Siemens SIRIUS 3RH Series - Configuration; Overload Relays in Motor Feeders

SIRIUS 3RU2/3RB3 overload relays
5.5 Configuration
SIRIUS Innovations
System Manual, 01/2011, A8E56203870002-03
503
5.5 Configuration
5.5.1 Overload relays in motor feeders
5.5.1.1 Overload relays in motor feeders
The individual overload relay families protect the following loads against the consequences
of an overload, a phase failure, and phase asymmetry.
Table 5- 8 Overload relays in motor feeders
For the protection of 3RU21 3RB30/3RB31
Three-phase current loads ✓ ✓
DC loads ✓ -
Single-phase AC loads ✓ -
Note
In the case of three-phase current loads, only 3-pole circuits (3 phases) are permitted.
4-pole circuits (3 phases + neutral conductor) are not permitted.
NOTICE
Design of motor feeders
An overload relay alone cannot protect a load against overload. The overload relay simply
detects the current, evaluates it, and switches the auxiliary contacts according to the
relevant tripping characteristic curve. The connected contactor, and thus the load, are
disconnected via the auxiliary contacts.
A protective device such as a motor starter protector/circuit breaker (acc. to UL) or fuses
must be installed upstream of the load to provide protection against short circuits.