> From: Piotr Galka > Sent: Thursday, April 26, 2007 4:48 AM > > All 60950-1 Experts, > > I have in my device RS232 input line. > > I need to protect it against surge (because of EN 50130-4). > > Is it true that if I use the 33V varistor I will need to add > a fuse in series with it (Cl. 1.5.9.2), but if I use the 33V > TVS I need not to add the fuse.
Hi, Piotr. That appears to be true, if the text is taken literally), but it doesn't make sense, considering §1.5.9.2, Note 2, so I'm not certain that was the intent. VDRs could be a concern for increased leakage current in TNV-2 and TNV-3 circuits (remember that ringing voltages are applied during some touch current tests), but I don't think the intent was to apply this to all data bus circuits that typically do not contributing much to touch currents and for which transients are not considered in touch current testing. > Cl. 1.5.9.1 note 1 tells me that TVS is not VDR (in 60950-1), > so 1.5.9.2 not apply to it. A VDR is still a TVS. §1.5.9.1, Note 1, only intends to differentiate which are considered VDRs and which are not. > Reading Cl. 2.4 I understand that 12V/10mA (RS232 driver > capability) is not the LIMITED CURRENT CIRCUIT so VDR needs fuse. Again, if literally taken, you'd be correct. > If the fuse is needed do the PTC resistor (for example > Raychem miniSMDC020 - 0.2A/30VDC) can be considered as "an > interrupting means having an adequate breaking capacity" ? Probably, but it may depend on how the RS-232 circuit is used, the anticipated transients and the power supply capacity. > If not the fuse with what approval should I look for ? I don't understand this question. Can you be more specific? > In my opinion the same what can happen to the varistor during > "-temporary overvoltages above the maximum continuous > voltage." can happen to TVS. True, but other TVS devices have generally proven themselves more immune to the kinds of problems VDRs exhibit, provided they are rated appropriately for the application. CONFIDENTIALITY This e-mail message and any attachments thereto, is intended only for use by the addressee(s) named herein and may contain legally privileged and/or confidential information. If you are not the intended recipient of this e-mail message, you are hereby notified that any dissemination, distribution or copying of this e-mail message, and any attachments thereto, is strictly prohibited. If you have received this e-mail message in error, please immediately notify the sender and permanently delete the original and any copies of this email and any prints thereof. ABSENT AN EXPRESS STATEMENT TO THE CONTRARY HEREINABOVE, THIS E-MAIL IS NOT INTENDED AS A SUBSTITUTE FOR A WRITING. Notwithstanding the Uniform Electronic Transactions Act or the applicability of any other law of similar substance and effect, absent an express statement to the contrary hereinabove, this e-mail message its contents, and any attachments hereto are not intended to represent an offer or acceptance to enter into a contract and are not otherwise intended to bind the sender, Sanmina-SCI Corporation (or any of its subsidiaries), or any other person or entity. _____________________________________________________________________________ Scanned by Sanmina-SCI eShield _______ _____________________________________________________________________ - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
