SIEMENS
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Siemens IC 10 · 2017
Overload Relays
SIRIUS 3RB2 Electronic Overload Relays
3RB20, 3RB21 for standard applications
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SIRIUS 3RB2153-4FW2 electronic overload relay
The 3RB20 and 3RB21 electronic overload relays up to 630 A
with internal power supply have been designed for current-
dependent protection of loads with normal and heavy starting
(see Manual)
against excessive temperature rises due to
overload, phase asymmetry or phase failure.
An overload, phase asymmetry or phase failure result in an
increase of the motor current beyond the set rated motor current.
This current rise is detected by the current transformers inte-
grated into the devices and evaluated by corresponding solid-
state circuits which then output a pulse to the auxiliary contacts.
The auxiliary contacts then switch off the load by means of a
contactor. The break time depends on the ratio between the
tripping current and the current setting
I
e
and is stored in the
form of a long-term stable tripping characteristic curve,
see Characteristic curves
.
In addition to inverse-time delayed protection of loads against
excessive temperature rises due to overload, phase asymmetry
and phase failure, the 3RB21 electronic overload relays also
allow internal ground-fault detection (not possible in conjunction
with contactor assemblies for star-delta (wye-delta) starting).
This provides protection of loads against high-resistance short
circuits due to damage to the insulation material, moisture,
condensed water etc.
The "tripped" status is signaled by means of a switch position
indicator. The relay is reset manually or automatically after the
recovery time has elapsed.
The 3RB2 electronic overload relays are suitable for operation
with frequency converters,
see Manual
.
The devices are manufactured in accordance with environmen-
tal guidelines and contain environmentally friendly and reusable
materials. They comply with all important worldwide standards
and approvals.
For 3RB30 and 3RB31 overload relay sizes S00 to S3,
see
page 7/97 onwards
.
Use in hazardous areas
The 3RB20/3RB21 electronic overload relays are suitable for the
overload protection of motors with the following types of
protection:
•
II (2) G [Ex e] [Ex d] [Ex px]
•
II (2) D [Ex t] [Ex p]
EC type test certificate for Group II, Category (2) G/D exists. It
has the number PTB 06 ATEX 3001.
;
Connection for mounting onto contactors:
Optimally adapted in electrical, mechanical and design terms to the
contactors 3RT1. These connecting pins can be used for direct
mounting of the overload relay to the contactor. Stand-alone
installation is possible as an alternative (partly in conjunction with a
terminal bracket for stand-alone installation).
Selector switch for manual/automatic RESET:
With the slide switch you can choose between manual and
automatic RESET.
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Switch position indicator and TEST function of the wiring:
Indicates a trip and enables the wiring test.
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Solid-state test (device test):
Enables a test of all important device components and functions.
3
Motor current setting:
Setting the device to the rated motor current is easy with the large
rotary knob.
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Trip class setting/internal ground-fault detection (only 3RB21):
Using the rotary switch you can set the required trip class and
activate the internal ground-fault detection dependent on the
start-up conditions.
2
Connecting terminals (removable terminal block for auxiliary circuits):
The generously sized terminals permit connection of two
conductors with different cross-sections for the main and auxiliary
circuits. The auxiliary circuit can be connected with screw terminals
and alternatively with spring-type terminals.
4
A device set to manual RESET can be reset locally by pressing the
RESET button. On the 3RB
21 overload relay a
solid-state remote
RESET is integrated.
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IC01_00335a
© Siemens AG 2016