Inspection and Approvals: Electrical Prefabrication

Published On
Apr 17, 2018

Construction methods have evolved from traditional ways of building and renovation to more efficient and cost-effective techniques. The construction industry now has the ability to model projects remotely and prefabricate many construction elements off-site. Prefab building components, which usually contain electrical wiring, are shipped to the site and set in place for application of building finishes, mechanical, plumbing and electrical connections to systems, and final testing or commissioning for acceptance and occupancy.

Prefabrication generally does not relieve the requirements for inspections and approval by the applicable authority having jurisdiction (AHJ). Compliance with codes and standards is still required, whether construction happens on-site or prefabrication is performed remote from the final installation. Electrical conformance assessment is evolving and includes prefabrication where construction efficiency is more a necessity and a requirement of owners and contractors.

Before getting into the basic methods of conformance assessment of electrical work—both built on-site and prefabricated remotely—it is important to recall how the North American electrical safety system functions. There are three essential elements of safe electrical installations. They are effective product safety standards and testing by qualified electrical testing laboratories, installation codes, specifically the National Electrical Code (NEC), and electrical inspections. These three elements of the safety system are essential for this system to function effectively. If any of the elements of the electrical safety system is eliminated, there is a risk and possibility of safety being compromised.

Section 110.2 of the NEC indicates that conductors and equipment are acceptable only if approved. Article 100 defines “approved” as “acceptable to the authority having jurisdiction.” Section 90.4 of the NEC indicates the AHJ is responsible for interpretations of the Code and for approvals. These are serious responsibilities to society and to building owners. In carrying out these responsibilities, the AHJs typically rely on use of listed electrical products and equipment and use this as a basis for issuing approvals as indicated in Section 90.7.

When an electrical product is listed, there is an assurance of conformance to applicable safety standards such as those developed by Qualified Electrical Testing Laboratories. Note that the Occupational Safety and Health Administration (OSHA) and, subsequently, AHJs recognizes several qualified electrical testing laboratories. If the electrical system is constructed on-site using listed electrical conductors and equipment, the inspector can just verify the installation conforms to the installation rules in the NEC and any installation instructions. If any of the equipment is not listed, it can complicate and often delay the approval process. Not all equipment addressed in the NEC is required to be listed.

Most electrical equipment, such as panelboards, conduit, wire and boxes, is listed. The listing process applies to manufacturers and typically includes some form of identification and labeling (usually listing or certification) from the testing laboratory that the product meets the applicable codes and standards. The field inspector then uses the certification or listing mark as a basis for product approval when installed on-site. Of course, the inspector still has to verify compliance when the listed parts are installed and connected to the building wiring system.

If we compare traditional built-in-place construction to prefabrication, we quickly see there has to be an effective method to verify Code compliance for building components that are fabricated in a facility remote from the final installation site. Especially if the fabrication involves concealing the electrical work, such as in prefabricated walls or ceilings. 

There are a couple ways to achieve conformance; one is if the fabricator is accredited by a qualified electrical testing laboratory and is conforming to all applicable product and installation standards for the fabricated components. This is not a requirement of the NEC.

A more common method of attaining AHJ approvals of prefabrication of electrical systems and building components is to arrange for inspections at the facility where the prefabricated building elements are constructed or assembled, specifically when the prefabrication involves concealment of electrical wiring. To effectively attain approvals, coordination is essential between the AHJ, the fabricator, electrical contractor, general contractor, and often the owner. 

In this case, the AHJ typically makes the inspections of the prefabrications at the facility and approves the prefabricated system. This is often done at an EC’s shop under controlled conditions. The approved prefabricated building components arrive on site and the inspector inspect the field connection of the prefabbed component to the building wiring system after it is set in place.

The electrical safety system requires an inspection process and to remain effective. Prefabrication must be coordinated with regard to the inspection and approval process. It is best to contact the AHJ proactively so all involved parties understand their roles, coordination is accomplished, and a safe Code-compliant electrical installation is achieved.

About the Author

Michael Johnston

Executive Director of Standards and Safety, NECA

Michael Johnston is NECA’s executive director of standards and safety. He is a member of the NEC Correlating Committee, NFPA Standards Council, IBEW, UL Electrical Council and NFPA’s Electrical Section. Reach him at

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