The insulation materials used in positive-pressure electrical equipment are fundamentally the same as those in other types of explosion-proof electrical equipment. Consequently, the electrical clearance and creepage distances should also be identical.
However, for Class I electrical equipment, where the rated current exceeds 16A, such as in circuit breakers, contactors, or isolators, the possibility of arc generation during opening and closing necessitates that the insulation materials meet at least one of the following criteria:
1. A Comparative Tracking Index (CTI) not less than 400M, as stipulated in GB/T 4207-2012 “Methods for the Determination of the Comparative and Proof Tracking Indices of Solid Insulating Materials.” This level corresponds to material grades II or I.
2. The creepage distance between exposed live conductors of different potentials on the surface of the insulation material must comply with the requirements set forth in GB/T16935.1-2008 “Insulation Coordination for Equipment within Low-Voltage Systems – Part 1: Principles, Requirements, and Tests.” This standard applies to pollution degree 3: Class III overvoltage (refer to notes and Table 1.14 in Table 1.11).
