed of light, typically 0.6–0.8 for copper. Testers use NVP to convert reflection time into length.

NEC Article 800

The National Electrical Code article governing communications circuits, covering cable listing, protection, grounding, and separation from power conductors in buildings.

Insertion loss

Signal power lost as it travels through a link, expressed in decibels at a specified frequency. It rises with length, temperature, and poor connections or terminations.

Near-end crosstalk

NEXT measures signal coupled from one pair into another, measured at the same end as the transmitter. Higher NEXT values in dB mean better separation between pairs.

Return loss

The ratio of reflected signal to incident signal at an impedance mismatch, in dB. Poor terminations, kinks, and wrong connectors degrade return loss and raise bit errors.

Fiber end-face inspection

Examining a connector ferrule under a 200×–400× scope before mating. Scratches, pits, or debris cause high loss and must be cleaned and re-inspected.

OTDR trace

A time-domain reflectometry plot of backscattered light versus distance, showing splice and connector losses and reflective events. Correct index of refraction and pulse width are required.

Optical loss budget

The maximum allowable loss for a fiber link, calculated from source power, receiver sensitivity, connector and splice losses, and fiber attenuation. Measured loss must stay below it.

Reference power measurement

Recording the source output at the meter before testing a link. This reference is subtracted from the measured level to give link loss in dB.

Ground resistance test

Using a ground resistance tester to measure resistance from the telecommunications ground bar to earth. Low resistance confirms a safe fault-current path.

Wire map test

A continuity test verifying each pin connects to the correct pin at the far end. It detects opens, shorts, crossed pairs, and split pairs before other tests run.

Certification tester calibration

Verifying the field tester's calibration status and reference before testing. An out-of-calibration tester invalidates results and can cause false pass or fail reports.

Link length test

A tester measurement of cable length using TDR and the set NVP. Results over the 90 m permanent link limit fail the TIA-568 length requirement.

Attenuation test

A fiber or copper measurement of signal loss through the link at specified wavelengths or frequencies. Results are compared to the calculated loss budget for pass/fail.

Cable labeling

Marking both ends of every cable with the same unique identifier matching the as-built drawings, enabling traceability during moves, adds, and troubleshooting.

Test report traceability

Recording tester serial number, calibration due date, date, operator, and link ID with results so the certification report can be audited and reproduced later.

Patch cord length rule

Total patch cord length in a channel must not exceed 10 m when the permanent link is at its 90 m maximum, keeping the channel within 100 m.

Index of refraction setting

The fiber-specific value entered into an OTDR that converts time to distance. An incorrect value shifts reported event distances and can misplace faults.

Launch and receive cable

Fiber reference cables attached to both OTDR ports to measure the near and far connectors accurately. Without them, end connector loss is hidden in the dead zone.

Continuity verification

Confirming a conductor path is complete and unbroken using a meter or tester before energizing. It is the first check after termination and before certification.

As-built documentation

The final record of installed cable routes, labels, terminations, and test results reflecting actual field conditions. It supports maintenance and future upgrades.