Product description
3.3 Applications
SIRIUS 3RU thermal overload relays / SIRIUS 3RB electronic overload relays
Manual, 09/2016, A5E03656507420A/RS-AB/003
21
3.3 Applications
Table 3- 4 Overview of applications
Applications 3RU21 3RB20 / 3RB21
3RB30 / 3RB31
System protection ✓
1)
✓
1)
Motor protection ✓ ✓
Alternating current, 3-phase ✓ ✓
Alternating current, 1-phase ✓ -
DC current ✓ -
1)
In the main circuit, the devices provide overload protection for the assigned electrical loads (e.g.
motors), feeder cable, and other switching and protection devices in the respective load feeder.
The 3 phases have to be under symmetrical load.
3RU21 thermal overload relays
3RU21 thermal overload relays have been designed to protect three-phase loads, DC loads,
and single-phase AC loads.
Note
Protection of DC loads/single-phase AC loads
If a 3RU21 thermal overload relay is to be used to protect DC loads or single-phase AC
loads, all the bimetal strips have to be heated. Therefore, all of the relay's main current paths
have to be connected in series.
3RB20 / 3RB21 and 3RB30 / 3RB31 electronic overload relays
3RB20 / 3RB21 and 3RB30 / 3RB31 electronic overload relays are designed to protect
three-phase loads in sinusoidal 50/60 Hz voltage supplies.
Note
DC loads/Single-phase AC loads
The relay is not suitable for protecting DC loads or single-phase AC loads. On single-pole
loads, the 3RU21 thermal overload relay or the 3RB22, 3RB23 and 3RB24 electronic
overload relays for higher applications (no protection for DC loads) must be used for IO-Link.
Reference
More information ... Can be found in the chapter titled ...
About overload relay applications
Configuration (Page 59)
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