Comparative Tracking Index
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 rbus...@es.com
Re: Comparative Tracking Index
Rick, The Comparitive Tracking Index (CTI), ASTM D3638 and UL746A, is a test intended to show the susceptibility to surface tracking of solid electrical insulating materials when exposed under electrical stress, to a contaminant solution.This test applies to relatively low voltages under 600 volts. The CTI test attempts to cause a permanent electrically conductive carbon path along the surface of a material using an aluminum chloride electrolyte applied at the rate of 1 drop every 30 seconds to the test specimen. The surface of the specimen is subjected to an AC voltage, s.c. current limited to one amp. The current flow must exceed 100 mA for at least a half second to register as an established path. ANSWER TO 1) The CTI level (205 in your note) is the voltage level that corresponds to 50 drops on the tracking-voltage curve that is plotted as a result of testing multiple 3.0mm thick samples at various voltage levels, up to600 V. ANSWER to 2) UL has CTI index levels, while international standards call out the actual voltage levels. Either way 200 volts is an probably an OK level for the material and what you will be using it for. I believe levels anywhere from 100 to 250 volts are typically called out for that use. Just my humble opinion, though. Any other questions, I have a bit of experience on this subject, please do not hesitate to e-mail me. Regards, Bob Tims Standards and Compliance rt...@emx.ericsson.se
RE: Comparative Tracking Index
But would you be surprised to know that UL doesn't retest a laminate's CTI after processing? They don't, unless specifically asked by the board mfg., which I'd have to suggest is rare. The CTI for finished boards in UL's RCD is based on those for the base laminate and no assumption should be made to the contrary. If a board house claims otherwise, ask them to provide the test data. Regards, Peter L. Tarver Nortel ptar...@nt.com > -- > From: Harold Leipold[SMTP:harold_leip...@sec.siemens.com] > Sent: Friday, February 20, 1998 6:04 AM > > > Just to add my "2 cents" to this discussion. CTI etc. after > manufactured > into a finished PCB is actually more important than the CTI of the > basic > laminate itself. That is one reason why one should use PCB vendors who > have > their process UL recognized (and use the recognized logo on the > finished > product for identification). > The PCB fabrication process, solder mask, etc. can affect both CTI and > flammability greatly. > > Comments are personal and do not necessarily reflect corporate > opinion. > > Harold Leipold > Siemens EC > Princeton, IN > Tel 812-386-2161 > Fax 812-386-2616
RE: Comparative Tracking Index
Rick, In past years I spent significant time researching this question. I also found that most materials manufacturers do not understand CTI. Even though the concept has been known for more than 50 years. As far as standards go I put this table together simply to help correlate the International, European and UL standards: VOLTAGE UL 746IEC 112 VDE 303 600 or greater 0II 400 - 599 1II II 250 - 399 2IIIa IIIa 175 - 249 3IIIa IIIa 100 - 174 4IIIb III b 0 - 99 5n/a n/a (If the columns do not line up, use tabs to delimit) If you have the UL yellow Recognized Component directory, you should be able to find the UL CTI info at the beginning of the plastics section. It is on page 1893 in my 1994 version. The 205 figure that you mention does not look like a CTI number, rather a thermal performance number. FR-4 "typically" is greater than 180C in thermal performance and the flame rating is UL 94V-0. CTI is a function of the organic content of the material, material that is able to be carbonized. For example anorganic materials such as glass and ceramics always have the highest possible CTI ratings and essentially do not track. If you will note, when using FR-4 for PCB's most standards including IEC950 and EN 60950 make a special case and provide a separate spacing table. The creepage numbers generally correlate directly to equivalent CTI of 600V. If you are using the FR-4 for something other than PCB's you will need to get exact information from the laminate manufacturer. Try to get past the sales people and you may still need to educate technical types as to what CTI is before you can get meaningful information. Chances are most all FR-4 laminates are CTI 600V, depending on glass content.. Doug Powell Advanced Energy Industries, Inc. Fort Collins, Colorado USA -- From: Rick Busche To: emc-p...@ieee.org Subject: Comparative Tracking Index List-Post: emc-pstc@listserv.ieee.org Date: Thursday, February 19, 1998 8:26PM IEC 950 defines CTI (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 rbus...@es.com
RE: Comparative Tracking Index
Rick, UL defines CTI as "the voltage which causes tracking after 50 drops of 0.1 percent ammonium chloride solution have fallen on the material. The results of testing the nominal 3mm thickness are considered representative of the material's performance in any thickness." Thanks SGour -Original Message- From: Rick Busche [SMTP:rbus...@es.com] Sent: Thursday, February 19, 1998 12:23 PM To: emc-p...@ieee.org Subject: Comparative Tracking Index 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 rbus...@es.com
Re: Comparative Tracking Index
Just to add my "2 cents" to this discussion. CTI etc. after manufactured into a finished PCB is actually more important than the CTI of the basic laminate itself. That is one reason why one should use PCB vendors who have their process UL recognized (and use the recognized logo on the finished product for identification). The PCB fabrication process, solder mask, etc. can affect both CTI and flammability greatly. Comments are personal and do not necessarily reflect corporate opinion. Harold Leipold Siemens EC Princeton, IN Tel 812-386-2161 Fax 812-386-2616 ri...@sdd.hp.com on 02/19/98 02:48:17 PM Please respond to ri...@sdd.hp.com To: rbus...@es.com cc: emc-p...@ieee.org (bcc: Harold Leipold/PRI/SEC/US) Subject: Re: Comparative Tracking Index Hi Rick: You ask about CTI for printed wiring boards, and typical values. According to the UL Yellow Book, CTI is indicated in volts. In glancing through the UL Yellow Book, very few board manufacturers have submitted their boards for CTI. The few that have submitted, have CTIs in the range of less than 100 up to about 250. A very few manufacturers can provide boards with CTI exceeding 600. Best regards, Rich "Life is ours to be spent, not to be saved." -- D. H. Lawrence - Richard Nute Quality Department Hewlett-Packard Company Product Regulations Group San Diego Division (SDD) Tel : 619 655 3329 16399 West Bernardo Drive FAX : 619 655 4979 San Diego, California 92127 e-mail: ri...@sdd.hp.com -
RE: Comparative Tracking Index
Hello Rich: it is a challenge to find a flame retardant material with a good CTI rating. The flame retardant in use tend to lower CTI ratings. - Mel -- From: Rick Busche[SMTP:rbus...@es.com] Sent: Thursday, February 19, 1998 12:23 PM To: emc-p...@ieee.org Subject:Comparative Tracking Index 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 rbus...@es.com
Re: Comparative Tracking Index
Hi Rick: You ask about CTI for printed wiring boards, and typical values. According to the UL Yellow Book, CTI is indicated in volts. In glancing through the UL Yellow Book, very few board manufacturers have submitted their boards for CTI. The few that have submitted, have CTIs in the range of less than 100 up to about 250. A very few manufacturers can provide boards with CTI exceeding 600. Best regards, Rich "Life is ours to be spent, not to be saved." -- D. H. Lawrence - Richard Nute Quality Department Hewlett-Packard Company Product Regulations Group San Diego Division (SDD) Tel : 619 655 3329 16399 West Bernardo Drive FAX : 619 655 4979 San Diego, California 92127 e-mail: ri...@sdd.hp.com -
Re: Comparative Tracking Index
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 (rbus...@es.com) at HP-Boise,mimegw150 List-Post: emc-pstc@listserv.ieee.org 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 rbus...@es.com
Comparative Tracking Index (CTI) question
Can anyone tell me if the UL CTI ratings/results are the same as the IEC 112 CTI. Many EN and harmonized standards use CTI for determining creepage requirements but is the CTI number in the UL Recognized Component Directory a valid number for this value? Thanks, Steve Costello National Instruments steve.coste...@natinst.com
Re: Comparative Tracking Index (CTI) question
In reply to Mr. Costello's CTI question, we asked similar questions directly to UL Santa Clara in July this year. Our questions were concerning UL 1950 (3rd ed.), Cl. 2.9.3 CTI requirements. Q. Does "IEC 112 Method A" described in UL 1950 (3rd) mean "Solution A"? A. Yes. Q. What are the differences between IEC 112 and ASTM D 3688-85? A. The main differences are the equipment used for conducting the tests and resistivity. UL has conducted comparison testing between IEC 112 Solution A and UL 746A (ASTM D 3688-85) and the result was pretty much the same. The IEC 112 has recently been revised and we are currently evaluating the revision through comparison testing. Q. Does UL accept the CTI value of UL 746A to determine a material group? A. Yes, we accept CTI value according to UL 746A for determining a material group. Q. Can UL test CTI in accordance with IEC 112, method A? A. Yes (prior to the revisions). Currently the test period is basically UL 746A. Currently, the test period is 4-5 weeks. We would require 10 samples (size 4x4) for the test. The RTP office is currently determining what testing would be necessary for the revised version of IEC 112, Method A. Hope this info is of help. We suggest that you confirm this directly with UL, as their requirements may be different in your specific situation. Also, they may have more information about the revisions to the IEC 112, and whether or not it affects the testing comparison between UL 746A and IEC 112. A-Pex International Co., Ltd. a-...@tcp-ip.or.jp > Can anyone tell me if the UL CTI ratings/results are the same as the > IEC 112 CTI. Many EN and harmonized standards use CTI for determining > creepage requirements but is the CTI number in the UL Recognized > Component Directory a valid number for this value? > > Thanks, > > Steve Costello > National Instruments > steve.coste...@natinst.com >
re: Comparative Tracking Index (CTI) question
You asked if UL CTI ratings are equivalent to IEC 112 CTI ratings. The simple answer is no. The test methods are different, therefore, there is no correlation. This is not my area of expertese, if you need more detailed information contact John Augis at our Santa Clara office: Phone: 408-985-2400 ext.32440 E-Mail: aug...@ul.com Usual disclaimers. _ Bob M. Miller Underwriters Laboratories Inc. Voice : (408) 985-2400 x32382 1655 Scott Blvd. Fax: (408) 296-3256 Santa Clara, CA 95050 E-mail: mill...@ul.com _
