Rick,
Table 22.1 and clause 22 of UL 746A talk about CTI. The CTI is a
voltage.
UL 746C, clause 11 talks more about CTI. Clause 11.2 states that the
comparative tracking voltage is an index and is not directly related
to the suitable operating voltage in actual service. Clause 11.3
states that the CTI provides an indication of the relative track
resistance of the material at voltages up to 600V.
Regards,
Frank Dominguez
______________________________ Reply Separator _________________________________
Subject: Comparative Tracking Index
Author: Non-HP-rbusche ([email protected]) at HP-Boise,mimegw150
List-Post: [email protected]
Date: 2/19/98 11:23 AM
IEC 950 defines CIT (comparative tracking index) in terms of
material groups for the determination of creapage distance. Specifically
groups I, II, IIIa and IIIb. are mentioned. In paragraph 2.9.3 (note 3)
the actual index (CTI) is referred to as <600 or <400. My questions are
as follows:
1. Is this CTI (as assigned by UL in the yellow book) actually a
voltage level?
2. The FR4 laminate we use has been rated at 205. As such the
maximum creapage distance is mandated. Is it common to find better
material? Is this 205 level typical of common FR4 materials?
Thanks
Rick Busche
Evans & Sutherland
[email protected]
