NCCER Telecom common mistakes
NCCER Telecom · Understand the traps and how to avoid them.
Treating the two copper conductors of a twisted pair as interchangeable and landing tip and ring on arbitrary terminals, then testing only for continuity.
Continuity passes even when polarity is reversed, so the error stays hidden until a service turns up with reversed-battery trouble or a phone fails to ring. Candidates study color codes as a memory exercise rather than as a wiring rule.
What to do instead
Practice terminating 25-pair and 4-pair cables until tip and ring positions are automatic, then verify with a polarity/voltage test rather than a continuity test. Be able to state the standard color sequence (white-blue through violet-slate) and the pair-group binder colors without looking them up.
Applying the wrong bend radius or pulling tension to fiber and copper cable, or ignoring it entirely during a hands-on cable-pull station.
Candidates memorize the idea that fiber is fragile but not the numbers or the reason behind them; under time pressure in a performance station they pull hard to finish quickly and induce micro-bend loss or a broken strand that only shows on an OTDR trace.
What to do instead
Learn the rule of thumb for outside-plant and inside-plant cable (roughly 10x and 20x the cable diameter for installed and pulled conditions) and the manufacturer tension limit, and rehearse a pull while narrating the limit you are respecting. Treat any kink or cinched tie as a fail and re-terminate.
Reading a power meter or OTDR result without zeroing the meter, cleaning and inspecting the connectors, or setting the correct reference/wavelength first.
Dirty end faces and an unzeroed meter both produce plausible-looking loss numbers, so the candidate reports a passing link or chases a phantom fault. The procedural steps feel like formalities and get skipped.
What to do instead
Follow a fixed sequence every time: inspect with a scope, clean both end faces, attach reference cords, zero/set the reference, then measure at the specified wavelength in both directions. Record the reference value and the measurement so the tester can see the procedure was done.
Confusing the roles of the NEC, TIA/EIA cabling standards, and OSHA in a knowledge question, answering with whichever document sounds most authoritative.
All three govern the same job site, and candidates who learned them as a blur of acronyms cannot separate electrical safety, cabling performance, and worker safety. Distractors exploit exactly this overlap.
What to do instead
Build a one-page map: NEC (NFPA 70) covers electrical installation and safety requirements; TIA/EIA-568 and related standards cover cabling topology, distances, and performance; OSHA covers workplace safety and training. Tie each to a concrete example such as conduit fill, horizontal run length, and fall protection.
Skipping or rushing lockout/tagout and voltage verification before working on telecom circuits, assuming low-voltage means safe.
Telecom circuits routinely carry battery voltage and can be exposed to power-cross or lightning-induced surges; candidates equate 'low voltage' with 'no hazard' and treat the performance-station safety steps as a formality.
What to do instead
Demonstrate the full sequence: identify and notify, isolate, lock and tag, verify absence of voltage with a tested meter, then work. Be able to explain power-cross and why a fused protector or a grounded protector block matters, and state the shock hazard of -48 V DC battery strings.
Mixing up decibel arithmetic, especially treating dB and dBm as interchangeable, or adding losses incorrectly when computing a link budget.
Both use the same logarithmic scale, and candidates memorize formulas without understanding that dBm is an absolute power referenced to 1 mW while dB is a relative ratio. Losses add in dB, but powers do not add linearly.
What to do instead
Work through link budgets by hand: start with transmitter output in dBm, subtract each loss in dB, add each gain in dB, and compare to receiver sensitivity in dBm. Practice converting a few values (3 dB = 2x, 10 dB = 10x, 0 dBm = 1 mW) until the distinction is automatic.
Terminating a connector or splice without following the specified strip length and cleave angle, then assuming a bad reading means faulty test equipment.
Fiber cleave quality and strip length are invisible once the connector is assembled, and candidates under time pressure rush the cleave or leave a bubble in the splice. When loss is high they blame the OTDR instead of their own workmanship.
What to do instead
Rehearse the cleave-and-inspect step separately, checking the end face before splicing or connectorizing, and use a visual fault locator or OTDR to confirm the result. Know typical acceptance values (for example, a fusion splice well under 0.1 dB and a field connector under 0.3 dB) and redo rather than rationalize a bad number.
Grounding and bonding the telecom system to whatever metal is nearby, or omitting the telecommunications bonding conductor back to the service ground.
Grounding looks like a single wire, so candidates connect to a convenient conduit or water pipe without understanding that a separate, unbonded ground path creates a difference in potential and a lightning/surge hazard. Knowledge questions on the grounding electrode system expose this gap.
What to do instead
Learn the required single-point bonding path: telecommunications ground bar bonded to the building's grounding electrode system with the specified conductor, plus bonding of cable shields and protectors. Be able to explain why multiple independent grounds are dangerous and identify the correct bonding point in a described installation.
Testing only one direction or one wavelength on a fiber link, or documenting results without recording test conditions, so the performance verification is incomplete.
Bidirectional and dual-wavelength testing is tedious, and candidates assume a link that passes at 1310 nm will pass at 1550 nm. Incomplete records also fail the documentation portion of a performance check.
What to do instead
Adopt a checklist: both directions, all specified wavelengths, launch conditions matched to the method, and a record of meter model, reference values, date, and technician. Treat an incomplete test set as a failed test and be able to say why macrobend loss appears at 1550 nm but not at 1310 nm.
Answering code and standard questions from memory of how the crew does it on site rather than from the actual requirement, and not flagging when a question turns on a specific distance or value.
Field habits vary and often reflect older practice; candidates generalize from one job and pick the familiar-sounding distractor. Questions that hinge on a number (run length, fill percentage, clearance) punish guessing.
What to do instead
Study the numeric limits as a short reference list (horizontal cabling distance, conduit fill, separation from power, bend radius) and, during the exam, identify which specific value the question is testing before choosing. Where a value is uncertain, reason from the underlying principle rather than the site habit.