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Let’s Talk About Obtaining NRTL Approvals More Effectively

Most markets of electrical/electronic devices require some form of third-party safety agency certification of the products before they can be sold into that market. In North America, this involves working with a third-party safety certification agency, also known as a Nationally Recognized Testing Laboratory (NRTL), the entity that verifies the product complies with the applicable UL/CSA safety standards.

Working with a NRTL such as UL or CSA can be very challenging and frustrating. The usual experience when working with a NRTL is that projects are, more often than not, late, costs are overrun, and certification reports often inaccurate. This is not always the fault of the NRTL.

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For most electrical/electronic products, the NRTL certification logo must be printed on NRTL approved labels and the label must be placed on the products before they can be installed at a customer’s premises, installed into customer racks or panels and later powered on for official use by the customer. The NRTL logo on the product confirms it has been evaluated by a NRTL and complies with all applicable product safety standards. Due to OSHA, other safety regulations, and customer requirements, there is usually no way to bypass the NRTL third-party certification process and involvement of a NRTL in electrical/electronic development is nearly necessary.

Third-party Product Safety Certification Approval Process

A NRTL certification process is a lengthy 5-step process culminating in either a “Findings Report” for products that do not comply or a “Certification Report” for products that do comply. The Certification Report is used during factory inspections to verify that the product continues to be manufactured as originally certified.

The 5-Step Certification Project Process is as follows:

Step 1: Construction Review

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The assigned NRTL engineer reviews the physical design of the product to determine its compliance with the applicable safety standards and inspects samples of the product while verifying and documenting compliance. They will confirm spacings (creepage and clearance distances), review the instruction manual, and all markings and labels. This is a time-consuming process and the report is hundreds of pages in length. As part of their investigation, the NRTL will review schematics, block diagrams, unvarnished (or un-potted) samples of transformers, adequacy of dimensions/spacings on actual samples, adequacy of safety critical components such as fuses, Y-capacitors, X-capacitors, opto-couplers, terminal blocks, the enclosure and other product markings. The safety instructions required by the standards must be included in the instruction manual and the NRTL will also review this information as part of the certification efforts.

During their investigation, the NRTL is looking for any issue that would jeopardize protection against electric shock or protection against mechanical hazards.

They look for resistance to mechanical stresses, protection against the spread of fire, equipment temperature limits and resistance to heat, protection against hazards from fluids, protection against radiation, including laser sources, and against sonic and ultrasonic pressure. Finally, they look for protection against liberated gases and substances, explosion and implosion if applicable to the product.

Step 2: Testing

The worst-case product configuration/loading is selected for testing. The purpose of testing is to confirm that safety hazards do not exist during normal operation and single fault conditions. A test plan guides the NRTL in selecting test conditions and test parameters for each test and each product variation to be tested. When prototypes are available, several samples of the product must be sent to the NRTL or the NRTL must visit the manufacturer to conduct a safety investigation and perform testing. The NRTL will conduct many tests on the product including: temperature, humidity, dielectric strength, impulse, ingress protection, overload, breakdown of components, transformer abnormal operation, ground continuity, impact – just to name a few!

Step 3: Project Reports

Based on results of the construction review and testing one of two different reports may be generated by the NRTL.

Findings Report

If it is determined the product is non-compliant in construction features or tests results, the NRTL engineer provides a Findings Report that summarizes their concerns. The NRTL engineer working on the project is usually not allowed to provide solutions to correct any non-compliances, they may however provide suggestions for bringing the product into compliance. If a Findings Report is received, expect an extension of the project timeline and an increase in fees associated with re-evaluation of corrected product.

Certification Report

If all goes well and the product is found to comply during the construction review and testing, the NRTL engineer drafts a Certification Report instead of a Findings Report. The Certification Report controls the elements of the product that are critical to bringing the product into compliance with the safety standards. Items that are considered critical include safety critical components (i.e. items that provide isolation), dimensions, materials, safety instructions, and required markings. Pictures and illustration are included in the report. Manufacturers use this report to guarantee they continue to produce a product that complies with the safety standards.

Step 4: Project Review

A second NRTL engineer reviews the draft Certification Report produced by the original NRTL engineer assigned to the project. The second NRTL engineer must agree with the first engineer’s conclusions that the product complies with the safety standards and the product was tested adequately. Very often, the reviewing engineer finds discrepancies which affect the Certification Report and which the first engineer must correct before certification is granted. Sometimes this finding negatively impacts the manufacturer, especially if additional testing is deemed necessary or a component is found non-compliant with the safety standards late in the product development cycle.

Step 5: Report Issued

After review and approval by a second NRTL engineer, the NRTL issues the Certification Report.

The manufacturer must verify this report is accurate prior to project closure otherwise they could receive a variation notice (i.e. non-compliance finding) during one of the unscheduled quarterly factory audits that are performed by the NRTL. It is during these audits where the NRTL reviews the report issued against the product produced to ensure the manufacturer is continuing to produce a product as described in the report and which complies with the safety standard.

Product Complexity

Complicating the product safety certification process is that many electrical/electronic products have many different configurations available, several of which have circuits that are considered hazardous from a safety perspective because of the voltages, currents, and/or energies involved. This variety and complexity confuses the NRTL and it makes their job much more difficult. With the manufacturer’s help, the NRTL must determine worst case configuration for testing and this often involves some experimentation resulting in extra time and money over what is typically required for much simpler products.

Historical NRTL Issues

Some of the issues the author has experienced during product safety certifications include:

  • NRTL engineer lacked experience and overlooked some requirements.
  • NRTL didn’t understand full scope of project prior to quoting.
  • Tests not performed correctly and retesting was required.
  • NRTL requested additional scope not originally agreed upon during project planning resulting in further delays and increased costs.
  • Issues with safety-critical components identified too late in the project.
  • Uncoordinated findings provided throughout the review.
  • Inconsistent instruction manual safety information provided.

What Manufacturers Can Do to Make Third-Party Safety Certification Go Easier?

Projects that do not involve long-term testing can be completed within an 8 to 12-week time-frame, however the author has experienced the time required is much longer with some NRTLs.

Here are some tips that have proved helpful in obtaining NRTL approval more effectively:

  • Generate a critical component list early in the product development process and verify these components comply with relevant UL/CSA/IEC standards. Obtain third-party issued IEC CB Certificates, UL/CSA File numbers, and datasheets for these safety critical components.
  • Consider having the NRTL conduct a preliminary investigation of the design, especially if involves a new product concept or unique design.
  • Don’t wait for perfect samples to start testing.
  • Consider breaking up one big project into smaller ones so the scope of the smaller projects is much easier for the NRTL to understand and manage.
  • Provide correct/detailed insulation diagrams at launch of the NRTL evaluation.
  • Read the applicable standard and know it as well as or better than the NRTL engineers.
  • Design the product to comply with the standard from product inception.


Working with a NRTL to obtain product safety certification is often a laborious process that often results in cost increases and product shipment delays. With slight changes to how manufacturers go about it, many of these troublesome issues can be avoided, costs will decline, and product shipment deadlines will be met.


  1. CertifGroup, Understanding the UL – CSA Certification Process

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