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Field Evaluations — Standards NFPA 790 and NFPA 791

When equipment is modified, rebuilt, or installed without a listing, a field evaluation will help determine if the product still meets safety requirements.

An electricalroom with circuit breakers.

September 11, 2020

Authored by: Jeffrey A. Fecteau, CBO, Senior Regulatory Engineer

The National Electrical Code® (NEC) requires equipment to be listed in numerous NEC Articles and gives further guidance for judging equipment in Section 110.3(A) and 110.3(C) for product testing, evaluation and listing (certification). The Occupational Safety and Health Administration (OSHA) requirements in 29 CFR 1910.303(a) include a general mandate that all electrical equipment in the workplace be “approved” by being “certified” or subjected to a complete and thorough evaluation before use. Additionally, many state, county and local electrical jurisdictions have incorporated similar requirements within their own laws, ordinances and rules.

However, sometimes equipment is installed that has not been certified (listed), has been modified or has been rebuilt. In these cases, a field evaluation may be necessary to determine that the product meets or continues to meet the applicable safety requirements mandated by the NEC. The need for a field evaluation is determined by the authority having jurisdiction (AHJ), who is responsible for final approval as to compliance with applicable codes and regulations. There are numerous local and national testing agencies that claim competency to conduct field evaluations of electrical equipment. In the absence of other evidence, National Fire Protection Association (NFPA) 790, Standard for Competency of Third-Party Evaluation Bodies (FEB), and 791, Recommended Practice and Procedures for Unlabeled Equipment Evaluation, provide guidance for how an AHJ can verify such competency claims.

Some testing organizations claim they are “recognized” to evaluate products in the field by virtue of their OSHA Nationally Recognized Testing Laboratory (NRTL) accreditation. However, OSHA does not evaluate an organization’s competency or credentials to field evaluate products.

The International Accreditation Service® (IAS) provides independent, third-party accreditation of field evaluation bodies (FEBs) using Accreditation Criteria for Field Evaluation of Unlisted Electrical Equipment (AC354). As part of the AC354 accreditation process, the FEB must demonstrate compliance with both NFPA 790 and NFPA 791. Additionally, AC354 states that all recommended practices and procedures in NFPA 791 are mandatory requirements to achieve IAS accreditation. The IAS FEB accreditation provides the AHJ with the independent, third-party validation needed to approve an FEB to perform field evaluations within their jurisdiction. UL maintains IAS FEB accreditation as FEB-107.

Some jurisdictions have their own FEB application and accreditation procedures, while others simply require field evaluations to only be conducted by NRTLs with accreditations for the specific equipment being evaluated. In either of these cases, both NFPA 790 and NFPA 791 offer recognized best practices for jurisdictions to determine competency of a field evaluation body as well as the minimum procedures for field evaluating electrical equipment.


NFPA 790, Standard for Competency of Third-Party Field Evaluation Bodies

NFPA 790 establishes minimum competency requirements for organizations that perform field evaluations. The standard requires that FEBs demonstrate technical expertise on the equipment being evaluated and apply requirements from applicable nationally recognized product safety standards when evaluating installed products. An FEB must be totally independent and is prohibited from having any conflicts of interests, such as being owned by or under control of manufacturers, suppliers or installers of equipment that it is evaluating. An FEB may not design or complete modifications required for a product to achieve compliance.

All personnel involved in the field evaluation process are required to meet technical competency criteria regarding any equipment they are evaluating. All FEBs must maintain records related to technical staff qualifications, training and experience, which are subject to audit.

A field evaluation may consist of a preliminary evaluation at a manufacturing location or other interim distribution facility, or at the location of the final installation. The process must always be completed with an evaluation of installed equipment at the final installation site. A copy of the FEB report, including any items needing corrective action, is provided to the AHJ at the conclusion of both preliminary and final evaluations. The format and content of the final report is defined in NFPA 791.


NFPA 791, Recommended Practice and Procedures for Unlabeled Electrical Equipment Evaluation

This document was developed to describe recommended field evaluation procedures for all FEBs. NFPA 791 is intended to drive consistent practices and application of requirements, all of which assist AHJs in making code compliance decisions.  Section 4.4 of NFPA 791 recommends the FEB notify the electrical AHJ in writing when initiating a field evaluation

A field evaluation may be conducted on either new or used equipment. Requirements for any field evaluation should be drawn principally from the applicable nationally recognized product safety consensus standard, such as those developed by Underwriters Laboratories.  A field evaluation determines that unlisted, altered or rebuilt equipment can be installed in a manner to achieve compliance with an adopted model code. Model codes, such as the NEC, provide installation requirements and are not intended to be used as a primary assessment standard for a proper field evaluation.

In accordance with the recommendation in NFPA 791, UL ensures the AHJ is notified in advance of any field evaluation to identify any concerns that the AHJ may have and to provide an AHJ the opportunity to be present during the final field evaluation.

When evaluating electrical equipment, a key requirement is that it must be capable of being installed in accordance with the NEC. This includes:

  • Verifying the presence and accuracy of complete equipment nameplate ratings and other required markings
  • Reviewing and determining compliance with manufacturer’s installation instructions
  • Assessing availability of adequate wire bending space and field wiring terminations
  • Determining the suitability of insulating and enclosure materials
  • Assessing corrosion protection and suitability of equipment for the environment where it’s being installed
  • Verifying proper grounding and bonding
  • Reviewing short circuit current ratings, overcurrent protection and disconnecting means

Because a field evaluation is completed outside of a testing laboratory and the need for the equipment to function properly and safely at the conclusion of the field testing, nondestructive electrical testing should approximate as closely as possible the testing required by all applicable standards. Such testing may include:

  • Insulation resistance
  • Leakage current and dielectric voltage withstand
  • Ground continuity
  • Input voltage and current at various design loads
  • Temperature rise for heat producing components
  • Safety interlock and emergency stop functions
  • Other testing as deemed necessary

All deficiencies are identified in a complete field evaluation report that is provided to the customer and the AHJ. Corrective actions may be taken to resolve such deficiencies, and when all issues are satisfactorily resolved, a field evaluated label is applied –– to the evaluated equipment at the final installation site. Only the FEB is authorized to apply the label.

UL has conducted field evaluations on approximately 80,000 pieces of electrical equipment over the past five years. Statistics generated from those field evaluations show that more than 65 percent of evaluations resulted in the identification of one or more safety issues requiring correction prior to issuing a field evaluation label. For more information on UL Field Evaluations, visit, or contact UL at [email protected] or by phone at 1.877.UL.HELPS, prompt number 2.

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