The Siemens 6EP1333-2BA20 is a compact SITOP PSU100S stabilized power supply engineered to deliver regulated 24 V DC at 5 A for industrial automation and control systems. In modern control cabinets, 24 V DC is the “common language” shared by PLCs, distributed I/O, sensors, relays, industrial communication devices, and many small actuators. The job of the PSU is not simply to output 24 V in a lab, but to keep that voltage stable when loads switch, lines dip, cabinets heat up, and maintenance work introduces the occasional wiring surprise. The PSU100S platform is designed for that reality with automatic AC input range selection, adjustable output voltage, robust protection functions, and simple status/diagnostic signaling.
Unlike oversized power units that are optimized for very high currents, the 6EP1333-2BA20 focuses on the most common control-power sweet spot: dependable 24 V power for small-to-medium loads, with enough reserve behavior to handle inrush events and short overloads without turning every cabinet hiccup into a full system reset. It also emphasizes practical installation: DIN-rail mounting, screw terminals, and clear guidance for upstream protection and cabinet spacing.
Key Technical Specifications (Summary Table)
| Item | Specification |
|---|---|
| Product / Family | Siemens SITOP PSU100S |
| Part number | 6EP1333-2BA20 |
| Input type | 1-phase AC |
| AC input selection | Automatic range selection |
| AC input ranges | 85–132 V AC or 170–264 V AC |
| Line frequency | 47–63 Hz (50/60 Hz nominal) |
| Inrush current limit | max 40 A at 25 °C |
| Output | Controlled, isolated DC voltage |
| Rated output voltage | 24 V DC |
| Output adjustment | 22.8–28 V (potentiometer) |
| Rated output current | 5 A |
| Output current capability | 0–6 A; 6 A up to +45 °C (derating above) |
| Typical output power | 144 W |
| Efficiency | 88% |
| Hold-up time | min 20 ms at rated current (specified conditions) |
| Ripple | typical 30 mV, max 150 mV |
| Status indication | Green LED “24 V OK” |
| Signaling output | Relay NO contact “24 V OK”, 60 V DC / 0.3 A |
| Protection | Short-circuit proof, constant current characteristic; current limitation 6–7.1 A |
| Overload capability | 150% Iout rated up to 5 s/min |
| Overvoltage protection | Vout < 33 V (internal fault protection) |
| Operating temperature | -25 to +70 °C (natural convection) |
| Protection class | IP20 |
| Mounting | DIN rail EN 60715 (35×7.5/15), snap-on |
| Dimensions (W×H×D) | 50 × 125 × 120 mm |
| Net weight | 0.39 kg (datasheet) |
| Reliability | MTBF at 40 °C: 1,998,441 h |
What the 6EP1333-2BA20 delivers in real installations
Automatic input range selection for mixed mains environments
A common pain point in global machine builds is handling different mains conditions cleanly. The 6EP1333-2BA20 supports 120/230 V AC nominal input with automatic range selection, and it specifies two operating input ranges: 85–132 V AC and 170–264 V AC.
This reduces commissioning risk because the PSU is designed to adapt across standard single-phase mains ranges without requiring manual range switching.
Adjustable 24 V output for cabinet voltage drop management
In cabinets with long 24 V runs or higher distributed current, voltage drop can accumulate across wiring, terminal blocks, fusing, and connectors. This unit supports output adjustment from 22.8 to 28 V via a potentiometer.
That allows the integrator to compensate for predictable distribution losses so that end devices still see a stable voltage, while staying within the allowable input limits of connected equipment.
Fast response and controlled startup behavior
The datasheet describes short setting times (typically 1 ms on load steps 10→90% and 90→10%) and limits output overshoot at power-up (Vout overshoot < 3%).
For automation systems, that combination matters: fast recovery helps prevent communication brownouts during load changes, and controlled startup reduces nuisance trips or unpredictable behavior in sensitive electronics.
Protection, overload handling, and fault behavior
The 6EP1333-2BA20 is specified as short-circuit proof and uses a constant current characteristic, with a current limitation response range of 6 to 7.1 A and a typical enduring short-circuit current of 7.1 A RMS. This is a practical protection style for control circuits: it limits current during faults while allowing the system to recover once the fault is removed.
For non-fault overload events, the PSU supports 150% of rated output current up to 5 seconds per minute. That’s useful for brief peaks such as valve manifold actuation, relay energizing, or device startup surges that exceed steady-state current but do not represent a true fault condition.
Overvoltage protection is also specified for internal fault conditions with Vout < 33 V. This helps protect downstream devices from damaging overvoltage events inside the supply itself.
Monitoring and diagnostics integration
On the front of the unit, a green LED “24 V OK” provides immediate confirmation of healthy output voltage. For cabinet-level monitoring, the PSU includes a relay “24 V OK” signaling contact (NO contact, rated 60 V DC / 0.3 A).
That relay contact can be wired to a PLC input or alarm system so the control logic can detect “power good” status explicitly instead of inferring it from symptoms such as I/O dropouts.
Installation considerations: wiring, spacing, and upstream protection
The unit uses screw terminals for both input and output connections, with conductor ranges specified for input (L, N, PE) and output (+, −), and additional terminals for signaling/alarm contacts. Mechanically, it snaps onto DIN rail EN 60715 and supports lineup mounting in cabinets.
Siemens also specifies recommended cabinet clearances: 50 mm top and 50 mm bottom with natural convection. Respecting these clearances is one of the simplest ways to protect long-term reliability, especially in warm cabinets or when multiple heat sources sit adjacent.
For upstream protection, the datasheet recommends a miniature circuit breaker starting from 6 A, characteristic C, and it specifies inrush current limitation behavior (max 40 A at 25 °C). Proper upstream protection coordination helps reduce nuisance tripping while maintaining safe fault clearing.
Standards, approvals, and long-term reliability signals
For industrial deployments, compliance is not a checkbox; it is often a requirement for machine acceptance. The datasheet lists approvals such as CE, cULus (UL 508 / CSA C22.2 No. 107.1), UKCA, and EAC, along with EMC references such as EN 55022 Class B and immunity standard EN 61000-6-2.
Reliability is supported by the published MTBF at 40 °C of 1,998,441 hours. While MTBF is not a guarantee of lifetime, it is a meaningful comparative indicator when selecting PSUs for continuous industrial operation.
Recommended applications
The 6EP1333-2BA20 is a strong choice for:
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PLC and distributed I/O supply in compact automation cabinets
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24 V DC power for industrial communication devices (switches, gateways, fieldbus modules)
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Sensor groups, small actuator controls, and relay/control logic circuits
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Machine retrofits where stable 24 V and DIN-rail installation are required
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Systems needing a practical “power good” relay signal to the controller
Conclusion
The Siemens 6EP1333-2BA20 combines the essentials of an industrial 24 V PSU—stable 24 V / 5 A output, automatic AC input range selection, adjustable output voltage, robust short-circuit and overload handling, and straightforward cabinet integration—into a compact SITOP PSU100S form factor. For OEMs and maintenance teams who want predictable cabinet power behavior without overcomplicating the design, this model delivers a clean balance of performance, protection, and practical diagnostics.
