C7 Testing & Commissioning Procedures 3 — Questions and Answers
Question 1: During commissioning of a structured cabling system, what does a channel test measure compared to a basic link test?
- Channel includes the patch cords at both ends; basic link excludes them (Correct answer)
- Channel tests only the horizontal run; basic link includes MDF equipment
- Channel measures frequency only; basic link measures resistance only
- Channel requires a fiber OTDR; basic link uses a copper tester
Correct answer: Channel includes the patch cords at both ends; basic link excludes them
A channel test encompasses the complete end-to-end path including patch cords, while a basic link tests only the permanent (installed) cable segment.
Question 2: What is the purpose of performing an earth ground resistance test at a low-voltage system installation?
- To verify lightning surge suppressor clamping voltage
- To confirm the grounding electrode resistance meets NEC requirements (typically ≤25 Ω) (Correct answer)
- To measure the neutral-to-ground voltage at the panel
- To check cable shield continuity to rack ground
Correct answer: To confirm the grounding electrode resistance meets NEC requirements (typically ≤25 Ω)
A fall-of-potential or clamp-on earth test confirms the grounding electrode resistance is ≤25 Ω per NEC 250.53, ensuring effective fault current dissipation.
Question 3: A technician notices that a fiber optic link shows higher insertion loss than the calculated budget. Which commissioning tool best identifies the location of the excess loss?
- Power meter and light source
- Optical time-domain reflectometer (OTDR) (Correct answer)
- Visual fault locator (VFL)
- Network protocol analyzer
Correct answer: Optical time-domain reflectometer (OTDR)
An OTDR traces the fiber and displays a backscatter profile, pinpointing connectors, splices, or bends contributing excess loss with distance markers.
Question 4: During commissioning of a distributed antenna system (DAS), what does passive intermodulation (PIM) testing detect?
- Antenna azimuth alignment error
- Unwanted interference products generated by nonlinear passive components (Correct answer)
- Cable impedance mismatch at the head end
- Signal-to-noise ratio at the donor antenna
Correct answer: Unwanted interference products generated by nonlinear passive components
PIM testing sends two high-power tones through passive components (connectors, cables, antennas) and measures interference products that can desensitize receivers.
Question 5: When commissioning a two-way radio (BDA/DAS) system in a California high-rise, the system must demonstrate what minimum signal strength inside the building?
- -70 dBm RSSI on 90% of the floor area on 95% of floors (Correct answer)
- -85 dBm RSSI on 80% of the floor area on 90% of floors
- -95 dBm RSSI on 75% of the floor area on 85% of floors
- -60 dBm RSSI on 100% of the floor area on 100% of floors
Correct answer: -70 dBm RSSI on 90% of the floor area on 95% of floors
California Fire Code (per NFPA 1 and local amendments) generally requires −70 dBm on 90% of floor area on 95% of floors for in-building radio coverage.
Question 6: What is the purpose of a soak test during low-voltage system commissioning?
- To stress-test cables with elevated voltage for insulation breakdown
- To run the system under normal operating conditions for an extended period to reveal intermittent faults (Correct answer)
- To measure current draw at maximum load for 60 seconds
- To verify the UPS transfers to battery within the specified switchover time
Correct answer: To run the system under normal operating conditions for an extended period to reveal intermittent faults
A soak test operates the system continuously for hours or days, allowing thermal cycling and load variations to expose latent intermittent defects.
Question 7: A commissioning checklist for a security video system requires verifying frame rate under storage load. What tool is used to measure actual recorded frames per second?
- Cable certifier
- VMS playback analysis or diagnostic dashboard (Correct answer)
- Optical power meter
- Protocol analyzer with SNMP traps
Correct answer: VMS playback analysis or diagnostic dashboard
The video management software (VMS) diagnostic dashboard or playback metadata confirms actual recorded FPS versus the configured target under storage I/O load.
C7 Testing & Commissioning Procedures 3
During commissioning of a structured cabling system, what does a channel test measure compared to a basic link test?