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Comparative Tracking Index (CTI) - UL 746

The voltage which causes tracking after 50 drops of 0.1% ammonium chloride solution have fallen on the material. The results of testing at 3 mm thickness are considered representative of the material's performance in any thickness.

Tracking is an electrical breakdown on the surface of an insulating material. A large voltage difference gradually creates a conductive leakage path across the surface of the material by forming a carbonized track.

Performance Level Categories (PLC) were introduced to avoid excessive implied precision and bias.

Tracking Index (V) PLC
600 and Greater 0
400 through 599 1
250 through 399 2
175 through 249 3
100 through 174 4
<100 5

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