CTI is short for Comparative Tracking Index, means the maximum voltage measured in volts to verify the electrical breakdown properties of an insulating material that used in the electronic devices. At this voltage the specific material can withstands 50 drops of contaminated water without any tracking. Tracking means the conductive paths formed due to heat, electrical tress, humidity and contamination.

Normally, the CTI specified by IEC 60112 in below according to the result of the test method on the specific material.

Insulating material group               CTI
I                                                         600 ≤ CTI           (Shengyi S1600, KB-6160C)
II                                                        400 ≤ CTI < 600
IIIa                                                     175 ≤ CTI < 400 (KB-6160F CTI 175V LOW CTE UV-blocking; KB-6160 CIT 175V UV-blocking; KB-6160A CIT 175V UV-blocking)
IIIb                                                     100 ≤ CTI < 175 (Most FR1 base material can meet this value)

In printed circuit board, if you need a special CTI value for your electronic devices, a specified CTI value and it’s base material need to be selected before starting your design.