What is an NRTL?UL is an example of a product safety organization known generically as a Nationally Recognized Testing Laboratory (NRTL). NRTLs provide independent evaluation, testing, and certification of the safety of electrical products. The term NRTL and the requirements for recognition are established by the Occupational Safety and Health Act (OSHA) 29 CFR1910, which requires that all electrical equipment used in employee workplaces be NRTL-approved where such approval is available.
Other electrical testing agencies, such as ETL and MET Electrical Testing Co. are also recognized NRTLs. Since these organizations generally test products according to the applicable UL standards, our discussion will focus on those standards and terminology, but this is not intended as an endorsement of UL over any other testing agency.
The National Electrical Code (NEC) also requires that certain types of equipment such as light fixtures be NRTL-approved. There is no general requirement that all equipment be approved, but evidence of approval is recommended in Article 110 as a means of verifying the safety of appliances and equipment whose construction is otherwise outside the scope of the NEC. Some government jurisdictions, including my home state of Minnesota, require NRTL approval of all electrical equipment installed in facilities subject to their inspection authority.
Types of ApprovalUL provides several levels of product approval, which have important distinctions:
Listing, indicated by the familiar letters “UL Listed” inside a circle, indicates that the product has been approved for its intended use.
Component recognition, indicated by the letters “UR” written backwards, indicates that the product has been approved only for use as a component part of a UL-listed product or assembly, and not on a standalone basis.
Classification means that the product has been investigated only with respect to certain safety-related characteristics, such as flammability.
For electrical systems used with hvacr equipment, listing is the appropriate approval category to specify.
If a product is used in certain specific applications, such as explosive atmospheres, other approvals such as Factory Mutual (FM) or American Gas Association (AGA) may be acceptable or even preferred by the inspection authority. A good deal of equipment for these applications carry multiple agency approvals.
Beware of Control PanelsThe integral wiring and controls of standard manufactured products are investigated with the equipment and are covered by the listing of the product itself. In the case of separately provided control panels, or equipment for which no listing category exists, the controls must be separately evaluated. The standard normally applied is UL 508 — Industrial Control Equipment. This is an assembly standard, i.e. in addition to requiring that all components be approved, the standard addresses enclosure construction, wiring methods, overcurrent protection, and other aspects of how the components are applied and assembled in a control panel. This is an important distinction to watch out for in shop drawing review; simply using listed components inside a listed enclosure does not produce a listed control panel.
Distinction between compliance and listing is important. A manufacturer may claim to comply with a standard, and very well may. However, before an NRTL will allow a product to be labeled for compliance it will conduct an independent evaluation, and the manufacturer must agree to subject their manufacturing process to follow-up inspections to ensure that compliance is maintained. UL states clearly in its literature that the only evidence of UL compliance is the presence of the listing or recognition mark on the product.
Get it in the SpecTo obtain compliance with OSHA and reduce the risk of inspector rejections of electrical control panels, specifications should require that all electrical equipment, components, and assemblies be listed and labeled by a Nationally Recognized Testing Laboratory meeting the requirements of 29 CFR1910 where such listing is available.