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Non metallic material shell: ball pressure test, hot wire test, needle flame test, UL and IEC differences

April 5, 2024

In the IEC standard, ball pressure test, Glow wire test, and needle flame test are three main tests used to determine the qualification of plastic materials in products. The main difference between UL and IEC when reviewing non-metallic materials is:


1. Ball pressure test and oven test: IEC ball pressure test is a test that determines the softening degree of a material by placing a ball pressure device on the material and baking it in an oven for one hour. UL oven testing is a test for finished products that uses a 7-hour oven to determine whether the outer shell components will crack or deform as a result.


2. Required flammability level: IEC 60335 requires that all non-metallic materials that may be ignited or spread flames should undergo a hot wire test at least 550 ℃ or have an HB40 rating. When the flammability rating of the material cannot be confirmed, and when needle flame testing is not used, the IEC standard requires components close to or supporting current carrying connectors to undergo hot wire testing at higher temperatures. For UL standards, the requirements for the flammability level of the casing depend on the usage of the product. For example, portable products working under human supervision should have a shell material of at least HB grade, while portable products working under unmanned supervision require a material of at least V-2 grade. HB grade materials allow a combustion rate of 80mm per minute when the thickness is less than 3mm, while HB40 requires a combustion rate of less than 40mm per minute. Both HB40 and HB grades of materials allow a combustion rate of 40mm per minute when the thickness is greater than 3mm.


3. Hot wire test and hot wire ignition test (HWI): UL hot wire ignition test is a material test, while IEC hot wire test is a finished product test. UL 746C allows the use of a hot wire test as an alternative to determining the HWI requirements for materials.


4. Direct contact with live parts or supporting current carrying connectors: UL 746C includes requirements for direct contact or close proximity to non insulated live parts, mainly including determining whether the material has the required HAI, HWI, and CTI. As mentioned earlier, HAI and HWI depend on the flammability level of the material. For IEC, components that support or are close to current carrying connectors need to undergo further hot wire testing and evaluation. The temperature of the hot wire depends on the usage of the finished product and the current carrying capacity of the connecting components. The IEC hot wire test can also reference UL's hot wire ignition temperature (GWIT) and hot wire combustion index (GWFI).


5. Close proximity: According to UL746C, this term applies to components within 0.8mm of non insulated live parts. For IEC, it is applicable to components within 3mm of the supporting current carrying connector.