Hi Kaan:
If memory serves me correctly, IEC 950 First Edition defined
ELV (and therefore SELV) as:
30 V rms
42.4 V peak (1.414 x 30)
42.4 V dc (1.414 x 30)
The Second Edition defined ELV as:
30 V rms
42.4 V peak (1.414 x 30)
60 V dc
The 60 V dc limit came from the integration of telephone
requirements into Clause 6 of the standard.
The first point for acceptance is that the telephone industry
has been using potientials up to 60 V dc for years with no
hazardous results.
The second point for acceptance of 60 V dc is that dc does
not cause tetanization (can't-let-go).
The third point for acceptance is that typical points of
accessiblity to 60 V dc are very small area (~1 square mm)
and only to tips of fingers which are commonly relatively
callused and therefore higher resistance.
Note that SELV is not defined by voltage alone. It is further
defined by its isolation from high voltage sources. In other
words, SELV is a special case of ELV. The unique feature of
SELV is that it must be isolated from higher voltages to the
same degree as any accessible part.
Best regards,
Rich
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Richard Nute Quality Department
Hewlett-Packard Company Product Regulations Group
San Diego Division (SDD) Tel : 619 655 3329
16399 West Bernardo Drive FAX : 619 655 4979
San Diego, California 92127 e-mail: [email protected]
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