NABCEP Commissioning 2

Question 1

During commissioning of a grid-tied PV system, the installer measures an open-circuit voltage significantly higher than the STC rating. What is the most likely cause?

Accepted Answer

Low ambient temperature increasing Voc

Answer

PV module Voc increases as temperature decreases, so cold ambient conditions can push array voltage well above STC (25°C) nameplate values.

Question 2

Which instrument is most appropriate for verifying that PV source circuits are not cross-connected at the DC combiner box during commissioning?

Accepted Answer

Low-range DC voltmeter with polarity check

Answer

Measuring DC polarity and voltage at each source circuit input confirms correct wiring before energizing the combiner.

Question 3

A commissioning checklist item requires torquing all DC lugs. Why is under-torquing particularly dangerous in a PV system?

Accepted Answer

It can cause high-resistance connections leading to arcing and fire

Answer

Loose connections create resistance, which generates heat and can produce DC arcs that are difficult to extinguish.

Question 4

When commissioning a battery-based off-grid system, what state of charge should the battery bank be at before first connecting PV source circuits?

Accepted Answer

Fully charged to 100% SOC via AC charging

Answer

Manufacturers typically require batteries to be fully charged before initial PV connection to verify charge controller set points and prevent sulfation.

Question 5

During AC-side commissioning, the installer observes that the utility revenue meter is spinning backward before the interconnection agreement is in place. What should be done immediately?

Accepted Answer

Disconnect the system from the grid immediately

Answer

Exporting power before the utility has approved interconnection violates the interconnection agreement and can create safety and billing issues.

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

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

NABCEP Commissioning 2