SIEMENS 3RW4055-6BB44 Soft Starter

Discontinued (Siemens stopped delivery effective Oct 01, 2023), legacy obsolete model. Factory recommended replacement: 3RW5055-6AB14

1. Order Number Breakdown

3RW: SIRIUS soft starter series

40: Basic soft starter, built-in bypass, 2-phase thyristor control (Phase L1, L3)

55: S6 frame, rated current code 134A

6: Screw terminals

BB: Standard configuration

4: Control supply AC230V

2. Core Electrical Specifications

3. Ambient & Installation Conditions
4. Ambient temperature: -25℃ ~ +60℃. Derating required above 40℃; rated current reduces to 100A at 60℃
5. Installation altitude: Max 5000m. Derating required above 1000m; main circuit upper limit reduced to 460V above 2000m
6. Max cable length from soft starter to motor: 300m
7. Installation clearance: ≥100mm top, ≥5mm side, ≥75mm bottom
8. Pollution degree: 3 (IEC 60947-4-2)
9. Function Description

2-phase thyristor voltage regulation soft start, integrated bypass. Mechanical contacts carry load current during continuous operation for low power loss

Adjustable start ramp and current limit; external reset supported

Integrated equipment fault protection and motor overload protection; fault relay outputs (95/96, 95/98)

Single direction start, no braking output; no communication interface (3RW40 series without Modbus/Profinet)

Typical loads: water pumps, fans, compressors and general loads. Not suitable for frequent heavy-duty starting

5. Selection & Replacement Options
6. Factory direct upgrade model: 3RW5055-6AB14 (New 3RW5 generation)

Same rating 134A /75kW@400V, AC230V control, screw terminals; enhanced protection, optional communication module

2. Domestic alternative candidates (same current rating): Renle, Xipu, Chint, Delixi soft starters, 134A class.
3. Troubleshooting Guide (General for 3RW40 series)
4. No power-up display: Check 230V control supply and terminal wiring
5. Overload trip during startup: Verify motor rated current setting; derating required under high ambient temp or frequent start-stop
6. No torque on start: Inspect main incoming power, thyristors and bypass contacts
7. Frequent tripping: Check harmonic distortion and whether semiconductor fast fuses are fitted upstream

Comparison Table: 3RW4055-6BB44 VS 3RW5055-6AB14

3RW4055-6BB44: Discontinued legacy unit; 3RW5055-6AB14: Factory recommended replacement, screw terminal, built-in bypass, 2-phase thyristor soft starter

Replacement Implementation Key Points (Engineering Focus)

1. Primary power circuit: Fully compatible. Incoming and motor terminal positions basically match; direct replacement without re-routing power cables.
2. Secondary control circuit

Legacy unit fixed AC230V supply; new model accepts AC110~250V wide range. Existing 230V control circuit works directly.

Relay logic is similar, but new DO channels are user configurable. Verify fault/run relay logic after power-on.

New 4~20mA analog output can be left unconnected if not required.

3. Parameter re-setting: Motor rated current, start ramp and current limit must be re-programmed in new soft starter; parameters from old unit cannot be reused directly.
4. Protection scheme: Selection principle for upstream semiconductor fast fuses unchanged; retain original short-circuit protection.

Application Difference Summary

3RW4055: For existing legacy equipment, simple soft start only, no monitoring, no communication, no analog output.

3RW5055: Preferred for new projects and retrofits. Pump ramp-down recommended for pump applications. Supports communication and 4-20mA current feedback to PLC for SCADA monitoring.

1. 3RW40 (Discontinued Legacy Series｜2-phase thyristor, built-in bypass, series of target model)

Main circuit AC200~460V, built-in bypass, Class10 motor overload protection. Suffix defines terminal type, control supply and PTC option; @40℃, rated motor power at 400V.

Supplementary: Same current ratings also available with spring-cage terminals (suffix 2BBxx), 24V control supply, PTC thermistor version (TBxx). Table above lists only mainstream models with screw terminal & AC230V control supply same as 3RW4055-6BB44.

Series feature: 2-phase L1/L3 control, built-in bypass, no communication, no analog output; 3RW405~407 (S6/S12) support PTC motor thermal protection.

2. 3RW50 (New Generation Replacement Series｜Successor of 3RW40, Active Production)

Main circuit AC200~480V, built-in bypass, 2-phase thyristor, wide control supply AC110~250V; built-in 4~20mA analog output, optional Profinet/Modbus module, pump soft stop function.

Supplementary: 3RW50 same current ratings also available with spring-cage terminals (2AB14), 24V control supply and PTC version (TBxx).

3. Brief Introduction of Other Soft Starter Series in Same Family (Selection Reference)
4. 3RW30: Entry-level basic model, 2-phase, built-in bypass, low power range, no PTC, no communication; lower grade than 3RW40
5. 3RW44: Legacy high-performance type (discontinued). Supports inside-delta connection, 3-phase thyristor, rich protections, suitable for heavy duty
6. 3RW52: New generation high performance. Supports inside-delta, 3-phase thyristor, for heavy-duty fans & compressors; replacement for legacy 3RW44
7. 3RW55: High-end safety version including F safety variant, for high safety integrity applications
8. Order Number Coding Quick Reference (3RW40 / 3RW50)

Take `3RW4055-6BB44` as example

3RW: SIRIUS soft starter

40: Series code

55: Current rating code

6: Screw terminal (2 = spring-cage terminal)

BB / AB: Base hardware revision

4: Main voltage code

4: Control supply code