Applications; Use In Systems With Isolated Transformer Neutral Point (It Systems); General - Siemens SENTRON 3WA1 Manual

Applications

3.1 Use in systems with isolated transformer neutral point
(IT systems)
3.1.1

General

IT systems are predominantly used in consumer installations with stringent requirements
with respect to power supply availability. Circuits are generally only interrupted if two
insulation faults occur simultaneously in different phases.
The IT network type is the preferred choice in the following areas, for example:
• Buildings with rooms used for medical purposes
• Chemical industry
• Mineral oil industry
• Steel industry
• Mining
The IT system is a low-voltage system for supplying electrical power with increased fail-
safety in the event of ground faults. It is operated without connection of the live
conductors to ground. The 3WA circuit breaker is the perfect solution for protecting
these systems.
A ground fault does not result in system shutdown and the system can continue to
operate. The standard IEC 60364-4-41 (VDE 0100-410) therefore requires insulation
monitoring to indicate a fault of this kind. In the unusual event that a fault on the load
side coincides with a second fault on the infeed side, the full line-to-line voltage is
connected across one contact of the circuit breaker.
For this reason, the 3WA circuit breakers are tested up to a maximum voltage of 690 V
AC in accordance with standard IEC / DIN EN 60947-2 Annex H and are suitable for use
in IT systems.
3WA1 air circuit breaker
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