Technological Innovation

What is UL 1621?

UL 1621 is a standardized test method developed by Underwriters Laboratories (UL), a global safety consulting and certification company. This test method evaluates the performance and reliability of electrical insulating materials used in various products, such as electrical appliances, electronics, and industrial equipment.

Understanding UL 1621 Testing Procedure

The UL 1621 testing procedure is designed to assess the ability of an insulating material to withstand electrical stress without breakdown or failure. The test involves subjecting the material to specific voltage levels under controlled conditions to evaluate its dielectric strength, endurance, and resistance to thermal degradation.

Dielectric Strength Evaluation

One important aspect of UL 1621 testing is assessing the dielectric strength of the insulating material. Dielectric strength refers to the maximum electric field intensity that an insulating material can withstand without experiencing electrical breakdown. During the test, the material is placed between two electrodes, and a steadily increasing voltage is applied until breakdown occurs. The voltage at which breakdown happens determines the dielectric strength of the material.

Endurance Testing

Endurance testing is another critical component of UL 1621 evaluation. This test aims to determine how well the insulating material performs under prolonged exposure to electrical stress. The material is subjected to a constant voltage for a specified period while monitoring any signs of degradation or failure, such as insulation breakdown, arcing, or changes in mechanical properties.

Thermal Degradation Resistance

UL 1621 also assesses the resistance of insulating materials against thermal degradation. In this test, the material is exposed to elevated temperatures to simulate real-world operating conditions. The objective is to ensure that the material can withstand the expected heat generated during normal use without losing its electrical insulation properties or becoming a fire hazard.

Importance of UL 1621 Certification

UL 1621 certification holds significant importance for manufacturers and consumers alike. For manufacturers, certifying their products according to this standard demonstrates compliance with industry regulations and builds trust among customers. It assures buyers that the product has undergone rigorous testing and meets the required safety standards.

For consumers, products bearing the UL 1621 certification mark provide peace of mind. It signifies that the product has been tested for safety and reliability, reducing the risk of electrical hazards or malfunctions. When purchasing electrical appliances or devices, it is crucial to look for UL certifications to ensure the highest level of product performance and safety.


UL 1621 plays a vital role in ensuring the quality and safety of electrical insulating materials used in various applications. The comprehensive testing procedure evaluates dielectric strength, endurance, and resistance to thermal degradation, providing manufacturers and consumers with confidence in the product's performance and longevity. When choosing electrical products, remember to look for the UL 1621 certification mark to make informed and safe choices.



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