C7 CATV, Satellite & Antenna Systems (NEC Articles 810 & 820) — Questions and Answers
Question 1: NEC Article 820 governs the installation of which type of low voltage system?
- Structured data cabling (Cat 5e/6/6A)
- Community antenna television (CATV) and coaxial cable systems (Correct answer)
- Class 2 remote-control signaling circuits
- Optical fiber communication cables
Correct answer: Community antenna television (CATV) and coaxial cable systems
NEC Article 820 specifically covers Community Antenna Television (CATV) and radio distribution systems using coaxial cable. Data cabling is covered under Article 800, fiber under Article 770, and remote-control circuits under Article 725.
Question 2: Per NEC Article 820, where must the coaxial cable from a CATV service be grounded when it enters a building?
- At the first splitter inside the building
- At the cable company's pedestal at the street
- At the point of entry to the building, as close as practicable (Correct answer)
- Grounding is optional for CATV coaxial cable
Correct answer: At the point of entry to the building, as close as practicable
NEC 820.93 requires that the outer conductive shield of the coaxial cable be grounded as close as practicable to the point where the cable enters the building. This protects against lightning surges and static buildup traveling on the cable shield from outdoors.
Question 3: When installing a satellite dish on a residential rooftop, per NEC Article 810, the mast and mounting structure must be:
- Bonded to the building's grounding electrode system (Correct answer)
- Connected to a separate ground rod isolated from the electrical system
- Left ugrounded since satellite signals are high frequency
- Grounded only if the dish exceeds 3 feet in diameter
Correct answer: Bonded to the building's grounding electrode system
NEC Article 810.21 requires the antenna mast and associated equipment to be bonded to the building's grounding electrode system. Using an isolated separate rod is a code violation — all grounding electrodes must be bonded together to prevent dangerous voltage differences during a lightning event.
Question 4: A CATV distribution system uses a two-way splitter at the point of entry to serve two TVs. Each two-way splitter introduces approximately how much signal loss?
- 1 dB
- 3.5 dB (Correct answer)
- 10 dB
- 20 dB
Correct answer: 3.5 dB
A two-way splitter introduces approximately 3.5 dB of insertion loss (theoretically 3 dB for the power split plus ~0.5 dB of passive loss). This loss accumulates with each additional splitter, which is why signal levels must be calculated for CATV distribution systems to ensure adequate signal strength at the last outlet.
Question 5: Which coaxial cable type is the current standard recommended for CATV, satellite, and over-the-air antenna installations in new residential construction?
- RG-59 (75 ohm)
- RG-6 (75 ohm) (Correct answer)
- RG-8 (50 ohm)
- RG-58 (50 ohm)
Correct answer: RG-6 (75 ohm)
RG-6 (75-ohm) is the current standard for residential CATV, satellite, and antenna wiring. It has a larger center conductor and thicker dielectric than RG-59, resulting in lower signal loss especially at higher frequencies (satellite bands). RG-8 and RG-58 are 50-ohm cables used in radio/RF applications, not CATV.
Question 6: Per NEC Article 820.44, CATV coaxial cable installed in a plenum ceiling must be listed as which cable type?
- CATV (basic coaxial, no plenum rating required)
- CATVP (plenum-rated coaxial) (Correct answer)
- CATVR (riser-rated coaxial)
- Any coaxial cable in conduit satisfies the requirement
Correct answer: CATVP (plenum-rated coaxial)
NEC Article 820.44 requires CATVP (Community Antenna Television Plenum) rated cable in plenum spaces. CATVP cables have fluoropolymer or other low-smoke jacket materials required in air-handling spaces. CATVR is for riser (vertical shaft) use, and unrated CATV cable cannot be used in plenums even in conduit unless the conduit is metal.
C7 CATV, Satellite & Antenna Systems (NEC Articles 810 & 820)
NEC Article 820 governs the installation of which type of low voltage system?