12.5 Communications, CATV & Optical Fiber Systems (NEC Chapter 8)

12.5 Communications, CATV & Optical Fiber Systems (NEC Chapter 8)

The Low Voltage subject area on the Alabama Electrical Journeyman exam is worth two questions, and it draws on two very different parts of the Code. Section 12.2 covered Article 724 and Article 725 in Chapter 7. This section covers Chapter 8, which behaves unlike anything else in the NEC.

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Why Chapter 8 Stands Alone (NEC 90.3)

Chapter 8 covers communications systems and is not subject to the requirements of Chapters 1 through 7 except where the requirements are specifically referenced in Chapter 8.

Read that literally, because exam questions are built on it. A general rule from Chapter 3 or Article 250 does not automatically apply to a telephone, coaxial, or fiber installation. If Chapter 8 wants a Chapter 1 through 7 rule, it says so. For instance, 800.100 explicitly pulls the grounding electrode system of Article 250 into the bonding requirement; absent that cross-reference, Article 250 would not reach the communications system at all.

The Chapter 8 articles a journeyman meets are:

Since the 2020 edition, Article 800 holds the general rules that apply across all of these systems, and Articles 805, 820, 830, and 840 hold the requirements unique to each.

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Primary Protectors (NEC 805.90)

A primary protector is required on each communications circuit that runs partly outdoors or is subject to accidental contact with light or power conductors over 300 volts to ground. It is the surge and contact-protection device where the outside plant meets the premises wiring, and it must be listed.

• It must be located as close as practicable to the point at which the communications conductors enter the building.
• It must not be located in, or immediately adjacent to, any hazardous (classified) location or near easily ignitible material.
• Its grounding terminal is bonded per 800.100.

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Bonding and Grounding (NEC 800.100 and 250.94)

This is the single most tested part of Chapter 8, because a poorly bonded coaxial or telephone system is the classic path for a lightning surge to enter a house.

The Bonding Conductor (NEC 800.100(A))

Where the 20-foot limit cannot be met in a one- or two-family dwelling, a separate grounding electrode must be driven and bonded to the building's power grounding electrode system with a conductor not smaller than 6 AWG copper. That bonding jumper is essential: an isolated communications ground rod sitting near an unbonded power ground rod creates a lethal difference of potential during a surge. It is never acceptable to leave the two electrode systems unconnected.

Connection Point (NEC 800.100(B))

The bonding conductor must terminate at the intersystem bonding termination required by NEC 250.94, or, in buildings without one, at an accessible point on the grounding electrode system, the grounded interior metal water pipe within 5 ft of entrance, the service accessible means external to enclosures, the metallic service raceway, or the service equipment enclosure.

NEC 250.94 requires that an intersystem bonding termination be provided external to enclosures at the service equipment or meter enclosure and at each disconnecting means for a remote building. It must:

• Be accessible for connection and inspection,
• Have capacity for at least three intersystem bonding conductors, and
• Not interfere with opening the service or meter enclosure.

Three terminals is the design target because a typical dwelling has telephone, cable television, and satellite services arriving separately.

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Separation from Power Conductors (NEC 800.133 / 805.133 / 820.133)

Communications, coaxial, and optical fiber cables must be separated from conductors of electric light, power, Class 1, and non-power-limited fire alarm circuits:

• They must not be placed in any raceway, cable tray, box, enclosure, or cable with those conductors, with narrow exceptions such as where separated by a permanent barrier or listed divider.
• Where they run in the same shaft or parallel to power conductors, they must be separated by at least 2 in. (50 mm) unless the power conductors are in a raceway or in Type AC, MC, MI, or nonmetallic-sheathed cable, or the communications cable is itself in a raceway.
• Communications cables must not be strapped to, or supported by, the raceway of another system.

The hazard is straightforward: 120 or 277 volts crossing into an ungrounded low-voltage cable energizes every handset, modem, television, and thermostat on that system.

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Cable Listings, Substitution, and Removal

The Listing Hierarchy

Each Chapter 8 system has its own listed cable family, and within each family the same plenum over riser over general purpose hierarchy applies:

A higher-rated cable may always substitute downward: plenum cable may be used in a riser or in a general-purpose area, but general-purpose cable may never be installed in a plenum or a riser. For optical fiber, the letter N means nonconductive (no metallic members) and C means conductive (containing a metallic strength member or armor); conductive optical fiber cable must be bonded like any other metallic-membered Chapter 8 cable.

Mechanical Execution and Abandoned Cable

• NEC 800.24, mechanical execution of work: cables must be installed in a neat and workmanlike manner, supported by the building structure, and secured so they are not damaged by normal building use. Cables may not be attached to ceiling grid support wires, exactly as 300.11(B) requires for Class 2 and fire alarm cable.
• NEC 800.25, abandoned cable: the accessible portion of abandoned communications, coaxial, and optical fiber cable must be removed. Decades of dead cable above a suspended ceiling is fuel load with no offsetting benefit, and this rule is why a renovation scope should always include demolition of the old low-voltage plant.