A Nationally Recognized Testing Laboratory (NRTL) is a certified third party capable of performing various inspections in the United States. Field evaluation services including Listing, Labeling and National Electrical Code inspections are among those offered by NRTLs such as TÜV SÜD America.
Listing and Labeling
In the United States, Authorities Having Jurisdiction (AHJ) are responsible for approving equipment, equipment installation and procedures. Equipment, services or materials are defined as being "listed" if they are subject to periodic inspections and evaluations that ensure local safety requirements are met, and that the equipment is used for its intended purpose. Such lists are published by organizations approved by OSHA and recognized by the AHJs and should be reviewed periodically.
Field Labeling is a method used to illustrate that unlisted equipment, previously used equipment, or equipment that has been relocated, meets local AHJ safety requirements. Third parties such as TÜV SÜD America are able to perform safety inspections of such equipment. Once a piece of equipment has been inspected, the third party agency affixes their field label to it, demonstrating to electrical inspectors that the equipment meets local requirements.
National Electrical Code
The NEC is a set of minimum requirements for safety of wiring and electrical installations. As per article 90 of the NEC, the purpose of this code is the practical safeguarding of persons and property from hazards arising from the use of electricity. The requirements in this code address the fundamental principles of protection for safety contained in Section 131 of International Electrotechnical Commission Standard 60364-1, Electrical Installations of Buildings. The code covers the installation of electrical conductors, electric equipment, signaling and communications conductors and equipment, and fiber optic cables and raceways for the following:
- Public and private premises, including buildings, structures, mobile homes, recreational vehicles, and floating buildings
- Yards, lots, parking lots, carnivals, and industrial substations
- Installations of conductors and equipment that connect to the supply of electricity
- Installations used by the electric utility, such as office buildings, warehouses, garages, machine shops, and recreational buildings, that are not an integral part of a generating plant, substation, or control center
NEC 90.7. Examination of Equipment for Safety
For specific items of equipment and materials referred to in this code, examinations for safety made under standard conditions will provide a basis for approval where the record is made generally available through promulgation by organizations properly equipped and qualified for experimental testing, inspections of the run of goods at factories, and service-value determination through field inspections. This avoids the necessity for repetition of examinations by different examiners, frequently with inadequate facilities for such work, and the confusion that would result from conflicting reports as to the suitability of devices and materials examined for a given purpose.
It is the intent of this code that factory-installed internal wiring or the construction of equipment need not be inspected at the time of installation of the equipment, except to detect alterations or damage, if the equipment has been listed by a qualified electrical testing laboratory that is recognized as having the facilities described above, and that requires suitability for installation in accordance with this code.
The conductors and equipment required or permitted by this code shall be acceptable only if approved.
FPN: See Examination of Equipment for Safety, Section 90.7, and Examination, Identification, Installation, and Use of Equipment, Section 110.3. See definitions of Approved, Identified, Labeled, and Listed.
Examination, Identification, Installation, and Use of Equipment
(a) Examination. In judging equipment, considerations such as the following shall be evaluated:
1. Suitability for installation and use in conformity with the provisions of this code
FPN: Suitability of equipment use may be identified by a description marked on or provided with a product to identify the suitability of the product for a specific purpose, environment, or application. Suitability of equipment may be evidenced by listing or labeling.
2. Mechanical strength and durability, including for parts designed to enclose and protect other equipment, the adequacy of the protection thus provided
3. Wire-bending and connection space
4. Electrical insulation
5. Heating effects under normal conditions of use, and also under abnormal conditions likely to arise in service
6. Arcing effects
7. Classification by type, size, voltage, current capacity, and specific use
8. Other factors that contribute to the practical safeguarding of persons using or likely to come in contact, with the equipment
(b) Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.
Articles 90.7, 100.2 and 110.3 of the 2002 National Electrical Code outlines considerations for approval of equipment by the AHJ. They imply that equipment should be evaluated to specific parameters by an organization with proper facilities to evaluate the construction and components of the equipment. Without third-party evaluated equipment, a jurisdiction would have to judge equipment based on NEC requirements alone. However, NEC requirements primarily focus on the installation of equipment and therefore, are not suitable for the evaluation of internal wiring and components used in many products. As an example, article 310 of the NEC cannot be used to evaluate the internal wiring of a complex modern machine, as it specifically relates to general wiring practices. Hence, the AHJ will need to verify that the equipment complies with the construction and performance requirements in the applicable standard, for which he/she has not been trained. Consequently, AHJ mostly rely on approved test labs (NRTLs such as TÜV SÜD America) to evaluate the suitability of equipment.
The Occupational Safety and Health Administration, or OSHA, develops and enforces standards pertaining to workplace safety in the United States. OSHA requires that certain types of equipment and materials be approved by an NRTL, organizations that are recognized by OSHA as meeting specified legal requirements.