NRTL (Nationally Recognized Testing Laboratory) certification is a program operated by the U.S. Occupational Safety and Health Administration (OSHA) that verifies products comply with U.S. workplace safety standards. This program is defined under 29 CFR Part 1910.7, and OSHA-recognized NRTLs conduct product safety evaluations within their accredited scope.

NRTL certification covers a wide range of products, primarily electrical and electronic equipment. While the primary focus is on safety, evaluations also extend to aspects directly linked to safety such as product performance, construction, labeling, and quality management systems.

Products certified by an OSHA-recognized NRTL may bear the NRTL mark. This mark not only enhances trust and reliability in U.S. distribution channels but also directly contributes to preventing workplace accidents.

In 2025, JET obtained recognition from OSHA as an NRTL. Our current accreditation scope is as follows (*):

• Recognized Testing Standards
  UL 1741 Inverters, Converters, Controllers and Interconnection System Equipment for Use With Distributed Energy Resources
• Recognized Testing Sites
  
  • Tokyo Site: Factory inspections
  • Koriyama Site: Product certification testing using large-scale facilities (up to 5 MW capacity)
  (*) Details of the accredited scope are available on the official OSHA website: (OSHA NRTL Program - JET)

The accredited scope will be expanded in the future according to customer requests.

UL 1741 is a safety standard applied to inverters, converters, controllers, and interconnection equipment—including Power Conditioning Systems (PCS)—used to connect distributed energy resources such as photovoltaic (PV) systems and battery energy storage systems to the grid.

The requirement for PCS to comply with UL1741 arises from the following two regulatory drivers:

• OSHA Workplace Safety Regulations
  To ensure workplace safety under federal law, OSHA requires NRTL certification for many electrical and electronic products. UL1741 is one of the covered standards, and PCS must obtain certification to confirm safe workplace use.
• Utility and ISO Interconnection Requirements
  U.S. utilities and Independent System Operators (ISOs) reference UL1741 as a technical requirement to ensure smooth grid interconnection of distributed energy resources. For example, compliance with UL1741 is mandated under California’s Rule 21, Hawaii’s Rule 14H, and the New York ISO (NYISO) interconnection requirements.

Thus, UL1741 is indispensable both from the perspective of workplace safety (OSHA regulations) and grid interconnection (utility/ISO requirements). Certification is effectively mandatory for PCS manufacturers entering the U.S. market.

Representative test categories under UL 1741 (3rd Edition / Supplement B) are as follows:

• General Safety / Construction
  - Design requirements for enclosure safety and accessibility
  - Electrical safety: protection against electric shock, insulation verification
  - Mechanical safety: enclosure structure, strength evaluation
  - Environmental durability: resistance to temperature, humidity, and corrosion
• Grid Interconnection Tests (Referencing IEEE 1547 Requirements)
  UL1741 tests reference the interconnection requirements defined in IEEE 1547, and certification confirms compliance with these requirements.
  - Output characteristics: rated power, efficiency, waveform quality
  - Protection functions: response to overvoltage, overcurrent, frequency deviation
  - Grid support functions: voltage and frequency support as defined in IEEE 1547
  - Power quality: harmonic distortion, flicker, output fluctuations
• Durability and Reliability Tests
  - Long-term operation and stress testing
  - Verification of component lifetime and degradation behavior
• Marking Requirements
  - Compliance of product labels (ratings, warnings, etc.)

Obtaining NRTL certification involves more than passing product testing—it also requires evaluation of the manufacturer’s quality management system and ongoing follow-up services after certification.

Through this process:
- Compliance of the product with safety standards
- Consistency of quality in mass production
are both verified by an independent third-party body. This ensures reliability and smooth distribution in the U.S. market.

The certification process consists of the following steps:

• Application acceptance: application for each product type is received
• Application review: documentation is checked, quotations issued as needed
• Contract signing: formal certification contract concluded
• Certification testing: evaluation of safety, performance, and protective functions
• Factory inspection: initial and periodic audits of quality management systems
• Certification evaluation: comprehensive review of testing and inspection results
• Certification approval: decision on certification and issuance of certificate/mark usage
• Certification registration: publication of certified products in databases and JET website

After certification, FUS (Follow-Up Services) are conducted, including ongoing factory inspections and market surveillance, to ensure continued compliance.

Products that have obtained NRTL certification may display the certification mark designated by the respective NRTL. This mark indicates conformity to applicable safety standards and is a prerequisite for product sales and distribution in the U.S. market.

In addition to displaying the certification mark alone, it is common practice to affix a certification label that incorporates the registered mark together with product-specific information such as ratings and applicable standard names. This ensures both traceability and reliability.

Applications and inquiries regarding NRTL certification services are accepted through the following channels. Please feel free to contact us for consultation, quotations, or schedule confirmation.