Siemens 3RB12 - User Manual

Need help?

Do you have a question about the Siemens 3RB12 and is the answer not in the manual?

Summary

Device Description

Limited Touch Protection

Details degree of protection against direct contact and shock-proofing for installation personnel.

Protection Mechanisms Overview

Explains the 3RB12's overload, thermistor, and earth-fault protection capabilities for electrical equipment.

Installation and Connections

Mounting and Installation Details

Provides information on mounting positions and methods for 70 mm, 120 mm, 145 mm, and 230 mm devices.

Main Conductor Connection Methods

Details connection of main conductors, including current ranges and looping techniques for different motor currents.

Single-Phase Motor Connection

Explains how to protect single-phase AC motors by looping phase L through the device, referencing Fig. III.

High Current and Auxiliary Connections

Covers busbar connections for 50-820A, auxiliary conductor connections, thermistor sensor connection, and connection schemes.

Operation and Control

Setting the Operating Current

Describes using the current setting range knob to select the appropriate current for the motor.

Adjusting Tripping Classes

Explains how to select the appropriate tripping characteristic using the class changeover switch.

Device Status and Indicators

Details the meaning of LED indicators and auxiliary switch statuses for different operational states like ready, overload, and earth fault.

Test Procedures

Outlines the procedure for testing the device using the Test/Reset button and the resulting LED and switch statuses.

Resetting the Device

Details methods for resetting the relay after tripping, including test button, remote reset, and automatic reset.

Technical Specifications

General Specifications and EMC

Lists compliance standards, EMC requirements, and general device specifications.

Physical and Electrical Ratings

Provides weight information for different device sizes and details rated control supply voltage and main circuit voltage ratings.

Circuit Parameters

Covers main circuit parameters like frequency, insulation voltage, ambient temperature, and auxiliary circuit contacts and switching capacity.

Protection Data

Details technical data for short-circuit protection, control circuit fuses, thermistor protection parameters, and earth fault protection.

Summary

Device Description

Limited Touch Protection

Details degree of protection against direct contact and shock-proofing for installation personnel.

Protection Mechanisms Overview

Explains the 3RB12's overload, thermistor, and earth-fault protection capabilities for electrical equipment.

Installation and Connections

Mounting and Installation Details

Provides information on mounting positions and methods for 70 mm, 120 mm, 145 mm, and 230 mm devices.

Main Conductor Connection Methods

Details connection of main conductors, including current ranges and looping techniques for different motor currents.

Single-Phase Motor Connection

Explains how to protect single-phase AC motors by looping phase L through the device, referencing Fig. III.

High Current and Auxiliary Connections

Covers busbar connections for 50-820A, auxiliary conductor connections, thermistor sensor connection, and connection schemes.

Operation and Control

Setting the Operating Current

Describes using the current setting range knob to select the appropriate current for the motor.

Adjusting Tripping Classes

Explains how to select the appropriate tripping characteristic using the class changeover switch.

Device Status and Indicators

Details the meaning of LED indicators and auxiliary switch statuses for different operational states like ready, overload, and earth fault.

Test Procedures

Outlines the procedure for testing the device using the Test/Reset button and the resulting LED and switch statuses.

Resetting the Device

Details methods for resetting the relay after tripping, including test button, remote reset, and automatic reset.

Technical Specifications

General Specifications and EMC

Lists compliance standards, EMC requirements, and general device specifications.

Physical and Electrical Ratings

Provides weight information for different device sizes and details rated control supply voltage and main circuit voltage ratings.

Circuit Parameters

Covers main circuit parameters like frequency, insulation voltage, ambient temperature, and auxiliary circuit contacts and switching capacity.

Protection Data

Details technical data for short-circuit protection, control circuit fuses, thermistor protection parameters, and earth fault protection.

The Siemens 3RB12 is an electronic overload relay designed to protect electrical equipment, such as three-phase AC motors and transformers, using three distinct protection mechanisms.

Function Description

Overload Protection: The 3RB12 continuously compares the actual motor current with a user-defined set current. This comparison and evaluation are performed by an integrated microprocessor, ensuring precise overload detection.

Thermistor Protection: For enhanced thermal protection, the device incorporates PTC thermistors within the motor windings. These thermistors monitor the motor's temperature. If the temperature exceeds a predefined threshold, the relay triggers a trip, preventing thermal damage to the motor.

Earth-Fault Protection: The 3RB12 offers two types of earth-fault detection:

Internal Earth-Fault Detection: Available in specific versions, this feature is suitable for three-wire systems.
External Earth-Fault Detection: For applications requiring external monitoring, the device can be connected to an external summation current transformer (3UL22). This option supports both three-wire and four-wire systems.

Important Technical Specifications

General:

Degree of Protection (IEC 60529): IP 20 for devices 70 mm wide, IP 00 for devices > 70 mm wide.
Shock-Proof: Conforms to DIN VDE 0106, Part 100.
EMC (Electromagnetic Compatibility):
- Pulse packets (burst): IEC 61000-4-4, 2 kV
- Discharge of static electricity: IEC 61000-4-2, 8 kV
- Radiated high-frequency fields: IEC 61000-4-3, 3 V/m
- Surge voltage: IEC 61000-4-5, 2 kV
Permissible Ambient Temperature: -25 to +70 °C
Storage Temperature: -40 to +80 °C

Weight:

70 mm devices: 0.6 kg
120 mm devices: 1.0 kg
145 mm devices: 1.9 kg
230 mm devices: 3.2 kg

Rated Control Supply Voltage:

AC: 0.85 to 1.1 x Us; 2 VA (where Us is the rated control supply voltage)
DC (24 V): 0.85 to 1.2 x Us (DIN 19 240); 2W

Main Circuit:

Frequency: 50/60 Hz
Rated Insulation Voltage (Ui): 1000 V (for 3RB1246: 690 V)
Tripping Limit Values (three-pole symmetrical overload):
- Tripping current: 110...120% x Ie (where Ie is the set current)
- Tripping time: < 20 min

Auxiliary Circuit:

Contacts: 2 x (1 NO and 1 NC)
Electrical Isolation: Auxiliary switch is potential-free.
Rated Insulation Voltage (Ui): 300 V
Switching Capacity (IEC):
- AC-15: 6A/24V; 6A/120V; 3A/230V
- DC-13: 2A/24V; 0.55A/60V; 0.25A/125V
Switching Capacity (UL/CSA): B300, R300

Short-Circuit Protection:

Main Circuit: Short-circuit protection with fuses for motor feeders with short-circuit currents up to 50 kA at 690 V, 50/60 Hz (refer to catalog for specific data).
Control Circuit:
- Fuse links, duty class gL/gG: 6 A
- Quick-acting: 10 A
- Protective circuit-breaker: 1.6 A (C characteristic)

Thermistor Protection:

Sensor Connection: Thermistor sensor in the motor connects to terminals T1/T2.
Total Cold Resistance (Rcold): 1.5 kΩ
Measuring Circuit Loading: ≤ 5 mW (at Rcold = 1.5 kΩ)
Voltage at Sensor Circuit: ≤ 2 V (at Rcold = 1.5 kΩ)
Response Value: 2.7 to 3.1 kΩ
Return Value: 1.5 to 1.65 kΩ

Earth-Fault Protection (based on sinusoidal fault currents of 50/60 Hz):

External: Summation current transformers 3UL220.-.A are connected to terminals C1/C2. Pick-up delay is 200 ms ≤ t ≤ 500 ms.
Internal:
- With motor current between 0.3 and 2 times the set current: device trips at an earth-fault current of 30% of the set current.
- With motor current between 2 and 8 times the set current: device trips at an earth-fault current of 15% of the set current.
- Pick-up delay: 0.5 to 1 seconds.

Usage Features

Installation:

Mounting Position: Any.
70 mm Devices:
- Snap-on mounting on 35 mm mounting rail (EN 50 022).
- Screw mounting using inserted lugs (accessory 3RB1900-0B).
120 mm, 145 mm, and 230 mm Devices: Screw mounting integrated into the casing.
120 mm Devices (additional): Baseplate for snap-on fastening on 75 mm mounting rail (accessory 3UF1900-0J).

Main Conductor Connection:

Current Range up to 100 A:
- For rated motor currents from 1.25 A to 100 A: Insert motor leads per phase through openings (x).
- For rated motor currents less than 1.25 A: Insert motor leads per phase through openings (x), loop them back through opening (y), and re-insert through openings (x) to create two loops. A table specifies the number of loops for various rated motor currents.
- The device setting current (Ie) is calculated as Ie = n x IN (where n is the number of loops and IN is the rated motor current).
Current Range 50 A to 820 A (Busbar Connection):
- Uses M8, M10, or M12 screws depending on the device type and conductor size.
- Tightening torques range from 10 to 35 Nm (89 to 310 lb.in).
- Tag termination sizes vary from 20x4 mm to 40x8 mm.

Auxiliary Conductor Connection:

Supports finely stranded conductors with or without end sleeves (0.5 to 4 mm²) and solid conductors (0.5 to 2.5 mm²).
Uses connecting screws (0.8x4...5.5 mm) with Pozidriv 2.
Tightening torque: 0.8 to 1.2 Nm (7 to 11 lb.in).

Thermistor Sensor:

A link (A) is present upon delivery. This link must be removed when connecting the sensor.

Connection Scheme:

Circuit diagrams are provided for automatic and remote resets.
Includes facility for connecting the 3UL22 summation current transformer for external earth fault monitoring.

Operation:

Setting the Current: Use the current setting range knob to adjust the appropriate current.
Adjusting Tripping Classes:
- The motor, leads, and contactor must be rated for the selected class (Class 10 as delivered).
- Check and correct the class setting before initial start-up.
- Use the class changeover switch to select the appropriate tripping characteristic (refer to graphic section Fig. VII).
- In case of unsymmetry > 40% (NEMA) or phase failure, tripping occurs as shown in Fig. VIII. Characteristics apply to a cold start; tripping times (tA) are reduced for starting under full load.
- The current range setting knob and class changeover switch can be protected from tampering using the sealable cover plate 3RB1900-0A.

Device Statuses (via LEDs and Auxiliary Switches):

Device Ready for Operation (no overload, not tripped):
- Ready LED: Green steady light.
- Auxiliary switch: 95/96, 05/06 closed; 97/98, 07/08 open.
Overload Alarm (limit tripping current reached, tripping imminent):
- Overload LED: Red flashing light.
- Auxiliary switch: 05/06 open; 07/08 closed.
Overload Trip/Thermistor Trip:
- Overload LED: Red steady light.
- Auxiliary switch: 95/96 open; 97/98 closed.
Earth Fault Alarm:
- Gnd. Fault LED: Red steady light.
- Auxiliary switch: 05/06 open; 07/08 closed (for 3RB12..-...0, 3RB12..-...2); 95/96 open; 97/98 closed (for 3RB12..-...1, 3RB12..-...3).
Device Not Ready for Operation (control voltage failure):
- Ready LED: Dark.
- Auxiliary switch (monostable version): 95/96, 05/06 open; 97/98, 07/08 closed.
- Auxiliary switch (bistable version): Switching statuses are retained.

Test Function:

The Test/Reset button allows checking device status.
Press for up to 2 seconds: LEDs indicate current status (Ready, Gen. Fault, Overload). Auxiliary switching elements remain unchanged.
Press after 2 seconds: LEDs indicate status, and auxiliary switching elements reset.
Press for > 5 seconds: LEDs indicate status, and auxiliary switching elements reset.
A test with a duration of less than 5 seconds can be performed during operation without changing outputs in a fault-free state.

Reset Function:

Overload Trip: Can be reset immediately by briefly pressing the test/reset button or by remote reset (briefly pressing button at Y1-Y2). Automatic reset (bridging Y1-Y2) is also an option. After an overload trip, the device can be reset to operating mode after five minutes.
Thermistor Trip: Can be reset after the temperature has reached 5 K below the response temperature.
Earth Fault: Can be reset immediately by briefly pressing the test/reset button or by remote reset. Automatic reset is not effective for earth faults.
If both thermistor and overload have tripped simultaneously, the longer reset phase applies.
The protection functions are not impeded by holding down the test/reset button.

Maintenance Features

Installation and maintenance should only be performed by technical personnel.
Always follow the operating instructions.
WARNING: Hazardous voltage can cause electrical shock and burns. Disconnect power before proceeding with any work on this equipment.