Siemens 3UG4 User Manual page 214

3UG458. insulation monitoring relay
The insulation monitoring relays monitor the following fault types, depending on the version:
● Open circuit
● Incorrect settings
● Ungrounded, strictly AC systems for insulation faults
● Ungrounded, strictly DC systems for insulation faults
● Ungrounded, mixed DC systems and AC systems for insulation faults (e.g. AC systems
with rectifiers or switched-mode power supplies)
Note
The use of two 3UG458 devices in a galvanically connected area (monitored area) is not
permissible.
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214
Monitored area
3UG4 / 3RR2 monitoring relays
Manual, 05/2016, NEB927043002000/RS-AC/004