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3RU11, 3RB10, and 3RB12 overload relays
SIRIUS System Manual
4-12
GWA 4NEB 430 0999-02b
Variants
The 3RB12 electronic overload relays are available in the following variants:
• Output relay with monostable behavior
• Output relay with bistable behavior
• For the following control supply voltages:
24 VDC
110 VAC to 120 VAC
220 VAC to 240 VAC
Auxiliary contact ele-
ments
The 3RB12 electronic overload relays have electrically isolated auxiliary con-
tact elements with the following functions (depending on the variant):
• 1 NO contact/1 NC contact for overload tripping through current and/or
thermistor
1 NO contact/1 NC contact for ground fault tripping
• 1 NO contact/1 NC contact for overload tripping through current and/or
thermistor and ground fault; 1 NO contact/1 NC contact for overload
warning
Overload protection
The currently flowing motor current is detected in each motor supply line by
current transformers and constantly monitored by a microprocessor.
An overload warning occurs as of:
• 1.15 x
I
e
in the case of a symmetric load
• 0.85 x
I
e
in the case of an asymmetric load
The overload warning is indicated by the flashing "Overload" LED on the
overload relay or externally by means of 1 NO contact/1 NC contact.
Thermistor motor pro-
tection
The continuous evaluation of a PTC thermistor detector ensures thermistor
motor protection.
Additional thermistor motor protection (full motor protection) is imple-
mented by connecting a PTC thermistor detector (PTC sensor circuit in the
motor winding). This is important for stator-critical motors, motors with long
starting and braking, and motors with cooling systems problems or with
high ambient temperatures.
No additional equipment is required for evaluation purposes.
Full motor protection is deactivated on delivery by means of a wire jumper.
The monitoring of the thermistor is secure against a wire break. In other
words, tripping occurs in the event of a wire break.
Ground fault protection
Internal ground fault monitoring
The ground fault protection integrated in the overload relay monitors motors
with a three-conductor terminal. Ground faults are detected in the event of
fault currents > 30 % of the set current
I
e
in rated service.
External ground fault monitoring
External ground fault protection is implemented by connecting a 3UL220.-.A
summation current transformer and monitors motors with three- and four-
conductor terminals. Ground faults are detected reliably in the event of fault
currents of 0.3 A, 0.5 A and 1 A. These values refer to sinusoidal fault cur-
rents 50/60 Hz.
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