Communication Systems (Minnesota Class A Journeyworker)

Learning Objectives

Apply the length, separation, and cover limits of 800.44, 800.47, and 800.48 to cables entering a building.

Use Table 810.16(A) and Table 810.52 to size outdoor antenna conductors, and apply the 810.18 clearance rules.

Apply the abandoned-cable definition, the 820.15 power limitation, and the 820.4 alternate wiring method.

Apply Table 830.15 and Table 830.47(A) to network-powered broadband communications systems.

9.1 Scope and Listing (800.1 and 800.2)

Article 800 covers the general requirements for communications system wires and cables outside and entering buildings. Section 800.2 requires listing: communications wires such as distributing frame wire and jumper wire must be listed as resistant to the spread of fire, and for premises-powered broadband systems the network terminal and its grounding means must be listed for that application.

9.2 Wires and Cables Outside and Entering Buildings (800.44 through 800.53)

Overhead, 800.44. Communications cables sharing a pole or running parallel in-span with power conductors must where practicable be located below the power conductors, and must maintain 300 mm (12 in.) of separation at any point in the span, with not less than 1.0 m (40 in.) between the two services at the pole. Above roofs the vertical clearance is 2.5 m (8 ft), and 800.44(E)(1) requires at least 100 mm (4 in.) from power, Class 1, or non-power-limited fire alarm circuit conductors where cables are attached to a building.

Underground, 800.47. Direct-buried communications wires and cables, conductive optical fiber cables, CATV-type coaxial cables, and network-powered broadband cables must be separated at least 300 mm (12 in.) from light or power, non-power-limited fire alarm, or Class 1 circuit conductors; exceptions apply where the conductors are in raceways or have metal cable armor. Direct-buried premise-powered broadband communications cables require a minimum cover of 150 mm (6 in.). Section 800.53 requires at least 1.8 m (6 ft) between lightning protection conductors and communications cables where practicable.

Unlisted cables entering buildings, 800.48. Unlisted outside plant communications cables, unlisted outside plant CATV-type coaxial cables, and unlisted conductive and nonconductive optical fiber cables are permitted in building spaces other than risers and spaces used for environmental air only if all of the following apply: the length of the cable within the building, measured from its point of entrance, does not exceed 15 m (50 ft); and the cable is terminated in an enclosure, on a listed primary protector, or at a grounding block, as applicable.

9.3 Abandoned Cables

Article 100 defines Cable, Abandoned as installed cable that is not terminated at equipment other than a termination fitting or a connector, and is not identified for future use with a tag. The definition imposes no duty itself; its informational note refers the reader to 640.6(B), 645.6(G), 760.25, and 720.25 for the removal requirements. Section 720.25 requires the accessible portion of abandoned cables to be removed. Cable left unterminated and untagged when a riser is replaced is therefore abandoned cable.

The short lengths that appear as wrong answers in Chapter 8 questions belong to other articles: 720.19(A) limits supported conductor length in vertical raceways, 722.171(A)(3) limits exposed power-limited fire alarm cable in nonconcealed spaces, and 750.100(A)(4) sets the bonding conductor length limit for one- and two-family dwellings.

9.4 Antenna Systems — Article 810

Article 810 covers antenna systems, with Part II for receiving equipment and Part III for transmitting and receiving stations. Section 810.12 requires outdoor antennas and lead-in conductors to be securely supported, and prohibits attachment to the electric service mast.

Section 810.16(A) sizes receiving station outdoor antenna conductors.

Material (Receiving Station)	Less Than 11 m (35 ft)	11 m to 45 m (35 ft to 150 ft)	Over 45 m (150 ft)
Aluminum alloy, hard-drawn copper	19 AWG	14 AWG	12 AWG
Copper-clad steel, bronze, or other high-strength material	20 AWG	17 AWG	14 AWG

Section 810.18(A) governs lead-in conductors attached to buildings: they must be installed so that they cannot swing closer than 600 mm (2 ft) to conductors of circuits of 250 volts or less between conductors, or 3.0 m (10 ft) to conductors of circuits over 250 volts between conductors. Where all conductors are supported to ensure permanent separation, the clearance for circuits not over 150 volts may be reduced, but not below 100 mm (4 in.), and the clearance to a lightning protection conductor must be not less than 1.8 m (6 ft).

9.5 CATV and Radio Distribution — Article 820

Article 820 covers coaxial cable distribution of radio frequency signals employed in community antenna television (CATV) systems. Section 820.4, Alternate Wiring Methods, permits network-powered broadband wiring methods to substitute for the wiring methods of Article 820.

Section 820.15 permits coaxial cable to deliver power to equipment directly associated with the radio frequency distribution system if the voltage is not over 60 volts and the current is supplied by a transformer or other device having power-limiting characteristics, and requires power to be blocked from premises devices not intended to be powered via the coaxial cable.

9.6 Network-Powered Broadband Systems — Article 830

Table 830.15 classifies network power sources.

Network Power Source	Low Power	Medium Power
Circuit voltage, Vmax (volts)	0–100	0–150
Power limitation, VAmax (volt-amperes)	250	250
Current limitation, Imax (amperes)	1000/Vmax	1000/Vmax
Maximum power rating (volt-amperes)	100	100

Two points matter: VAmax is 250 volt-amperes for both classes, so it does not separate low power from medium power, and Imax is the formula 1000/Vmax, so 1000 is a numerator rather than a power limitation. Under 830.15(2), dc sources over 150 volts to ground but not more than 200 volts to ground with current to ground limited to 10 mA dc are medium-power sources.

Section 830.44 governs overhead spans, which must clear finished grade by 2.9 m (9 1/2 ft), residential property and driveways by 3.5 m (11 1/2 ft), and public streets by 4.7 m (15 1/2 ft). Spans without an outer jacket attached to a building must be kept not less than 900 mm (3 ft) from windows designed to be opened.

Location of Wiring Method or Circuit	Direct Burial Cables	RMC or IMC	Nonmetallic Raceways Listed for Direct Burial
All locations not specified below	450 mm (18 in.)	150 mm (6 in.)	300 mm (12 in.)
Under a building (in raceway only)	0	0	0

Section 830.47(B) prohibits attaching network-powered broadband cables to the exterior of a raceway as a means of support. The direct-buried cable column of Table 300.7(A) for general wiring is not the cover table for these cables.

Code Navigation

Topic	NEC Section	What It Contains
Scope and listing	800.1, 800.2	Cables outside and entering buildings; listing
Overhead wires and cables	800.44	300 mm (12 in.) in-span separation; 2.5 m (8 ft) above roofs; 100 mm (4 in.) on buildings
Underground systems	800.47	300 mm (12 in.) direct-burial separation; 150 mm (6 in.) premise-powered cover
Unlisted cables entering buildings	800.48	15 m (50 ft) limit from the point of entrance
Antennas	Table 810.16(A), 810.52, 810.18	20/17/14 AWG high-strength sizes; 600 mm (2 ft) and 3.0 m (10 ft) clearances
Network-powered broadband	Table 830.15, 830.44, Table 830.47(A)	250 volt-amperes; 900 mm (3 ft) from windows; 450 mm (18 in.) cover

Common Exam Traps

Reading the wrong length limit out of 800.48. The limit is 15 m (50 ft) from the point of entrance, not 3.0 m (10 ft) and not 30 m (100 ft).

Confusing Article 800 and Article 830 underground numbers. Section 800.47(B) separation is 300 mm (12 in.), the cover for direct-buried premise-powered broadband cables is 150 mm (6 in.), the general cover under Table 830.47(A) is 450 mm (18 in.), and 900 mm (3 ft) is a clearance from windows, not an underground separation.

Mixing the two rows of Table 810.16(A). Below 11 m (35 ft), aluminum alloy and hard-drawn copper take 19 AWG while copper-clad steel, bronze, and other high-strength material take 20 AWG.

Applying the 600 mm (2 ft) lead-in clearance to the wrong circuit. Section 810.18(A) uses 600 mm (2 ft) for circuits of 250 volts or less, 3.0 m (10 ft) for circuits over 250 volts, and 1.8 m (6 ft) to lightning protection conductors.

Practical Field Points

Measure the 15 m (50 ft) of unlisted outside plant cable from the point of entrance.

Remove accessible abandoned cable when a riser or distribution frame is replaced; untagged, unterminated cable is abandoned cable under the Article 100 definition.

Keep overhead network-powered broadband spans without an outer jacket 900 mm (3 ft) from operable windows, and support them independently of raceways.

Summary

Article 800 governs communications system wires and cables outside and entering buildings. Section 800.44 controls overhead work with 300 mm (12 in.) of separation from power conductors in the span, 1.0 m (40 in.) between services at the pole, 2.5 m (8 ft) above roofs, and 100 mm (4 in.) from power conductors where cables are attached to a building. Section 800.47 controls underground work with 300 mm (12 in.) of direct-burial separation from light, power, non-power-limited fire alarm, and Class 1 conductors and 150 mm (6 in.) of cover for direct-buried premise-powered broadband cables. Section 800.48 allows unlisted outside plant cable only where the length within the building does not exceed 15 m (50 ft) from the point of entrance and the cable is terminated on a listed primary protector, a grounding block, or an enclosure. Cable not terminated at equipment is abandoned cable under the Article 100 definition, and the removal rules it references appear in 640.6(B), 645.6(G), 760.25, and 720.25. Article 810 sizes antenna conductors from Table 810.16(A) and Table 810.52 and sets the 810.18(A) clearances of 600 mm (2 ft), 3.0 m (10 ft) and 1.8 m (6 ft) to lightning protection conductors. Article 820 limits coaxial power delivery to not over 60 volts under 820.15 and permits network-powered broadband wiring methods to substitute under 820.4. Article 830 classifies sources through Table 830.15, where low power is 0–100 volts and medium power is 0–150 volts with 250 volt-amperes of VAmax in both classes, and Table 830.47(A) begins at 450 mm (18 in.) of cover for direct-burial cables.

Communication Systems