Hi George:
> Could someone give me an explanation of what makes a power source
> "Inherently Limited"..
Others have provided excellent responses to your question.
Perhaps I can embellish their answers.
A doorbell transformer is the prime example of an inherently
limited power source.
The requirements originally were published in the National
Electrical Code, Article 725. They were picked up by UL in
many of their standards. Now, the NEC makes reference to one
of those UL standards, UL 1950, as the authoritative source
for Limited Power, both inherently limited and not inherently
limited.
The simple answer to your question is:
Any source that meets the requirements and does not use
a fuse.
So, electronic circuits that limit the power (under both normal
and single-fault conditions) without reliance on a fuse are
deemed "inherently limited." Inherently limited circuits need
not be limited by an impedance, although that has been the
tradition.
Best regards,
Rich
-------------------------------------------------------------
Richard Nute Product Safety Engineer
Hewlett-Packard Company Product Regulations Group
AiO Division Tel : +1 858 655 3329
16399 West Bernardo Drive FAX : +1 858 655 4979
San Diego, California 92127 e-mail: [email protected]
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