By contrast, U.S. standards frequently call out specific construction features that will deliver the appropriate performance. You get a safe installation either way, but the difference in philosophy affects both content and compliance. Traditionally, in the U.S. we guarantee a certain conductivity for copper, then sell conductors by weight. If you buy the right weight, it will carry the current you want. With the IEC philosophy, you re guaranteed a maximum total resistance in your cable.
Weight is irrelevant.
IEC compliance is different too. In the U.S., products go to a third-party testing agency such as UL for certification. In IEC practice, the manufacturer performs three types of tests and certifies the results. The manufacturer does type testing to prove the design. After that, routine tests are conducted at the factory.