Brochure

SIRIUS
Siemens Industry, Inc. Industrial Control Product Catalog 2017
3/20
3
OVERlOAd
RElAYS
Function
Basic functions
The 3RB2 / 3RB3 solid-state overload relays are designed for:
• Inverse-time delayed protection of loads from overloading
• Inverse-time delayed protection of loads from phase
unbalance
• Inverse-time delayed protection of loads from phase failure
• Protection of loads from high-resistance short-circuits
(internal ground-fault detection only with 3RB21 / 31).
Control circuit
The 3RB2 / 3RB3 solid-state overload relays have an internal
power supply, i.e. no additional supply voltage is required.
Short-circuit protection
Fuses or motor starter protectors must be used for short-circuit
protection. For assignments of the corresponding short-circuit
protection devices to the 3RB2 / 3RB3 solid-state overload re-
lays with/without contactor see Technical Specifications and
Selection and Ordering Data.
Trip classes
The 3RB20 / 30 solid-state overload relays are available for
normal starting conditions with trip CLASS 10 or for heavy start-
ing conditions with trip CLASS 20 (fixed setting in each case).
The 3RB21 / 31 solid-state overload relays are suitable for normal
and heavy starting. The required trip class (CLASS 5, 10, 20 or
30) can be adjusted by means of a rotary knob depending on the
current starting condition.
For details of the trip classes see Characteristic Curves.
Phase failure protection
The 3RB2 / 3RB3 solid-state overload relays are fitted with
phase failure protection (see Characteristic Curves) in order to
minimize temperature rise of the load during single-phase
operation.
Phase failure protection is not effective for loads with star-
connection and a grounded neutral point or a neutral point which
is connected to a neutral conductor.
Setting
The 3RB2 / 3RB3 solid-state overload relays are set to the
motor rated current by means of a rotary knob. The scale of the
rotary knob is shown in amps.
With the 3RB21 / 31 solid-state overload relay it is also possible
to select the trip class (CLASS 5, 10, 20 or 30) using a second
rotary knob and to switch the internal ground-fault detection on
and off.
Manual and automatic reset
In the case of the 3RB2 / 3RB3 solid-state overload relays, a
slide switch can be used to choose between automatic and
manual resetting.
If manual reset is set, a reset can be carried out directly on the
device after a trip by pressing the blue RESET button. Resetting
is possible in combination with the mechanical reset options
from the accessories range (see Accessories). As an alternative
to the mechanical RESET options, the 3RB21 / 31 solid-state over-
load relays are equipped with an electrical remote RESET which
may be utilized by applying a voltage of 24 V DC to the terminals
A3 and A4.
If the slide switch is set to automatic RESET, the relay is reset
automatically.
The time between tripping and resetting is determined by the
recovery time.
Recovery time
With the 3RB2 / 3RB3 solid-state overload relays the recovery
time after inverse-time delayed tripping is between 0.5 and 3
minutes depending on the preloading when automatic RESET
is set. These recovery times allow the load (e.g. motor) to
cool down.
If the button is set to manual RESET, the 3RB2 / 3RB3 devices
can be reset immediately after inverse-time delayed tripping.
After a ground fault trip the 3RB21 / 31 solid-state overload relays
(with ground-fault detection activated) can be reset immediately
without a recovery time regardless of the reset mode set.
TEST function
With motor current flowing, the TEST button can be used to
check whether the relay is working correctly (device/solid-state
TEST). Current measurement, motor model and trip unit are
tested. If these components are OK, the device is tripped in
accordance with the table below. If there is an error, no tripping
takes place.
Note: The test button must be kept pressed throughout the test.
Testing of the auxiliary contacts and the control current wiring is
possible with the switch position indicator slide. Actuating the
slide simulates tripping of the relay. During this simulation the NC
contact (95-96) is opened and the NO contact (97-98) is closed.
This tests whether the auxiliary circuit has been correctly wired.
After a test trip the relay is reset by pressing the RESET button.
Self-monitoring
The 3RB2 / 3RB3 solid-state overload relays have a self-moni-
toring feature, i.e. the devices constantly monitor their own basic
functions and trip if an internal fault is detected.
Display of operating status
The respective operating status of the 3RB2 / 3RB3 solid-state
overload relays is displayed by means of the position of the
marking on the switch position indicator slide. After tripping due
to overload, phase failure, phase unbalance or ground fault
(ground fault detection possible only with 3RB21 / 31) the marking
on the slide is to the left on the "O" mark, otherwise it is on the "I"
mark.
Auxiliary contacts
The 3RB2 / 3RB3 solid-state overload relays are fitted with an
NO contact for the "tripped" signal, and an NC contact for
switching off the contactor.
Trip class Required loading with the
rated current prior to press-
ing the test button
Tripping within
CLASS 5
2 min 8 s
CLASS 10
4 min 15 s
CLASS 20
8 min 30 s
CLASS 30
12 min 45 s
Overload Relays
3RB2 / 3RB3 Solid-State Overload Relays
3RB20, 3RB21, 3RB30, 3RB31 up to 630A for standard applications