ART815650.book Page 80 Lundi, 6. février 2006 10:18 10
Technical aspects
Protection using Vigirex RCDs
Protection of persons (cont.)
Type of contact
DB106993
The standards and regulations distinguish two types of potentially dangerous
contacts and indicate the corresponding protection techniques.
b direct contact: contact of a person with live conductors (phase or neutral) or with
conductive parts that are habitually live.
Protection against direct contact is normally provided by insulation of the live parts
using barriers, screens or enclosures (as per standard IEC 60364-4-41 or
NF C 15-100). These systems are preventive in nature and may fail. That is why
additional protection is installed, in the form of a high-sensitivity RCD that
automatically breaks the circuit. The operating threshold is set to 30 mA for AC
current (IEC 60364-4-41 or NF C 15-100) and 60 mA for DC current.
The sensitivity of RC protection devices, designed to limit the current flowing through
the body to a maximum of 30 mA, provides a very high level of safety and maintains
a good continuity of service.
Direct contact.
DB107097
Detection
Comparison between 10 mA and 30 mA sensitivities
An RCD set to 10 mA will trip somewhat more quickly than an RCD set to 30 mA.
But a 10 mA setting significantly increases the risk of disturbing the continuity of
service due to nuisance tripping caused by natural leakage currents.
Comparison between 10 mA and 30 mA.
DB106995
b indirect contact: contact of a person with exposed conductive parts that are
normally not live, but may become live by accident. This situation is due to failure of
the insulation for a device or conductor, resulting in an insulation fault.
The electrical risk depends on the touch voltage between the exposed conductive
parts of the faulty equipment and earth or other exposed conductive parts located
nearby.
The design of protection devices based on the physiological thresholds stipulated in
IEC standard 60479 and complying with the rules defined in standard IEC 60364 has
made it possible to create safe electrical installations.
Indirect contact.
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