经受住的不同电压值规定了三个等级,
即:I级:CTI大于600V;II级:CTI在400到600之间;III级:CTI在175到400之间
标准原文请参考:
2.10.4.2 Material group and comparative tracking index
Material groups depend on the comparative tracking index (CTI) and are classified as follows:
Material Group I CTI ≥ 600
Material Group II 400 ≤ CTI < 600
Material Group IIIa 175 ≤ CTI < 400
Material Group IIIb 100 ≤ CTI < 175
The material group is verified by evaluation of the test data for the material according to
IEC 60112 using 50 drops of solution A.
If the material group is not known, Material Group IIIb shall be assumed.