Communications Systems practice questions

Correct: B — It is exposed to accidental contact with power conductors operating at over 300 volts to ground

805.90(A) requires a primary protector on any circuit within the block, aerial or underground, that is exposed to accidental contact with power conductors over 300 volts to ground. Length, building frame material, and conduit type are not the triggers named in this section.

Correct: D — No, passing through masonry is one of the listed exceptions to the bushing requirement

Per 805.50(C)(1), the insulating bushing is not required where the entering wires and cables pass through masonry — this is one of four independent exceptions, not something that depends on sheath type or protector omission.

Correct: B — At least 100 mm (4 in.), or a continuous fixed nonconductor separating the two

805.50(B) sets the baseline separation at 100 mm (4 in.) from open electric light or power conductors, or a continuous, firmly fixed nonconductor such as porcelain tubing as an alternative. There's no 12-inch minimum in this rule, listing of the cable doesn't waive separation, and the requirement isn't limited to conductors over 600 volts.

Correct: B — 805.90(A)(1)

805.90(A)(1) lists the five conditions under which fuseless-type primary protectors are permitted. 805.90(A)(2) instead governs fused-type protectors, used when none of the 805.90(A)(1) conditions are met, and 805.93(A) covers sheath grounding at building entry, not protector type selection.

Correct: C — 805.90(B)

805.90(B) is the Location rule, requiring the primary protector to be in, on, or immediately adjacent to the structure and as close as practicable to the point of entrance. 805.50(C) instead governs how the communications wire/cable itself enters the building, and 805.170(A) just lists primary protectors as a required protector type without addressing placement.

Correct: D — They must be listed as either a primary or secondary protector

805.170 requires protectors to be listed in accordance with 805.170(A) (primary) or 805.170(B) (secondary). There's no field-test or case-by-case AHJ approval path in this section, and wet-location identification isn't the qualifying requirement here.

Correct: B — As close as practicable to the point of entrance

805.93(A) requires the grounding, bonding, or interruption to be as close as practicable to the point of entrance — not tied to panelboard location, end equipment, or a fixed 6 ft distance from the grounding electrode system.

Correct: A — A coaxial cable listed for plenum use

820.154 allows a coax cable with a more stringent listing to replace one with a less stringent listing, so plenum-rated coax can stand in for riser-rated coax. The CMR-rated communications cable fails because 820.154 requires the substitute to be coaxial-type, not a communications cable. The limited-use coax is a lower rating than riser, so it can't substitute upward. Any riser-rated cable regardless of type ignores the coax-only requirement.

Correct: D — As close as practicable to the entrance point, or integral to the ground block

820.93(C) requires the primary protector to be located as close as practicable to the cable's entrance point, on either side, or integral to the ground block. Placing it elsewhere in the building or tying its location to service equipment or receptacle spacing are not the rule in this section.

Correct: C — No, cord-and-plug connections are not permitted for this grounding path

820.100 explicitly permits connecting to the equipment grounding conductor through a grounded receptacle using a dedicated bonding jumper and a permanently connected listed device, but states that use of a cord and plug for this connection is not permitted. The grounded-receptacle option itself is allowed when done with a permanent, listed device — it's specifically the cord-and-plug method that's barred.

Correct: D — No, because the conductor is grounded and interrupted, the aerial-outside-block trigger does not apply

830.90(A) requires primary protection on conductors that are neither grounded nor interrupted and run partly or entirely in aerial cable not confined within a block. Since this conductor is grounded and interrupted, that trigger doesn't apply, regardless of whether it's aerial or outside the block.

Correct: A — 4.7 m (15½ ft)

Per 830.44(B)(3), areas subject to truck traffic — including parking areas, public streets, and similar vehicle-traversed land — require 4.7 m (15½ ft) of clearance. The 3.5 m distance only applies to residential property, driveways, and commercial areas NOT subject to truck traffic, and 2.9 m applies only to pedestrian-only walkways.

Correct: D — Type BMU

830.179(B) requires Type BMU cable to be jacketed and listed as suitable for outdoor underground use for medium-power circuits. Type BLU is the low-power counterpart under 830.179(C), a generic 300-volt-rated jacketed coax isn't automatically underground-listed, and the pre-2000 CATV exemption in 830.179 only excuses old low-power coax from the listing requirement — it doesn't qualify as underground-rated new construction.

Correct: B — The current to ground is limited to 10 mA dc, and it meets Table 830.15's current and power limits for medium-power sources

830.15(2) allows DC sources exceeding 150 V to ground but not more than 200 V to ground to be classified as medium-power only if the current to ground is limited to 10 mA dc AND the source meets Table 830.15's current and power limitations for medium-power sources. 150 V doesn't disqualify it — that's the whole point of the exception — and UL 60950-21 is referenced only as a listing standard, not a substitute for meeting the classification criteria.

Correct: B — A Class 2 remote-control circuit cable

830.133(A)(1)(d) bars medium-power network-powered broadband cables from sharing a raceway, tray, box, or enclosure with Class 2 or Class 3 circuits, or with power-limited fire alarm circuits. Broadband cables (low- or medium-power) may share space with each other per 830.133(A)(1)(a).

Correct: A — 830.93(A)

830.93(A) governs grounding or interruption of the shield and metallic members where the cable enters the building, requiring it as close as practicable to the point of entrance. 830.93(B) is the parallel rule for cables terminated outside the building at the NIU, and 830.47(A) only addresses physical damage protection for underground cables, not grounding.

Correct: B — On the network side of the NIU, on the external cable

Under 830.90(B)(1), a listed primary protector applied externally must be on each network-powered broadband cable external to and on the network side of the NIU. Placing it only on the derived (output) circuit side matches a different, separately listed option under 830.90(B)(3), not the general external-protector case. Just grounding it anywhere in the building, or assuming any NIU enclosure qualifies, ignores the listing and location requirements in 830.90(B).

Correct: C — 830.47(A)

Table 830.47(A), Network-Powered Broadband Communications Systems Minimum Cover Requirements, lives at 830.47(A), which governs direct-buried cable cover depths. 830.44(B) instead addresses overhead cable clearance from ground, not burial depth, so it can't answer a direct-burial cover question.

Correct: B — No, raceways are to be used for their intended purpose and cannot be used as a support means for the cable

Per 830.133(B), raceways must be used only for their intended purpose, and network-powered broadband communications cables cannot be strapped, taped, or otherwise attached to the exterior of a conduit or raceway as a means of support. Power level, tape rating, and grounding/bonding status don't change this restriction.

Correct: B — Whatever grounding means is covered by the product's listing

840.170(A) states there are no requirements on the network terminal and its grounding methodologies except for those covered by the listing of the product — Article 250 electrode rules, 800.100 primary protector grounding, and a dedicated grounding electrode conductor are not imposed here.

Correct: A — The network terminal is served by a nonconductive optical fiber cable and the circuit stays entirely inside the building

840.101 applies when the network terminal is fed by nonconductive optical fiber (or a conductive fiber cable's metal member is broken by an insulating joint) and the circuits from that terminal are completely contained within the building. A circuit that leaves the building, or a fully conductive fiber cable with no interruption, doesn't trigger this section; the number of coax circuits is irrelevant.

Correct: B — It is not required to be grounded

840.101(B) states plainly that communications circuits shall not be required to be grounded. There is no exception carving out commercial occupancies, no mandatory point-of-entrance grounding, and no blanket bonding-to-shield requirement in this section.

Correct: B — 805.90 and 805.93

840.94 states that once a circuit leaves the building to power remote equipment or exits the 46 m (150 ft) rolling-sphere zone of protection, 805.90 and 805.93 apply. It's not that Article 840 keeps governing unchanged, and it's not just the listing rule alone — both the listing (805.90) and protector (805.93) requirements kick in together.

Correct: A — Nothing additional — 725.144 compliance is not required at this current

840.160 waives the 725.144 compliance requirement for listed 4-pair communications cables when the power source's rated current does not exceed 0.3 A in any 24 AWG or larger conductor. At 0.25 A, that threshold isn't met, so no additional bundling compliance is required. The other choices misstate the rule as unconditional or invent unrelated requirements.

Correct: C — 6 A

Ohm's law: I = V ÷ R = 120 ÷ 20 = 6 A. The distractors multiply or invert V and R, or slip a decimal.