Optical Fiber Cables practice questions

Correct: C — To the intersystem bonding termination

Per 770.100(B)(1), when an intersystem bonding termination exists, the bonding conductor must connect there. The grounding electrode system, service raceway, and dedicated rod are all 770.100(B)(2)/(B)(3) fallback options used only when no intersystem bonding termination is present.

Correct: A — 15 m (50 ft)

Under 770.48(A), an unlisted outside-plant fiber cable may run up to 15 m (50 ft) from its point of entrance before it must terminate in an enclosure. The no-limit option confuses this with 770.48(B)'s raceway permission, and the riser-termination option is wrong because 770.48(A) specifically excludes risers from this installation method.

Correct: C — 10 AWG copper

770.100(A)(3) requires the bonding/grounding conductor to be not smaller than 14 AWG and never required larger than 6 AWG, so 10 AWG copper fits within that window. The 16 AWG option is smaller than the 14 AWG minimum, and while 4 AWG isn't prohibited outright, it's outside the typically expected sizing since the rule caps the requirement at 6 AWG (making anything larger unnecessary to specify as the 'required' answer here). 770.100(A)(2) also limits material to copper or other corrosion-resistant conductive material, which rules out aluminum-only options in this context.

Correct: C — 300 mm (12 in.)

770.44(A)(4) requires a minimum of 300 mm (12 in.) separation in the span, including at the building attachment point. The 1.0 m (40 in.) figure is the separate, larger clearance required at the pole, not in the span.

Correct: B — They must be listed as having low smoke and heat release properties

770.24(A) requires plenum cable ties and other nonmetallic cable accessories used to secure and support optical fiber cable in plenums to be listed for low smoke and heat release properties. There is no metallic requirement, no wet-location requirement, and no specific spacing dimension given in this section.

Correct: A — Power-limited fire alarm circuits per Parts I and III of Article 760

770.133(C)(2) permits power-limited fire alarm systems complying with Parts I and III of Article 760. Class 1 circuits and non-power-limited fire alarm circuits are not on the compatible list, and general branch-circuit (Article 210) power conductors are excluded entirely — this section only addresses limited-power/communications-type circuits.

Correct: A — OFNG

Per 770.179(C), OFNG (and OFCG) are resistant to the spread of fire in cable trays per the vertical-tray flame tests. OFN and OFC, per 770.179(D), are general-purpose but not tested or suitable for cable trays. Plenum cable is a separate, higher-rated class not addressed by these sections.

Correct: C — A fireproof riser shaft with firestops at each floor

Per 770.113(F), plenum, riser, and general-purpose cable routing assemblies are permitted in fireproof riser shafts firestopped at each floor. 770.113(E) covers metal raceways but only recognizes cable and communications innerduct there, not routing assemblies. Firestopping at each floor is required either way per 770.26.

Correct: D — 770.133(A)

770.133(A) specifically governs optical fiber cables sharing a cable tray or raceway with electric light, power, Class 1, non-power-limited fire alarm, or medium-power network-powered broadband circuits, and states nonconductive cables are permitted without a barrier while unarmored conductive cables are not. 770.133(B) covers cabinets and outlet boxes, not cable trays, and 770.113(H) only lists what cable types are permitted in cable trays generally, not the co-occupancy rule with power conductors.

Correct: B — 60°C (140°F)

770.179 sets 60°C (140°F) as the minimum temperature rating for all optical fiber cables. The other values are common conductor/equipment temperature ratings elsewhere in the NEC, but they are not the floor set for optical fiber cable in this section.

Correct: A — Bare Types OFNP, OFCP, OFNR, OFCR, OFNG, OFCG, OFN, or OFC are permitted directly in the tray

770.113(H)(1) permits Types OFNP, OFCP, OFNR, OFCR, OFNG, OFCG, OFN, and OFC to be supported by cable trays with no raceway required; a raceway is only an additional option under (H)(2), not a mandate.

Correct: C — Ground or bond the metallic member per 770.100, or interrupt it with an insulating joint, as close as practicable to the point of entrance

770.93(A) requires the non-current-carrying metallic member to be grounded or bonded per 770.100, or interrupted with an insulating joint or equivalent device, located as close as practicable to the point of entrance. There is no conduit substitute, no exemption for a continuous run, and no length-based threshold in the section.

Correct: C — A bonding jumper not smaller than 6 AWG copper or equivalent between the two electrodes

770.100(D) requires a bonding jumper of at least 6 AWG copper or equivalent between the grounding electrode and the power grounding electrode system when separate electrodes are used. The no-connection option ignores the potential-difference hazard the rule exists to prevent, the 8 AWG option understates the minimum size, and reusing the power electrode isn't what the rule requires — separate electrodes are permitted as long as they're bonded.

Correct: B — 12 AWG

770.106(B) sets the minimum at 12 AWG copper or an equivalent corrosion-resistant material. The 8 AWG, 10 AWG, and 6 AWG options are all larger than what the rule actually requires as a minimum.

Correct: B — They must be grounded in accordance with 770.100(B)(3)

Per 770.106(A)(1), when no mobile home service equipment is within 30 ft (9.0 m) of the exterior wall, the metallic members must still be grounded per 770.100(B)(3). The 'no current, no grounding needed' distractor confuses current-carrying conductors with metallic strength/armor members, which need grounding regardless of current.

Correct: A — 770.25

770.25 requires the accessible portion of abandoned optical fiber cables to be removed unless tagged for future use. 770.24 covers mechanical execution of work (installation practices, not abandonment), and 770.26 covers spread of fire/products of combustion, not removal requirements — neither addresses abandoned cable disposition.

Correct: C — Slack and bundled cable must not accumulate enough to prevent lifting the tile to reach the box.

770.21 bars fiber cable accumulation from blocking removal of panels that provide access to electrical equipment, and it names suspended ceiling panels specifically as covered. Being non-conductive doesn't exempt fiber cable, and the equipment behind the panel isn't limited to communications gear.

Correct: B — Connect it to a grounding electrode or the building grounding electrode system with a bonding or grounding electrode conductor

770.49 requires metal conduit containing optical fiber entrance cable to be connected by a bonding conductor or grounding electrode conductor to a grounding electrode, or the building grounding electrode system if present, per 770.100(B). This applies regardless of whether the fiber carries current or shares a path with power conductors; the concern is the metal raceway itself, not the cable inside it.

Correct: A — The opening must be firestopped using an approved method to maintain the fire resistance rating

770.26 requires that openings around penetrations of optical fiber cables and communications raceways through fire-resistance-rated assemblies be firestopped with approved methods. A riser listing addresses flame/smoke spread along the cable itself, not the fire rating of the penetrated assembly, so it doesn't substitute for firestopping. The requirement applies regardless of occupancy, and swapping cable types doesn't remove the need to firestop the opening.

Correct: A — As an electrical cable, in accordance with the type of electrical conductors it contains

770.3(C) states hybrid optical fiber cables are classified as electrical cables according to the type of electrical conductors they contain — the fiber content doesn't set the classification, and there's no blanket exemption or default communications classification.

Correct: D — 770.44(B)

770.44(B) sets the 2.5 m (8 ft) vertical clearance for optical fiber cables passing above roofs, with the reduced-clearance exceptions for overhangs and sloped roofs; 770.44(A)(4) instead covers clearance for cables on poles and in-span, not above roofs.

Correct: B — 300 mm (12 in.)

Section 770.47(B) sets the default separation for direct-buried conductive optical fiber cable from electric light, power, Class 1, or non-power-limited fire alarm conductors at 300 mm (12 in.). The 6 in. and 24 in. options aren't the code figure, and separation is only waived under the specific raceway/cable-type exceptions in 770.47(B), not for all direct burial.

Correct: C — That the installation also meets 770.110 and 770.113

770.154 states permitted applications are subject to the installation requirements of 770.110 and 770.113 — the table only establishes where a cable type is allowed, not that the installation is automatically compliant. Table 770.154(b) covers substitutions, a separate question, and the code text does not condition compliance on who performs the work.