Hello Peter: True, but you may only disregard ringing voltages for determining creepage distances...for determining clearance distances and the appropriate electrical strength test voltages, you must still consider the ringing voltage. See clauses 2.2.7.3 and 2.2.7.5 of either UL1950 3rd edition, or the IEC 940 4th amendment text that you have. 2.2.7.5 (concerning electrical strength testing) says "...D.C. voltages and peak values for other voltages." Clause 2.2.7.3 (concerning clearance distances) says "...for non-sinusoidal wave forms, the peak value shall be used." Neither clause concerning clearance or electrical strength says you may disregard ringing voltage; the statement allowing one to disregard ringing voltages only applies to determination of creepage distances.
Regards and have a nice weekend! Mel Pedersen Midcom, Inc. Homologations Engineer Phone: (605) 882-8535 [email protected] Fax: (605) 886-6752 ---------- From: [email protected][SMTP:[email protected]] Sent: Friday, April 04, 1997 3:24 AM To: [email protected] Subject: Re[2]: ammendment 4 TNV working voltage determination Dear Mel I have just received a copy of the proposal for changes on IT/TE UL/CSA std. 950/1950 respectively (dated Feb 6. 97). On page 3, under the review of the fourth amendment to IEC 950, second edition, it mentioned that clause 2.2.7.4, the considerations associated with the existing D3 deviations have been incorporated into the fourth amendment to IEC 950, second edition. That is, you may disregard the ringing voltage. Also, the committee of the bi-national std recommended that the existing D3 deviation on the ninational std be dropped and adapt the IEC 950 fourth amendment text. Rgds. P.Lim ______________________________ Reply Separator _________________________________ Subject: Re: ammendment 4 TNV working voltage determination Author: Peter Lim at VTNCAN List-Post: [email protected] Date: 4/2/97 11:39 AM Dear Joe and Jim: For what its worth, I believe that there is something missing (probably, in most cases a minor detail) from your determination of working voltage using IEC 950 am endment 4...for creepage distance only, in determining working voltage for TNV-2 and TNV-3 (Amd. 4, section 2.2.7.4), is the ringing voltage disregarded. However , it is not disregarded in determining creepage distance or the appropriate elect rical strength test (see section 2.2.7.3 and 2.2.7.5). In these cases, the peak value of ringing voltage should be used. I have not seen the amend. 4, as far as I know, under the amendment 3, you need to consider the ringing voltage for IEC 950. Only UL1950 under the clause 2.2.7.4 allows for deviation D3 which call for disregard short term disturbances (e.g. incadenced ringing signals). P.Lim Comments anyone? Mel Pedersen Midcom, Inc. Homologations Engineer Phone: (605) 882-8535 [email protected] Fax: (605) 886-6752 ---------- From: [email protected][SMTP:[email protected]] Sent: Thursday, March 13, 1997 8:11 AM To: [email protected] Cc: jimwiese Subject: Re: ST interfaces and safety requirements for Japan In a message dated 97-03-13, Jim Wiese writes the following with reference to amendment 4 of IEC 950: << There also seems to be some confusion amongst test labs as to what "working voltage" to apply to the interface. Some say 240 VAC regardless of how it powered, even though Japan uses 100 VAC as I remember. Others say it is the output voltage of the transformer (assuming it meets the appropriate requirements to make the output SELV), and yet others have told me it is the maximum operating voltage on the telco interface. Any Thoughts? >> Jim: I will venture an opinion on this one. Under clause 6.3.3 of IEC 950 with A1, A2, and A3 (but not A4), the "working voltage" would be the AC mains voltage. This is because clause 6.3.3 is specifically targeted at a fault condition (mis-wired plug) that inadvertantly connects the chassis ground to the AC mains voltage. If the product was exclusively for Japan, the working voltage would be 100 volts RMS. The insulation barrier would have to meet the requirements for supplementary insulation with a working voltage of 100 volts, which invokes creepage, clearance, distance-through insulation, and an electric strength test). Clause 6.4.2.2 imposes an additional dielectric strength test of either 1000 or 1500 volts RMS. In Amendment 4, the test in clause 6.3.3 has been changed so that it simply points to clause 6.4.2.2. Thus, under Amendment 4, clause 6.3.3 has been reduced to a simple dielectric strength test of 1000 or 1500 volts RMS (except for Sweden, which retains the requirement for supplementary insulation at the rated AC mains voltage). Creepage, clearance, and distance through insulation are no longer invoked by clause 6.3.3, except for Sweden. However, Amendment 4 has expanded clause 6.2.1.2 to address the three types of TNV circuits. In some cases, basic insulation is required. In the event that basic insulation is required, it becomes necessary to identify the working voltage in order to determine the required creepage, clearance, and dielectric strength (distance through insulation is not specified for basic insulation). In this case, the working voltage is the voltage on the TNV circuit, NOT the AC mains. However, in the specific case of the S/T interface, not even basic insulation is required. The S/T interface is a "TNV-1" circuit, and clause 6.2.1.2 only calls out clause 6.4.1 for separation of SELV and TNV-1. Clause 6.4.1 leads back to the same 1000 and 1500 volt RMS dielectric strength tests described in clause 6.4.2.2. So, my conclusion is that under amendment 4, for your specific application (S/T interface), there is no need to concern yourself with the "working voltage" at all. You only have to deal with the dielectric strength tests in clause 6.4.2.2. For separation of TNV-2 or TNV-3 circuits from SELV, amendment 4 calls for basic insulation, and the "working voltage" for this insulation is the steady-state voltage on the TNV circuit (ringing signals are not considered in the determination of working voltage). Well, that is my interpretation of how amendment 4 changes the situation for your product. To be honest, I have not spent a lot of time with this because, to my knowledge, amendment 4 has not yet been incorporated into EN 60950. Having it in IEC 950 is nice, but in Europe, EN 60950 is the one that counts. This raises a cautionary note. When someone tell you that Japan uses "IEC 950," make sure that they mean exactly that. In particular, make sure that Japan formally recognizes amendment 4 to IEC 950. In some cases (such as in Europe), there is an administrative delay between the time that the IEC adopts an amendment, and the time that the amendment becomes officially recognized. IEC 950, by itself, is just a reference standard. To have the force of law in a given country, it must be formally adopted or recognized in some way. Let me close this with a question. Does ANYONE on treg know when amendment 4 will be formally adopted as part of EN 60950? I believe that the critical step is for amendment 4 to be referenced in the Official Journal of the EC. I have heard that amendment 4 went out for voting last fall, but I have heard nothing since. I sure would like to know when I can begin using amendment 4 in Europe. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc.
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