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4.3
Special application cases
Overload relays in contactor assemblies for star-delta (wye-delta) start
When using the 3RB24 solid-state overload relay in conjunction with contactor assemblies for
star-delta (wye-delta) start, you need to bear in mind that only 0.58 times the motor current
flows through the line contactor. The solid-state overload relay mounted onto the line contactor
must be set to this level of 0.58 times the motor current.
Note
When using the 3RB24 solid-state overload relay in conjunction with contactor assemblies for
start-delta (wye-delta) start, internal ground fault detection must not be enabled on the
overload relay.
Overload protection of motors in hazardous environments
The 3RB24 solid-state overload relay for IO‑Link with monostable relays is suitable for overload
protection of explosion-proof motors. The device must only be used outside the hazardous area
for protecting explosion-proof electric motors in accordance with RL94/9/EG Group II of
Category 2 and 3 (gas: Zone 1 and 2 or dust : Zone 21 and 22).
Note
When using motors in hazardous environments, the information in the Safety and
commissioning instructions (http://support.automation.siemens.com/WW/view/en/22712155)
must be observed at all times.
Operation with frequency converter
The 3RB24 solid-state overload relay is suitable for frequencies of 50/60 Hz and their associated
harmonics. This makes it possible to use the solid-state overload relay on the input side of the
frequency converter. If motor protection is required in the outgoing circuit of the frequency
converter, the 3RN thermistor motor protection devices or the 3RU thermal overload relays are
recommended.
Operation with loads in excess of 630 A rated operational current
The 3RB24 solid-state overload relay for IO‑Link can also be used for protecting loads up to 820 A
by means of an external 3UF1868‑3GA00 current transformer . The secondary cables of the
current transformer are looped through the three feed-through openings of the current
measuring module, and short-circuited. The secondary current of the external current
transformer is the primary current of the 3RB29 current measuring module of the 3RB24 solid-
state overload relay. You can find a connection example in the Chapter "Circuit diagrams
(Page 115)".
SIRIUS 3RB24 electronic overload relay for IO-Link
Equipment Manual, 07/2022, NEB969165602000/RS-AA/003
Use planning
4.3 Special application cases
37
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