Siemens 3RW50746TB14 Soft Starter (480 V, 315 A, Screw Terminal)
Soft Starter Placement in the Motor Branch
The 3RW50746TB14 is a chassis-mounted solid-state soft starter designed for three-phase AC motor circuits operating at 480 V line voltage. It occupies the space between a manual motor protector or circuit breaker and the motor itself, providing controlled voltage ramp-up and ramp-down without electromechanical contactors performing the switching. The suffix "TB" in the part number denotes screw-type load and control terminals with built-in thermal overload coordination for a single AC motor up to 315 A.
The part is classified Active and carries a RoHS non-compliant designation due to the soft-start technology and chassis form factor.
Key Parameters
| Parameter | Value |
|---|---|
| Control / Drive Type | Soft Start / Stop |
| Motor Type | AC Motor (three-phase) |
| Line Voltage (load) | 480 V AC |
| Control Voltage | 110–250 V AC/DC |
| Output Current | 315 A |
| Number of Motors | 1 |
| Mounting Type | Chassis Mount |
| Operating Temperature | 25°C ~ 60°C |
| Encapsulation | Box |
| RoHS Compliance | Non-compliant |
Control Voltage Context
The stated control voltage range of 110–250 V AC/DC accommodates standard industrial control circuits. This means the start/stop command signals and any feedback wiring can use common 120 V or 230 V control levels found in panel cabinets without requiring an additional control power supply converter.
Selection Trade-offs for 3RW50 "TB" vs. "AB" Variants
The in-catalog variants of the 3RW50746 share identical current, voltage, motor type, mounting, and thermal operating range. The primary selection dimensions are:
- Screw ("TB") vs. Spring ("AB") terminals: "TB" variants use screw clamp terminations, which are suitable for larger conductor sizes typical of 315 A branch wiring and allow for field re termination without special tooling. "AB" variants use spring-cage terminations, which can reduce wiring time but may impose stricter conductor specifications.
- 480 V vs. 600 V line voltage: All "TB" variants are offered at either 480 V or 600 V load voltage ratings. The catalog listing for the primary part indicates 480 V; selecting a 600 V variant requires choosing from the alternates if that rating is needed.
- 110–250 V vs. 24 V control voltage: The "TB" suffix with 110–250 V control voltage is shown in the primary record. The alternates include 24 V control voltage variants (3RW50746TB04, 3RW50746TB05) which require a separate 24 V DC control supply — a consideration when wiring into existing control architectures.
Similar Catalog Parts
The comparison below lists in-catalog parts sharing identical key parameters (control type, motor type, mounting, encapsulation, current rating). All require the reader's own engineering qualification before use.
| MPN | Line Voltage | Control Voltage | Similarity (0–1) |
|---|---|---|---|
| 3RW50746TB14 (primary) | 480 V | 110–250 V | — |
| 3RW50746TB15 | 600 V | 110–250 V | 1.00 |
| 3RW50746TB04 | 480 V | 24 V DC | 1.00 |
| 3RW50746TB05 | 600 V | 24 V DC | 1.00 |
| 3RW50746AB14 | 480 V | 110–250 V | 0.92 |
| 3RW50746AB15 | 600 V | 110–250 V | 0.92 |
3RW50746TB15 differs in rated line voltage (600 V vs. 480 V), which extends its suitability to higher-voltage installations; the control voltage range and current rating remain identical.
3RW50746TB04 reduces the control voltage requirement to 24 V DC, eliminating compatibility with 120 V control circuits but simplifying integration in low-voltage control architectures.
3RW50746AB14 shares the 480 V line voltage and 110–250 V control voltage range but substitutes spring-cage ("AB") for screw ("TB") terminals — a terminal-type difference rather than an electrical or performance difference.
No in-catalog alternates are listed outside the nine MPNs confirmed in the seed and alternates.
FAQ
What motor ratings does the 3RW50746TB14 support? The part is rated for a single three-phase AC motor at 480 V line voltage with a maximum output current of 315 A. Exact motor horsepower compatibility depends on the specific motor nameplate and coordination with upstream short-circuit protection — the catalog record does not state a horsepower value.
Can the 3RW50746TB15 be substituted for the 3RW50746TB14? The 3RW50746TB15 carries a higher rated line voltage (600 V vs. 480 V) while matching the current rating and control voltage range. Substituting it at 480 V requires the reader's own engineering qualification to confirm that the higher voltage rating does not impose any installation or coordination constraints in the specific circuit.
Is the thermal overload function built into the 3RW50746TB14? The title string includes "THERM" and the part designation carries the "TB" suffix, which in the Siemens 3RW50 family denotes screw terminal variants with integrated thermal overload coordination for the connected motor. Specific thermal trip settings and coordination class (such as Class 10 or Class 20) are not stated in the catalog record.