LVC-2 — Communications Systems

Exam checkpoints

Put the system in the right scope

Article 800 covers communications circuits and equipment within its NEC scope. A telephone pair, Ethernet cable, coaxial cable, optical fiber, and powered broadband cable are not automatically governed by one identical rule. Article 770 applies to optical fiber portions, Article 820 to community antenna television and radio-distribution coaxial systems, Article 830 to network-powered broadband, and Article 840 to premises-powered broadband. Class 2 or Class 3 control circuits remain under Article 725 unless a permitted combination changes their classification.

Section 90.2(B)(4) excludes specified communications-utility installations under exclusive utility control in the locations described by the rule, such as outdoors or in building spaces used exclusively for those installations. That exclusion is not a blanket statement that every carrier-owned cable anywhere in a customer's building is outside the NEC. Establish the demarcation, ownership, control, and physical location, then apply Article 800 to the premises installation that remains within scope.

The network interface is also not permission to ignore Chapters 1 through 4. Article 800 supplements or modifies general rules where stated. Hazardous locations, environmental-air spaces, fire-rated penetrations, mechanical protection, working space, and listing instructions can invoke other articles.

Protect the building entrance

Outside communications conductors can be exposed to lightning or accidental contact with power conductors. Section 800.90 requires a listed primary protector for exposed circuits under its conditions. Locate the protector as close as practicable to the point where the cable enters the building and do not place avoidable unprotected cable deep inside the premises. A protector is not required merely because an entirely interior patch cable connects two rooms.

Bond the primary protector and metallic cable members under 800.100. The bonding conductor or grounding electrode conductor is copper or another corrosion-resistant conductive material, not smaller than 14 AWG, as short and straight as practicable, and protected from physical damage. In a one- or two-family dwelling, its normal maximum length is 20 ft. It is not required to be larger than 6 AWG. A metal raceway enclosing it is bonded at both ends to avoid adding impedance.

Where the building has an intersystem bonding termination under 250.94, use that point. Otherwise connect to the nearest accessible grounding means permitted by 800.100, such as the building grounding electrode system, service equipment enclosure, grounding electrode conductor, or another listed point in the section. Do not create an isolated communications rod and leave it unbonded to the power grounding electrode system. A separate electrode, where permitted because the normal path is impracticable, is bonded to the building electrode system.

Grounding here limits voltage differences and gives lightning or accidental-contact current a coordinated path. It does not make communication pairs ordinary equipment grounding conductors or eliminate surge-protection design. Keep bends gentle and the path direct because a long coiled conductor has high surge impedance even if its dc resistance is low.

Select cable for the space

The cable suffix is a fire-performance and application marking. CMP is plenum communications cable, CMR is riser cable, CMG and CM are general-purpose communications cables, and CMX is limited-use cable. Section 800.154 provides the application and substitution hierarchy: a higher fire-performance listing can substitute downward where the table permits, but CM or CMX does not become plenum cable because the run is short.

In an environmental-air plenum described by 300.22(C), use Type CMP cable or a permitted raceway or cable-routing method identified by the rule. In a vertical riser, use CMR, CMP, or another permitted protected method. A metallic raceway can change the permitted cable arrangement only when the applicable table and raceway rule say so. Verify the printing on the cable jacket instead of relying on its color.

Section 800.25 requires removal of the accessible portion of abandoned communications cable. Cable reserved for future use is not abandoned when identified with a durable tag suitable for the environment. Cutting both ends and leaving coils above a ceiling does not satisfy the rule. Under 800.26, penetrations through fire-resistance-rated walls, floors, or ceilings are firestopped by an approved system that maintains the assembly rating.

Separate communications from power

Section 800.133 generally prohibits communications conductors in the same raceway, compartment, outlet box, junction box, or similar enclosure with electric light, power, Class 1, non-power-limited fire alarm, or medium-power network-powered broadband conductors. A permanent barrier or listed divider is one exception. Where power enters an enclosure solely to supply communications distribution equipment, the rule permits a conditioned arrangement with at least 1/4 in. internal separation.

In other applications, communications cable is generally separated at least 2 in. from those power conductors. Separation is not required where the power conductors are in a raceway or qualifying jacketed cable, where the communications conductors are in raceway, or where a continuous firmly fixed nonconductor provides the specified separation. The 2-in. rule is therefore a starting rule with defined exceptions—not permission to share an unpartitioned power raceway.

Cross power conductors as nearly at right angles as practical and preserve physical separation to reduce induced noise, but recognize that signal-performance practices can be stricter than the NEC safety minimum. Power over Ethernet also adds cable heating and bundle considerations under the applicable 2017 power-delivery rules; a communications listing is not unlimited ampacity.

Support and protect the pathway

Section 800.24 requires neat, workmanlike installation. Exposed cables on ceilings and sidewalls are supported by the building structure with hardware designed not to damage the cable. Apply 300.11 in accessible ceiling spaces. Do not drape cable across ceiling tiles, rest it on ductwork, or use ordinary grid wires as support. Nonmetallic cable ties and supports in environmental-air spaces need the applicable low-smoke and heat-release listing.

Section 800.133 also prohibits strapping, taping, or attaching communications cable to the exterior of a raceway as a means of support, apart from the stated aerial-mast exception. Maintain bend radius and pulling tension, protect cable at sharp metal edges, firestop penetrations, label both ends, preserve access panels, and keep terminations in listed equipment. Final inspection follows the path from entrance protector and bond through cable marking, separation, support, fire barriers, abandoned cable, and the outlet or equipment listing.