-Original Message-
From: Art Michael [SMTP:amich...@connix.com]
Sent: Friday, July 09, 1999 9:55 AM
To: emc-p...@ieee.org
Cc: Sparacino,George
Subject:Re: Inherently Limited power source..
Hello George,
An Inherently Limited power source is one in which the impedance of the
source, typically a transformers' primary or secondary, is such that the
available output is limited within the constraints of low energy as
defined by a standard. UL 1585, for example, describes the
limits/requisites for such a trafo design and the means for determining
the power available. There is also an IEC standard for such transformers,
but it's number does not come to mind at this instant. I'm certain someone
else on this listserver can provide that bit of info.
I also believe that if a non-accessible, non-replaceable current limiting
device (film-resistor, fuse or ptc, for example) is housed within the
transformer, the output can also be determined to be Inherently Limited.
For UL 1310 (Class 2 Direct Plug In) an automatic reset device (ie. PTC)
will not qualify as Inherently Limited. My experience with UL is that
fuses are normally preferred for Inherently Limited if the xfmr is not
designed as Art described. what Standard are you evaluating to? IBTW, I
believe the IEC Standard is 61558-2-6.
Also, if considering an Inherently Limited power source, other than a
transformer, the same principles apply.
Best Regards,
Jody Leber
jle...@ustech-lab.com
http://www.ustech-lab.com
U. S. Technologies
3505 Francis Circle
Alpharetta, GA 30004
770.740.0717
Fax: 770.740.1508
Regards, Art Michael
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On Fri, 9 Jul 1999 sparaci...@andovercontrols.com wrote:
Hello all,
The standard that I'm working with states under Power Limited Circuits
that:
an Inherently Limited power source does not require overcurrent
protection, while a Not Inherently Limited power source does require
it.
Could someone give me an explanation of what makes a power source
Inherently Limited..
Thank You,
George
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