Most wire and cable specifications are preceded by designations such as ZR, ZA, ZB, and ZC, representing different flame retardancy levels. So, what exactly are the flame retardancy ratings for wires and cables, and how are they classified?
ZR stands for flame retardancy, which is further divided into three levels: A, B, and C. If a wire or cable is marked with ZB before its model number, it is classified as Class B flame retardant; if not specifically marked, it is assumed to be Class C flame retardant. In terms of flame retardancy, ZA is the highest, ZB is the second, and ZC is the lowest. Whether it's wire used for home decoration or power cables, differences in flame retardancy levels directly impact safety and performance standards.
ZA, ZB, and ZC Classification
The ABC classification of flame-retardant cables is based on the GB/T18380-2008 standard and is designed to evaluate the flame suppression capabilities of vertically mounted bundled wires, cables, or optical cables under specific conditions.
Test Standards for Each Grade
The test conditions for flame-retardant Class A cables are as follows: The cable is installed on a test ladder, ensuring that the total volume of non-metallic material is 7 L/m. After 40 minutes of burning, the cable must be dried and the specimen must be cleaned. The maximum charring range must be within 2.5 meters of the base of the blowtorch.
The test for flame-retardant Class B cables is slightly different: the cable is also installed on a test ladder, but the total volume of non-metallic material is reduced to 3.5 L/m, and the burning time remains 40 minutes. After the burning stops and the specimen is dried, the charring range must also not exceed 2.5 meters from the base of the blowtorch.
For flame-retardant Class C cables, the test is more streamlined: when installed on a test ladder, the non-metallic material volume is reduced to 1.5 L/m, and the burning time is shortened to 20 minutes. After the burning ends, the maximum charring range of the specimen must also be within 2.5 meters from the base of the blowtorch.
