CQD Spotlight features questions and answers from NECA and ELECTRICAL CONTRACTOR’s Code Question of the Day program. Whether you’re a seasoned contractor, an apprentice or simply a National Electrical Code enthusiast, you’ll gain knowledge with a nod to the legacy of Charles M. “Charlie” Trout, a true NEC legend.

From the archives—Dec. 20, 2024

I am reviewing a set of installation instructions for a listed photovoltaic (PV) hazard control system for a roof-mounted 9-kW PV system. Two questions: what is a PV hazard control system, and what product standard covers the listing of these systems?

The purpose of a PV hazard control system is to perform functions that reduce the risk of electric shock within a damaged PV array for firefighters. The idea is to provide protection for firefighters from accidental contact. For example, a firefighter is running, then trips and falls and punctures the PV module with their axe. UL 3741, Photovoltaic Hazard Control Standard, is the product standard from UL for these systems.

Here are some definitions from UL 3741:

PV hazard control equipment: A complete piece of equipment evaluated for compliance with UL 3741 that performs function(s) related to reduction of electric shock hazards for firefighters performing their work in the vicinity of the PV array.

PV hazard control system: System of one or more PV hazard control equipment and other specific or generic specified PV array equipment that has been evaluated to comply with the system requirements of UL 3741 when installed in accordance with the manufacturer’s installation instructions.

From the archives—Aug. 1, 2024

We are wiring a utility-interactive PV inverter containing built-in output overcurrent protection. The output conductors terminate in a nonfused disconnect prior to terminating in the utility transformer. Should there be overcurrent protection at the disconnect?

In general, Section 240.21 requires the OCPD to be located where the conductors receive their supply. In the installation described in the question, this would be the disconnect. Section 705.30 requires the conductors for interconnected electric power production sources to be protected in accordance with Article 240.

From the archives—Dec. 17, 2024

I was recently red-tagged for not having a plainly visible nameplate for an exterior residential energy storage system installation. The ESS unit information was located under the NEMA 3R enclosure cover. Does the code require the information to be on the exterior of the enclosure, and not behind the cover?

The charging text in Section 706.4 requires the information listed in 706.4(1)–(8) to be marked with a nameplate that is plainly visible after installation. The term “plainly visible” is not defined by the NEC. The NEC Style Manual governs the way the code is written and structured. However, there is an additional document that generally governs how all NFPA documents, including the NEC, are written and structured: the NFPA Manual of Style for Technical Committee Documents. Per Section 3.2.1.2 of this guide, the spelling of general words or terms shall follow Webster’s Collegiate Dictionary, 10th edition. Webster’s defines “plainly” as “free of impediments to view or unobstructed.” Based on that definition, any marking behind the cover of an enclosure that can only be seen after removing the cover would not be plainly visible.

From the archives—July 30, 2024

We have a PV system installed on a detached garage supplied by a 30A, 3-wire feeder. As such, the grounded conductor is bonded to the grounding electrode system (ground rod) at the garage. The PV system output is greater than the garage feeder conductors are rated for, so the PV grid-tie conductors were run back to the main structure’s electrical panel. The PV inverter is connected to the grounding electrode system of the detached garage. Since the garage has only a 3-wire system, we decided to isolate the grounded conductor from the equipment grounding conductor (EGC) and grounding electrode system to avoid a parallel path. There is an EGC run with the PV grid-tie conductors back to the service panel in the main structure, so we upsized the EGC to accommodate the PV system and garage feeder. Is this legal?

This would not be permitted, as Section 250.118 requires the equipment grounding conductor to be run with or enclosing the circuit conductors except for certain conditions outlined in sections 250.130(C) and 250.134(A), Exception No. 2. Neither of these sections apply to this installation.

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