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SIVACON S8 Planning Principles – Technical annex
observed. In accordance with IEC 60364-5-54, a minimum
clearance ≥ 15 m is required.
Networks with an IT system are preferably used for rooms
with medical applications in accordance with IEC 60364-7-
710 in hospitals and in production, where no supply inter-
ruption is to take place upon the first fault, for example in
the cable and optical waveguide production. The TT system
as well as the IT system require the use of residual current
devices (RCDs) – previously named FI (fault interrupters)
– for almost every circuit.
Fault in the IT network
In the IT network, it is the phase-earth-phase fault – or
double fault – which has to be managed by the cir-
cuit-breaker as the worst case fault at the load and supply
side (Fig. 10/3). During such a fault, the full phase-to-phase
voltage of 690 V, for example, is applied to the main con-
tact, and simultaneously the high short-circuit current.
The product standard IEC 60947-2 for circuit-breakers calls
for additional tests in accordance with Annex H of this
standard to qualify them for use in non-earthed or imped-
ance-earthed networks (IT systems). Accordingly, cir-
cuit-breaker specifications relating to the IT system must be
observed.
Fig. 10/3: Double fault in the IT system
690 V
3-phase 690 V AC
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