5SY4350-8 - 50A 3-Pole D-Curve MCB 10kA 400V | Siemens
MPN: 5SY4350-8 ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $248.5 | $248.50 |
| 5 | $235.1 | $1,175.50 |
| 10 | $221.8 | $2,218.00 |
| 25 | $208.4 | $5,210.00 |
| 50 | $195 | $9,750.00 |
5SY4350-8 Overview
A miniature circuit breaker (MCB) is a thermo-magnetic protective device designed to automatically interrupt an electrical circuit on overload or short-circuit conditions, and it is the fundamental building block of low-voltage power distribution. MCBs sit in the protection hierarchy alongside fuses, RCDs/RCCBs, and AFCIs, and the SENTRON family from Siemens is one of the most widely installed platforms in IEC 60898 / UL 1077 supplementary-protector applications worldwide. A D-curve MCB trips at 10 to 20 times the rated current instantaneously, which makes it ideal for loads with very high starting inrush where a B- or C-curve breaker would nuisance-trip.
Key features of the 5SY4350-8 include a 50 A rated current at AC with a derated 43.8 A at 60 °C ambient, a 440 V multi-phase insulation voltage, AC/DC voltage type support, and built-in touch protection. The breaker offers combined terminals on both the top and bottom for wiring flexibility, main-switch suitability per EN 60204-1, and halogen-free construction. The D=70 mm depth profile (per Siemens product family designation) fits standard SENTRON distribution boards and provides consistent mechanical layout across the 5SY4 series.
Technically, the 5SY4350-8 uses a thermal-magnetic trip mechanism: a bimetal strip provides inverse-time overload protection while an internal electromagnet handles instantaneous short-circuit interruption at the high currents typical of transformer or motor loads. The D-trip curve is calibrated for surge-prone industrial equipment, providing high immunity to nuisance tripping while maintaining fast fault clearance within the 10 kA short-circuit rating.
Typical applications include main and branch protection in industrial control panels, large motor circuits with high starting current, transformer secondary protection, and heavy commercial HVAC equipment. Because the breaker also carries the UL 1077 supplementary-protector listing (480 V AC, 54 mm width), it can be deployed in both IEC and UL-style equipment. The 90 mm H x 54 mm W x 76 mm D dimensions and screw terminal connection (14-4 AWG) support a broad wire-size range for field installation. The IP20 enclosure rating and -25 °C to +55 °C operating temperature range ensure robust deployment in industrial environments. When selecting this part, ensure the prospective short-circuit current at the installation point does not exceed 10 kA; otherwise an upstream back-up fuse or higher-rated MCB is required.
Drop-in alternatives for 5SY4350-8 — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
5SY4350-7
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
5SY4351-8
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
5SY4350-6
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
A9F79350
✅ Drop-In📋 Reference alternative (not in catalog)
PLSM-D50/3
✅ Drop-In📋 Reference alternative (not in catalog)
5SY4350-8 Specifications
| Number of Poles | 3 |
| Rated Current (In) | 50 A |
| Rated Current at 60 °C | 43.8 A |
| Rated Voltage (AC) | 400 V |
| Rated Voltage (UL 1077) | 480 V AC |
| Insulation Voltage (multi-phase AC) | 440 V |
| Rated Short-Circuit Capacity (Icn) | 10 kA at 400 V AC |
| Tripping Characteristic | Class D |
| Voltage Type | AC / DC |
| Mechanical Service Life | 10,000 operating cycles (typical) |
| Overvoltage Category | 3 |
| Degree of Pollution | 3 |
| Mounting | 35 mm DIN Rail |
| Connection Type | Screw terminal (combined top/bottom) |
| Wire Range | 14 to 4 AWG |
| Touch Protection | Yes (IP20) |
| Halogen Free | Yes |
| Main Switch Suitability (EN 60204-1) | Yes |
| Neutral Conductor Switching | No |
| Operating Temperature | -25 °C to +55 °C |
| Dimensions (H x W x D) | 90 mm x 54 mm x 76 mm (per Standard Electric Supply) |
| Width (per Pole Module) | D=70 mm (Siemens product family designation) |
| UL File Reference | UL File E116386 Vol. 1 Sec. 2 |
| Standard | IEC 60898 / UL 1077 |
| RoHS Status | Compliant |
5SY4350-8 standard Pin Configuration Guide
Pin configuration for 5SY4350-8 (standard package). Pin numbering, functions, and connection diagrams are defined in the manufacturer datasheet. Refer to it for the exact footprint and soldering guidelines.
No detailed pinout data available for 5SY4350-8.
Refer to the datasheet for full pin configuration.
Typical Applications
5SY4350-8 is suitable for 6 applications: Industrial Motor Branch Protection, Transformer Secondary Protection, HVAC Heavy Commercial Equipment, Welding Equipment Branch Circuits, Industrial Distribution Board Main, Backup Power UPS Output Distribution.
Industrial Motor Branch Protection
The 5SY4350-8 protects three-phase induction motor branch circuits up to approximately 25 hp at 400 V AC. Its D-tripping characteristic (instantaneous at 10-20x In) tolerates the 6-8x locked-rotor inrush typical of large AC motors without nuisance tripping, while its 10 kA Icn at 400 V handles motor contribution to fault current. The 35 mm DIN-rail mounting and combined top/bottom screw terminals support 14-4 AWG conductors, matching the wire range typically required for motor feeders. Coordination with an IEC 60947-4-1 contactor and thermal overload relay delivers full Type-2 protection per IEC 60269 in motor control centers.
Recommended
Transformer Secondary Protection
The 5SY4350-8 is well-matched to 50 kVA three-phase control transformer secondary protection on 400 V AC distribution boards. Its D-curve accommodates the 8-15x inrush typical of transformer magnetizing currents during energization, while its 10 kA interrupt rating clears secondary-side short circuits before upstream back-up protection operates. The -25 to +55 °C operating envelope and 43.8 A derating at 60 °C support deployment in unconditioned industrial cabinets without thermal management. The halogen-free construction and EN 60204-1 main-switch rating make it suitable for machinery main-disconnect per IEC/EN 60204.
Recommended
HVAC Heavy Commercial Equipment
The 5SY4350-8 protects large commercial HVAC compressor and fan motor circuits from 20-25 hp at 400 V AC. The D-curve tolerates the locked-rotor inrush of scroll and screw compressors during startup, while the 480 V AC UL 1077 supplementary-protector listing allows deployment in North American unitary equipment alongside IEC-style distribution gear. Touch-safe IP20 combined terminals and 35 mm DIN-rail mounting simplify integration into packaged HVAC control panels. The 10,000-cycle mechanical service life supports the frequent switching required by duty-cycled refrigeration compressors.
Recommended
Welding Equipment Branch Circuits
The 5SY4350-8 protects dedicated 50 A branch circuits feeding inverter-based welding equipment and resistance welding transformers where high inrush is normal. The D-curve instantaneous trip threshold of 500-1000 A tolerates the IGBT-capacitor charge currents typical of welding inverter front-ends without nuisance tripping. The 10 kA Icn at 400 V AC handles the limited short-circuit current of upstream welding transformers and isolation supplies. The combined-terminal design accepts the larger 6-4 AWG conductors typically required to limit voltage drop on long welding drop cables.
Recommended
Industrial Distribution Board Main
The 5SY4350-8 serves as a 50 A three-pole main disconnect in sub-distribution boards feeding smaller 16-32 A subcircuits. With its EN 60204-1 main-switch suitability rating, it can be used as the marked disconnecting means for industrial machinery per EU machinery directive. The 90 mm H x 54 mm W x 76 mm D footprint and DIN-rail mount integrate into standard SENTRON-compatible enclosures. The 440 V multi-phase insulation voltage supports 400 V AC nominal systems with typical 10% transient overvoltages from utility switching and capacitor switching events.
Recommended
Backup Power UPS Output Distribution
The 5SY4350-8 protects three-phase UPS output distribution feeders supplying industrial control loads, where the D-curve handles the high inrush of ferroresonant transformers and DC-link capacitor charging during UPS restart events. The AC/DC voltage type rating handles the mixed waveform content present at UPS outputs feeding non-linear rectifier loads. The 35 mm DIN-rail mount supports retrofit deployment in UPS output cabinets, while the halogen-free construction suits environmentally sensitive sites. The 10 kA interrupt rating provides fault coverage typical of UPS-limited short-circuit currents.
Recommended
Recommended Products Summary
Engineering reference data for 5SY4350-8 — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | 5SY4350-7 | 5SY4351-8 | 5SY4350-6 | A9F79350 | PLSM-D50/3 |
|---|---|---|---|---|---|---|
| Brand | Siemens | Siemens | Siemens | Siemens | Schneider Electric | Eaton |
| Package | 5SY4 DIN-rail module (D=70 mm, 35 mm rail) | 5SY4 DIN-rail module - same | 5SY4 DIN-rail module - same | 5SY4 DIN-rail module - same | iC60H DIN-rail module - 18 mm pitch (vs Siemens 17.5 mm) | PLSM DIN-rail module - 17.5 mm pitch |
| Rated Current (In) | 50 A | 50 A | 51 A (+2%) | 50 A | 50 A | 50 A |
| Tripping Characteristic | Class D (10-20x In) | Class D | Class D | Class D | Class D | Class D |
| Number of Poles | 3P | 3P | 3P | 3P | 3P | 3P |
| Rated Voltage (AC) | 400 V | 400 V | 400 V | 400 V | 400 V | 400 V |
| Short-Circuit Capacity (Icn) | 10 kA | 10 kA | 10 kA | 6 kA (-40%) | 10 kA | 10 kA |
| UL 1077 Listed | Yes (480 V AC, UL E116386) | No (IEC-only) | Yes | No (IEC-only) | Yes (UL 489 alternative listings) | Yes (UL 489) |
| Mechanical Service Life | 10,000 cycles | 10,000 cycles | 10,000 cycles | 10,000 cycles | 10,000 cycles | 10,000 cycles |
| Operating Temperature | -25 to +55 °C | -25 to +55 °C | -25 to +55 °C | -25 to +55 °C | -25 to +60 °C | -25 to +55 °C |
Key Differentiators
- Dual IEC 60898 and UL 1077 certification in a single part number (vs 5SY4350-7)
- Higher 10 kA short-circuit rating vs lower-interrupt alternate (vs 5SY4350-6)
- Siemens SENTRON 5SY4 family ecosystem with broad accessory support (vs Schneider Electric A9F79350)
Design Notes
Estimated: At 50 A continuous load in a fully populated 5SY4 distribution board with 30 K temperature rise, the breaker derates from 50 A to approximately 43.8 A at 60 °C per the Siemens datasheet. For installation in unconditioned industrial cabinets exceeding 50 °C ambient, apply the published 0.6-0.8 In derating factor or use a 63 A breaker to maintain 50 A continuous capacity.
Confirm the prospective short-circuit current at the breaker terminals does not exceed 10 kA. The D-trip curve provides instantaneous tripping at 500-1000 A (10-20x In), which may nuisance-trip sensitive electronic loads - for variable-frequency drives or DC power supplies, use a C-curve breaker instead. Verify wire range compatibility: the combined terminals accept 14-4 AWG; for larger conductors use a terminal adapter.
Mount the 5SY4350-8 on a 35 mm DIN rail with adequate heat dissipation space above and below - Siemens recommends at least 10 mm of free air around the device at the rated current. For multi-pole installations, derate by 0.8 (3P) or 0.9 (2P) when devices are stacked without ventilation gaps. Use the Siemens busbar system for parallel-pole configurations rather than individual wiring.
Per EN 60204-1, when using the 5SY4350-8 as a main disconnect, install a padlockable handle lockout accessory and clearly label the device with its disconnecting function. The touch-safe IP20 combined terminals allow safe operation without additional shrouding. Ensure the upstream supply is de-energized and locked-out before any service work on the breaker or downstream circuits.
The 5SY4350-8 is NOT a substitute for a fuse or molded-case circuit breaker on circuits exceeding 10 kA prospective fault current - it is rated for IEC 60898 / UL 1077 supplementary-protector duty. For branch-circuit protection per UL 489 or IEC 60947-2 with higher interrupt ratings, select a Siemens 3VA molded-case breaker or Eaton PLSM-D50/3 UL 489-listed alternative.
Compliance Information
RoHS and REACH compliant per Siemens SENTRON product family certification. Halogen-free construction confirmed by datasheet. UL 1077 supplementary-protector listed under File E116386 (480 V AC). EN 60204-1 main-switch suitability rated. Not AEC-Q100 qualified - circuit breakers are not automotive-grade semiconductor components.
