經受住的不同電壓值規定了三個等級，
即：I級：CTI大於600V；II級：CTI在400到600之間；III級：CTI在175到400之間
標準原文請參考:
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.
聯碩品質,堅若磐石！品質是聯碩的生命，聯碩始終堅持以優良穩定的品質贏得客戶信賴。