NABCEP Grid Interconnection 1 — Questions and Answers
Question 1: What is the primary standard that defines technical requirements for interconnecting distributed energy resources, including solar PV systems, to the electric power system?
- NEC Article 690
- IEEE 1547-2018 (Correct answer)
- UL 1741
- NFPA 70E
Correct answer: IEEE 1547-2018
IEEE 1547 is the nationally recognized standard governing the technical interconnection requirements for distributed energy resources such as solar PV systems.
Question 2: Anti-islanding protection in grid-tied inverters is designed to:
- Prevent power outages during thunderstorms
- Shut down the inverter when grid power is lost to protect utility workers (Correct answer)
- Allow the system to power critical loads during grid failures
- Regulate the frequency of electricity exported to the grid
Correct answer: Shut down the inverter when grid power is lost to protect utility workers
Anti-islanding protection prevents the inverter from continuing to energize the grid during an outage, protecting utility linemen performing repairs on de-energized lines.
Question 3: The Point of Common Coupling (PCC) in a grid-tied PV system is:
- The junction box on the back of each solar module
- The location where the PV system electrically connects to the utility distribution network (Correct answer)
- The main service panel breaker box inside the home
- The combiner box where multiple PV strings are joined
Correct answer: The location where the PV system electrically connects to the utility distribution network
The PCC is the electrical boundary point where the customer's generation system interconnects with the utility grid, and is the reference point for interconnection requirements.
Question 4: What document must be executed between a solar system owner and the utility before a grid-tied PV system can be legally energized?
- Certificate of Completion from the installer
- Interconnection Agreement (Correct answer)
- Net Metering Application
- Authority Having Jurisdiction (AHJ) Building Permit
Correct answer: Interconnection Agreement
An Interconnection Agreement is the legally binding contract between the customer and the utility governing the terms and conditions for connecting a distributed generation system to the grid.
Question 5: What is 'unintentional islanding' in the context of grid-tied solar PV systems?
- A PV system installed on a remote island with no grid access
- A condition where a PV system continues to energize a section of the utility grid after that section has been disconnected from the main grid (Correct answer)
- Intentional operation of a battery backup system during a grid outage
- An off-grid PV system operating independently of any utility
Correct answer: A condition where a PV system continues to energize a section of the utility grid after that section has been disconnected from the main grid
Unintentional islanding occurs when a PV system continues to power an isolated section of the grid after disconnection from the main utility, creating shock hazards for utility workers.
Question 6: Under IEEE 1547, what clearing time is required for a distributed energy resource when voltage drops below 50% of nominal voltage?
- 0.16 seconds (approximately 10 cycles) (Correct answer)
- 5 minutes
- 30 seconds
- 2 minutes
Correct answer: 0.16 seconds (approximately 10 cycles)
IEEE 1547 Table 1 specifies a clearing time of 0.16 seconds (approximately 10 cycles) for severe undervoltage conditions (V < 0.50 pu) to rapidly protect equipment and personnel.
Question 7: Which type of inverter is required for a grid-direct (no battery backup) solar PV system to legally export power to the utility grid?
- Stand-alone inverter with pure sine wave output
- Grid-tied synchronous inverter (Correct answer)
- Modified sine wave inverter with transfer switch
- Rotary phase converter
Correct answer: Grid-tied synchronous inverter
Grid-tied synchronous inverters lock onto the utility grid's frequency and voltage to safely synchronize power export, and include required protections like anti-islanding.
NABCEP Grid Interconnection 1
What is the primary standard that defines technical requirements for interconnecting distributed energy resources, including solar PV systems, to the electric power system?