CODE CORNER: AHJs + Requirements vs. Allowances

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This NEMA 3R combiner box is rainproof, but not rain- or watertight. The weep hole allows water to drain from the box.
Label from a NEMA 3R combiner box shows it is rainproof, but not rain- or watertight.
This combiner box has multiple NEMA ratings, including 4X. Note the gasketed cover, which makes it rain/watertight.

This edition of “Code Corner” takes a look at the authority vested in local officials and building departments, the difference between requirements and allowances, and several examples where terminology is critically important to understanding Code requirements.

Who Makes the Call?

Section 90.4 in the National Electrical Code (NEC) stipulates that the authority having jurisdiction (AHJ) has the “responsibility for making interpretations of the rules, for deciding on the approval of equipment and materials...for granting the special permission contemplated in a number of the rules.” In general, AHJs rely on product standards created by national and international organizations and third-party testing to identify that equipment is “recognizable for the specific purpose, function, use, environment, application, and so forth.” Additionally, Section 90.7 states that, for listed equipment, “factory-installed internal wiring or the construction of equipment need not be inspected at the time of installation…”

Nationally recognized testing laboratories (NRTLs), such as Underwriters Laboratories (UL), Intertek ETL, TUV USA, and CSA, perform the applicable testing, and “list” manufacturer’s equipment to one or more standards, which literally means that the item “is included in a list published by an organization that is acceptable to the AHJ.” This inclusion means that the equipment “meets appropriate designated standards or has been tested and found suitable for a specified purpose.” If equipment is listed, that typically means it should be “labeled,” bearing a symbol or mark from an AHJ-accepted agency indicating adherence to appropriate standards.

Section 690.4(B) requires PV-specific equipment, including combiner boxes, modules, inverters, and charge controllers, to “be listed for the PV application.” Other equipment, such as wire, conduit, non-PV specific enclosures, and grounding electrodes, need to be listed for their application, but not specifically for use in PV systems. The AHJ will expect to see an NRTL label on all the gear that makes up the PV system.

Unlike “listed” and “labeled,” “marked” and “recognized” are not defined terms in the NEC, but are widely used throughout the NEC. For example, Section 690.17(A)(1) to (5) details manually operable disconnect types, requiring them to be “marked for use in PV systems.” This means that they are listed and labeled to an appropriate standard such as UL98B, “Outline of Investigation for Enclosed and Dead-Front Switches for Use in Photovoltaic Systems.”

The AHJ truly has the final call—in fact, the NEC defines “approved” as “acceptable to the AHJ—and further states in Section 110.2 that the “conductors and equipment required or permitted” in the NEC are “acceptable only if approved”! As such, the AHJ can grant “special permission” (Section 90.4) by written consent, so cultivating a good relationship with your local building department, plan reviewers, and inspectors—along with presenting a clear, documented rationale for your request—can go a long way.

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