Description
Siemens 3RW4073-6BB44 SIRIUS Soft Starter
Product Overview
The Siemens 3RW4073-6BB44 is a high-current member of the SIRIUS 3RW40 soft-starter family, designed to reduce the electrical and mechanical stresses associated with starting three-phase AC motors. This S12-size unit is rated for 230 A at 40°C and supports standard-circuit motor applications from 200 to 460 V AC. At 400 V and 40°C, Siemens specifies a motor output rating of 132 kW. The starter uses thyristor power electronics during the starting and stopping process and incorporates an integrated bypass contact system for normal running operation.
In a motor-control cabinet, the Siemens 3RW4073-6BB44 sits between the incoming motor supply and the motor rather than acting as a PLC or variable-frequency drive. Its job is controlled acceleration and deceleration, with adjustable current limiting and integrated motor-overload protection. Siemens specifies 230 V AC control power for this particular MLFB. The device also provides external reset capability and intrinsic device protection.
For legacy motor-control installations, the exact MLFB matters. Siemens has classified this particular 3RW40 device as phased out and identifies the SIRIUS 3RW5073-6AB14 as its preferred successor. That does not mean the newer 3RW5 unit should be substituted without engineering review: cabinet dimensions, terminals, control wiring, protection behavior, parameterization, and application requirements must all be checked before migration.
Product Introduction — Non-Templated
Large motors do not need full-voltage starting every time the process starts. The 3RW4073-6BB44 uses controlled semiconductor switching to manage motor acceleration, reducing the starting-current and mechanical shock associated with direct-on-line starting. With a 230 A rating, this is intended for substantially larger motors than the smaller 3RW40 frame sizes.
For a legacy motor-control replacement, the 230 A rating and 230 V AC control supply are two of the first details to verify. The unit is no longer a current Siemens product, so remaining-stock procurement and migration to the 3RW5 family should be evaluated separately.
Key Technical Specifications
| Parameter | Specification |
|---|---|
| Product Model | 3RW4073-6BB44 |
| Manufacturer | Siemens |
| Product Family | SIRIUS 3RW40 |
| Product Type | Soft starter |
| Size | S12 |
| Rated Operating Current | 230 A at 40°C |
| Rated Operating Current at 50°C | 205 A |
| Rated Operating Current at 60°C | 180 A |
| Standard Operating Voltage | 200–460 V AC |
| Rated Motor Power at 230 V | 75 kW at 40°C |
| Rated Motor Power at 400 V | 132 kW at 40°C |
| Motor Power at 200/208 V | 60 hp at 50°C |
| Control Supply | 230 V AC |
| Control Voltage Frequency | 50/60 Hz |
| Operating Frequency | 50–60 Hz |
| Frequency Tolerance | -10% relative |
| Main Switching Technology | Thyristors |
| Integrated Bypass | Yes |
| Motor Overload Protection | Yes |
| Adjustable Current Limiting | Yes |
| External Reset | Yes |
| Motor Thermistor Evaluation | No |
| Motor Brake Output | No |
| Insulation Voltage | 600 V |
| Pollution Degree | 3 according to IEC 60947-4-2 |
| Protection Rating | IP00 |
| Auxiliary Contacts | 2 NO + 1 changeover |
| Main Terminals | Screw/box terminal arrangement |
| Dimensions | Approximately 160 × 230 × 278 mm |
| Weight | Approximately 8.695 kg |
| Lifecycle | Phased out |
| Preferred Successor | 3RW5073-6AB14 |
Siemens specifies thermal derating with ambient temperature: the 230 A rating applies at 40°C, decreasing to 205 A at 50°C and 180 A at 60°C. That rating difference should be considered when checking an existing enclosure rather than simply matching the motor’s nameplate current.
3RW4073 6BB44
Major Features / Practical Advantages
High-Current S12 Soft Starter
The 3RW4073-6BB44 belongs to the S12 size of the SIRIUS 3RW40 family and is rated at 230 A under the specified 40°C conditions. Siemens assigns it a 132 kW motor rating at 400 V in the standard circuit.
That makes this a serious motor-control device rather than a small auxiliary starter. At this current level, cable sizing, cabinet heat dissipation, upstream protection, motor starting characteristics, and installation clearances all deserve review during replacement.
Thyristor-Based Starting
During motor acceleration, the soft starter controls the applied voltage through thyristor switching. Instead of immediately applying full line voltage as a conventional direct-on-line starter does, the controller manages the starting process.
The practical objective is controlled motor acceleration with lower starting stress. The exact improvement in starting current depends on the programmed ramp, current-limit settings, motor characteristics, and load torque. It should not be expressed as a fixed percentage without those parameters.
Integrated Bypass Contact System
The 3RW4073-6BB44 includes an integrated bypass contact system. Once the motor reaches normal running conditions, the bypass arrangement reduces the time the power semiconductors remain in the main current path. Siemens explicitly lists the integrated bypass contact system as part of this model.
This is useful in high-current applications because semiconductor conduction losses are not treated as if the thyristors must carry the full continuous motor current indefinitely.
Adjustable Current Limiting
The device provides adjustable current limiting. This allows the commissioning engineer to control the maximum starting current rather than relying only on a fixed voltage ramp. Siemens identifies adjustable current limitation as an integrated product function.
For high-inertia loads, this setting needs to be coordinated with the motor’s acceleration time. An aggressively low current limit can simply leave a large motor sitting in the acceleration region for too long.
Integrated Motor Overload Protection
Siemens identifies motor overload protection as an integrated function. This reduces the need to treat the soft starter as nothing more than a semiconductor switching block.
Still, the overload setting must correspond to the actual motor and application. The soft starter should not be assumed to reproduce every protection function of a dedicated electronic motor-management relay.
Temperature Derating
At 40°C, the rated operating current is 230 A. Siemens reduces this to 205 A at 50°C and 180 A at 60°C.
This is an important field detail. A 230 A nameplate does not mean 230 A is continuously available at every cabinet temperature. For an existing installation operating in a hot MCC or poorly ventilated enclosure, the thermal environment may be the limiting factor.
Heavy-Duty Main Termination
The main current circuit uses large conductor cross-sections appropriate for the 230 A class. Siemens documentation gives conductor ranges extending into the hundreds of square millimeters, depending on conductor construction and the particular clamping point.
During replacement, do not assume the existing cable can simply be transferred without checking the terminal arrangement. Cable lug geometry, conductor size, bending radius, torque, and access space can all become practical constraints.
Legacy Replacement Status
Siemens explicitly identifies the 3RW4073-6BB44 as phased out and names the 3RW5073-6AB14 as its preferred successor.
For an operating plant, this creates two different procurement paths:
- Like-for-like maintenance: source the exact 3RW4073-6BB44 and verify condition, revision, and testing.
- Lifecycle migration: evaluate the 3RW5073-6AB14 and engineer the replacement as a system change.
Those are not the same job. A newer soft starter may be technically preferable for lifecycle reasons while still requiring wiring, parameter, enclosure, and commissioning changes.
Related Products
- Siemens 3RW4072-6BB44 — Smaller 3RW40 S12-class soft starter with lower current capability; application selection depends on motor current and thermal conditions.
- Siemens 3RW4074-6BB44 — Higher-current 3RW40 family variant; useful where the motor exceeds the 3RW4073 current class.
- Siemens 3RW4076-6BB44 — Larger 3RW40 S12 soft starter rated at 432 A and 250 kW at 400 V under the specified conditions. Siemens also lists this model as phased out.
- Siemens 3RW5073-6AB14 — Siemens’ preferred successor identified for the 3RW4073-6BB44. It belongs to the newer SIRIUS 3RW5 generation and should be evaluated as a migration rather than assumed to be a drop-in spare.
- Siemens 3RW5076-6AB14 — Preferred successor associated with the larger 3RW4076-6BB44. Useful as a reference when comparing the higher-current 3RW40 family.
- Siemens SIRIUS 3RW40 Series — The broader soft-starter family covering multiple current and power classes for three-phase motor starting.
- Siemens SIRIUS 3RW5 Series — Newer soft-starter generation intended to replace phased-out 3RW40 products in many applications.
The related models should be selected according to motor current, motor power, starting method, ambient temperature, circuit configuration, and required control features—not merely physical size.
Frequently Asked Questions
What is Siemens 3RW4073-6BB44?
It is a SIRIUS 3RW40 S12 soft starter rated at 230 A at 40°C, designed for three-phase AC motor starting and stopping. Siemens specifies 200–460 V AC operating voltage and 132 kW at 400 V under standard 40°C conditions.
Can I use it on a 132 kW, 400 V motor?
That is the published standard-circuit rating: Siemens specifies 132 kW at 400 V and 40°C. Actual suitability still requires checking the motor’s rated current, starting characteristics, load torque, duty cycle, ambient temperature, and applicable starting class.
Can I hot-swap the 3RW4073-6BB44?
Do not treat it as an unrestricted hot-swappable device. It is installed directly in a high-current motor power circuit. Replacement should be performed with the appropriate electrical isolation, lockout/tagout, discharge verification, and motor-control maintenance procedure.
Does this model support 24 VDC control power?
No. The exact 3RW4073-6BB44 specifies a 230 V AC control supply. Do not substitute a similarly named 3RW40 model with a different control-voltage suffix without checking the complete MLFB.
Does it have an integrated bypass?
Yes. Siemens specifies an integrated bypass contact system.
Does the 3RW4073-6BB44 support motor thermistor evaluation?
No. Siemens’ technical data explicitly list motor thermistor protection evaluation as not provided for this model.
Is the 3RW4073-6BB44 still a current Siemens product?
No. Siemens’ Industry Mall identifies it as a phased-out product and specifies 3RW5073-6AB14 as the preferred successor.
Does the model support firmware v3.1?
Do not infer a firmware version from this MLFB. The 3RW40 is a legacy soft-starter platform, and the exact firmware/revision should be established from the installed device or its documentation if firmware compatibility is relevant.
Can I replace it directly with 3RW5073-6AB14?
Not without an engineering check. Siemens identifies 3RW5073-6AB14 as the preferred successor, but a successor is not automatically a wire-for-wire replacement. Compare control voltage, terminals, dimensions, motor data, starting parameters, auxiliary contacts, protection functions, and cabinet requirements before migration.
Can a New Surplus 3RW4073-6BB44 be used as a maintenance spare?
Yes, provided the exact MLFB is confirmed and the unit passes appropriate inspection/testing. Because Siemens has phased out this model, verify the nameplate, terminal condition, insulation/functional test results, storage condition, and any available manufacturing/revision information before installation.
Procurement Note
For Siemens 3RW4073-6BB44, the procurement specification should explicitly state:
- Exact MLFB: 3RW4073-6BB44.
- SIRIUS 3RW40 / S12 family.
- 230 A rated operating current at 40°C.
- 200–460 V AC motor circuit.
- 230 V AC control supply.
- 132 kW at 400 V, 40°C, standard circuit.
- Integrated bypass contact system.
- Screw/box terminal arrangement.
- Required ambient-temperature derating.
- Exact auxiliary-contact requirements.
- Physical dimensions and cabinet clearance.
- Replacement versus migration requirement.
The temperature rating deserves special attention. The same unit is rated at 230 A at 40°C, 205 A at 50°C, and 180 A at 60°C. That can materially affect an MCC application where the cabinet environment runs hot.
For a legacy installation, the safest like-for-like purchase remains the exact 3RW4073-6BB44. For lifecycle planning, Siemens’ documented preferred successor is 3RW5073-6AB14, but that should be handled as an engineered migration rather than an assumption of direct interchangeability.
