NABCEP Commissioning 3 — Questions and Answers
Question 1: Which NEC article governs the labeling requirements that must be verified during PV system commissioning?
- Article 690 (Correct answer)
- Article 705
- Article 480
- Article 310
Correct answer: Article 690
NEC Article 690 contains all PV-specific installation and labeling requirements, including mandatory warning labels at disconnects and combiner boxes.
Question 2: During commissioning, an insulation resistance test on a PV source circuit reads 0.5 MΩ at 500 V. How should the installer interpret this result?
- Acceptable — above 1 kΩ per volt is sufficient
- Borderline — monitor but proceed
- Unacceptable — investigate for ground fault or damaged insulation (Correct answer)
- Normal for wet conditions — retest when dry
Correct answer: Unacceptable — investigate for ground fault or damaged insulation
Industry practice requires insulation resistance values well above 1 MΩ; 0.5 MΩ suggests damaged insulation or a ground fault that must be corrected.
Question 3: What is the purpose of recording I-V curve data during PV system commissioning?
- To set the inverter's MPPT frequency
- To establish a performance baseline for future degradation comparison (Correct answer)
- To satisfy utility net metering billing requirements
- To calibrate the ground fault detection circuit
Correct answer: To establish a performance baseline for future degradation comparison
I-V curve measurements at commissioning serve as the baseline against which future measurements are compared to detect degradation or faults.
Question 4: A commissioning technician finds that PV module frames are not bonded to the racking system. Which code section is violated?
- NEC 690.43 — Equipment Grounding (Correct answer)
- NEC 690.35 — Ungrounded Systems
- NEC 705.12 — Load-Side Connections
- NEC 690.13 — Disconnecting Means
Correct answer: NEC 690.43 — Equipment Grounding
NEC 690.43 requires that non-current-carrying metal parts of PV modules and equipment be bonded to the equipment grounding system.
Question 5: When performing a functional test of a DC arc fault circuit interrupter (AFCI) during commissioning, what is the expected outcome?
- The inverter output power increases by 10%
- The AFCI trips and must be manually reset after the test (Correct answer)
- The array voltage drops to zero automatically
- The ground fault LED illuminates on the combiner
Correct answer: The AFCI trips and must be manually reset after the test
A successful AFCI self-test or trip test causes the device to open the circuit and require a manual reset, confirming protective function.
Question 6: During commissioning of a roof-mounted residential system, the installer cannot locate the required rapid shutdown initiation device. What should happen?
- Proceed — rapid shutdown only applies to commercial systems
- Document the omission and commission the system provisionally
- Do not commission the system until the RSD device is installed and labeled (Correct answer)
- Bypass the RSD and note it for a future service call
Correct answer: Do not commission the system until the RSD device is installed and labeled
NEC 690.12 requires rapid shutdown systems on all rooftop PV systems; the system must not be commissioned without this required safety equipment in place.
Question 7: What reading should a clamp-on DC ammeter show on a shaded string during peak sun hours compared to an unshaded string of identical modules?
- Higher current due to voltage redistribution
- Lower current proportional to the degree of shading (Correct answer)
- Identical current because bypass diodes compensate fully
- Zero current because shading triggers string protection
Correct answer: Lower current proportional to the degree of shading
Shading reduces short-circuit current (Isc) in the affected cells, so the entire shaded string produces less current than an unshaded string.
NABCEP Commissioning 3
Which NEC article governs the labeling requirements that must be verified during PV system commissioning?