C7 Grounding & Bonding for Low Voltage Systems 2 — Questions and Answers
Question 1: Which ANSI/TIA standard specifically addresses telecommunications grounding and bonding for commercial buildings?
- ANSI/TIA-568
- ANSI/TIA-607 (Correct answer)
- ANSI/TIA-569
- ANSI/TIA-942
Correct answer: ANSI/TIA-607
ANSI/TIA-607 is the dedicated standard for telecommunications bonding and grounding planning and installation methods in commercial buildings.
Question 2: What does the acronym 'TMGB' stand for in telecommunications grounding infrastructure?
- Terminal Mounted Ground Bus
- Telecommunications Main Grounding Busbar (Correct answer)
- Twisted Multi-Grade Bonding conductor
- Total Mechanical Ground Bonding system
Correct answer: Telecommunications Main Grounding Busbar
TMGB stands for Telecommunications Main Grounding Busbar, which serves as the primary grounding point connecting the telecommunications system to the building's electrical ground.
Question 3: Per NEC Article 800, how must the grounding conductor for a communications cable entering a building be terminated?
- To the nearest metal water pipe or gas line
- To the building's grounding electrode system or an acceptable NEC Article 250 grounding electrode (Correct answer)
- To the closest AC outlet equipment grounding conductor
- To the metallic shield of the incoming cable only
Correct answer: To the building's grounding electrode system or an acceptable NEC Article 250 grounding electrode
NEC Article 800 requires that communications cable grounding conductors connect to the building's established grounding electrode system or an electrode permitted by Article 250.
Question 4: If a single ground rod electrode measures greater than what resistance value must a second grounding electrode be installed per NEC 250.56?
- 10 ohms
- 25 ohms (Correct answer)
- 50 ohms
- 100 ohms
Correct answer: 25 ohms
Per NEC 250.56, if a single ground rod has resistance to ground exceeding 25 ohms, an additional grounding electrode must be installed to achieve adequate grounding.
Question 5: What is a 'telecommunications bonding backbone' (TBB) in a multi-story building?
- The main coaxial distribution cable for a CATV system
- A conductor that interconnects all telecommunications grounding busbars (TGBs) to the main TMGB throughout the building (Correct answer)
- The primary fiber optic backbone cable between floors
- A ground cable installed only on the exterior of the building
Correct answer: A conductor that interconnects all telecommunications grounding busbars (TGBs) to the main TMGB throughout the building
The telecommunications bonding backbone (TBB) is a dedicated conductor that connects all floor-level TGBs back to the main TMGB, creating a continuous bonding path throughout the building.
Question 6: Per NEC Table 250.66, what factor determines the sizing of the grounding electrode conductor (GEC)?
- The total number of circuits in the building
- The size of the largest service entrance conductor or equivalent area for parallel conductors (Correct answer)
- The physical distance from the service panel to the grounding electrode
- The voltage rating of the electrical service
Correct answer: The size of the largest service entrance conductor or equivalent area for parallel conductors
NEC Table 250.66 sizes the grounding electrode conductor based on the size of the largest service entrance conductor, ensuring the GEC can carry adequate fault current.
Question 7: Which grounding and protection requirement applies to exterior antenna systems installed on a building per NEC Article 810?
- Antennas must use a dedicated 20-amp grounded circuit
- An antenna discharge unit must be installed and connected to an acceptable grounding electrode conductor (Correct answer)
- Exterior antennas must be bonded only to the metal roof structure
- Antenna grounding is optional if the antenna is below 30 feet in height
Correct answer: An antenna discharge unit must be installed and connected to an acceptable grounding electrode conductor
NEC Article 810 requires exterior antenna systems to include an antenna discharge unit (lightning arrester) and a properly sized grounding electrode conductor to protect against lightning transients.
C7 Grounding & Bonding for Low Voltage Systems 2
Which ANSI/TIA standard specifically addresses telecommunications grounding and bonding for commercial buildings?