Hi Lauren:
The IEC and UL are not harmonized with
respect to safe DC voltages.
DC does not cause tetanization, and requires
very much more current to cause fibrillation
than AC. So, higher DC voltages provide the
same effect as AC voltages.
UL has taken the peak of the AC (30 V) as the
limit for DC (42.4 V). For telephone circuits,
UL uses 70 V DC.
All we can say is that the two organizations
are not yet fully harmonized as to hazardous
voltages.
Best regards,
Rich
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
[email protected]
Sent: Thursday, July 30, 2009 7:18 AM
To: [email protected]
Subject: "safe" voltage differences between UL 1703 and IEC 61140
A colleague has stumped me with the following question.
==================
A supplier of a Photovoltaic panel cited IEC 61140 (Protection against
electric shock – Common aspects for installation and equipment) as
referencing a "safe" voltage to be as high as 120 Vdc. This is puzzling
because UL 1703 (Flat-Plate Photovoltaic Modules and Panels) appears to define
the electric shock threshold at 30 Vdc. How can electric shock threshold for
UL 1703 be set at 30 Vdc, but IEC 61140 considers the upper "safe" limit to
be 120 Vd.c.?
**************************************
************************************************************************
IEC 61140 - Protection against electrical shock - common aspects for
installation and equipment
Section 7.4 Class III Equipment
Equipment relying on limitation of voltage to ELV values as provision
for
basic protection and with no provision for fault protection.
7.4.1 Voltages
7.4.1.1 Equipment shall be designed for a maximum nominal voltage not
exceeding 50V a.c. or 120 V d.c. ripple free.
...
NOTE 2: According to clause 411 of IEC 60264-4-41, class III equipment
is
accepted only for connection to SELV and PELV systems.
**************************************
**************************************************************************
Any ideas on the rational behind this difference?
Regards,
Lauren Crane
Product Regulatory Analyst
Corporate Product EHS Lead
Applied Materials Inc.
Austin, TX 512 272-6540 [#922 26540]
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