Master Electrician Exam (NEC)Special Occupancies, Equipment, and ConditionsMedium
A master electrician is planning the electrical installation for a new solar photovoltaic (PV) system on a commercial rooftop. The system includes PV modules, an inverter, and a DC combiner box. Which of the following statements regarding the PV system's disconnecting means is correct according to NEC Article 690?
- AThe AC disconnecting means for the PV system must be sized for 100% of the maximum continuous current.
- BThe DC disconnecting means must be located within 10 feet of the PV array and visible from the array.
- CA readily accessible AC disconnecting means and a readily accessible DC disconnecting means are required for the PV system.
- DA single disconnecting means is required for the entire PV system, located at the service entrance.
Show answer & explanationAnswer & explanation
Correct answer: C. A readily accessible AC disconnecting means and a readily accessible DC disconnecting means are required for the PV system.
NEC 690.13 and 690.14 require both an AC disconnecting means and a DC disconnecting means for PV systems. Both must be readily accessible. The AC disconnect connects the PV system to the premises wiring, and the DC disconnect isolates the PV array from the inverter.
Why the other options are wrong
- A. The AC disconnecting means must be rated for at least 125% of the maximum continuous current from the inverter, similar to other continuous loads, not 100% (690.8(B)(1)).
- B. While proximity to the array is important for the DC disconnect, the 'within 10 feet' rule is not universally applied, and 'visible from the array' is often a goal, but 'readily accessible' is the primary NEC term. More importantly, the AC disconnect is also required.
- D. Multiple disconnecting means (AC and DC) are required, and their locations are specific, not just a single one at the service entrance.
PV System Disconnects (NEC)
Solar photovoltaic (PV) systems require both AC and DC disconnecting means, readily accessible, to safely isolate the PV array, inverter, and the connection to the premises wiring for maintenance and emergency shutdown.
- Requires separate AC and DC disconnects.
- Both must be readily accessible.
- AC disconnect isolates from utility/premises wiring.
- DC disconnect isolates the array from the inverter.
Memory trick: Solar Power: AC and DC, each needs its own cut-off switch, easy to reach.