NABCEP Electrical Component Inspection 3

Question 1

During inspection of a battery-based PV system, you find that the battery bank negative terminal is directly bonded to the equipment grounding conductor at the charge controller. According to NEC Article 690, what type of system is this?

Accepted Answer

A solidly grounded DC system

Answer

A solidly grounded DC system has one conductor of the circuit directly connected to the grounding electrode system without any impedance.

Question 2

An inspector observes that a string of 10 modules in series produces 380V Voc at STC but only 310V during morning inspection. What is the most likely cause?

Accepted Answer

The system has a partial shading condition or failed module

Answer

A significantly lower-than-expected string Voc during clear conditions typically indicates a failed module or partial shading that reduces voltage contribution from part of the string.

Question 3

During a thermal imaging inspection of PV modules, you identify a cell-level hot spot that is 40°C above surrounding cells. What is the most probable root cause?

Accepted Answer

A cracked or degraded cell with increased series resistance

Answer

Cell-level hot spots indicate locally increased resistance, most commonly from cracked cells, delamination, or soiling that causes current to flow through a high-resistance path.

Question 4

An inspector finds that the service entrance panel where the PV system interconnects has a main breaker rated at 200A and the bus bar is also rated at 200A. The PV interconnection breaker is 40A. Does this installation comply with NEC 705.12(B)(2)?

Accepted Answer

No, the PV breaker must be located at the opposite end from the main breaker

Answer

NEC 705.12(B)(2) requires the PV supply-side breaker to be at the opposite end of the bus from the main breaker when using the 120% rule, to limit worst-case bus loading.

Question 5

During inspection, you measure insulation resistance of a PV array using a megohmmeter and find a reading of 0.5 MΩ between the positive conductor and ground. What does this indicate?

Accepted Answer

Significant insulation degradation requiring further investigation

Answer

A megohmmeter reading of 0.5 MΩ is far below the minimum acceptable insulation resistance (typically ≥1 MΩ for PV systems), indicating compromised insulation that must be investigated.

(NABCEP) Certified North American Board of Certified Energy Practitioners Specialist Practice Test

(NABCEP) Certified North American Board of Certified Energy Practitioners Specialist Practice Test

NABCEP Electrical Component Inspection 3