Hi Mel,
Right on the money, the provision only apply to clause 2.2.7.4 for
determining the creepage requirement.
Best Regards
P.Lim
______________________________ Reply Separator _________________________________
Subject: RE: Re[2]: ammendment 4 TNV working voltage determination
Author: [email protected] at Supernet
List-Post: [email protected]
Date: 4/7/97 11:03 AM
Hello Peter: True, but you may only disregard ringing voltages for determining
c reepage distances...for determining clearance distances and the appropriate
elect rical strength test voltages, you must still consider the ringing voltage.
See c lauses 2.2.7.3 and 2.2.7.5 of either UL1950 3rd edition, or the IEC 940
4th amend ment 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
shal
l be used." Neither clause concerning clearance or electrical strength says you
may disregard ringing voltage; the statement allowing one to disregard ringing
v oltages 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.
