Siemens 3TK2821-1CB30 SIRIUS 3TK2821
The Siemens SIRIUS 3TK2821-1CB30 is a safety relay module belonging to the SIRIUS 3TK28 series, manufactured by Siemens AG. It is designed to monitor safety-critical functions such as emergency stop circuits, safety door interlocks, and two-hand control devices in industrial automation systems. The module provides reliable safety switching and is compliant with international functional safety standards.
The 3TK2821-1CB30 operates on a 24 V DC coil voltage and provides two safety-rated enabling current paths along with one auxiliary contact for signaling purposes. It achieves up to Safety Integrity Level SIL 3 per IEC 62061 and Performance Level PL e per ISO 13849-1, making it suitable for the highest safety categories. The module features guided (positively driven) contacts, automatic or manual reset options, and a compact 22.5 mm wide housing designed for DIN rail mounting.
This safety relay is widely used in machinery and plant engineering wherever personnel protection is required, including press and stamping machines, packaging lines, robotic cells, and conveyor systems. Its compact footprint and straightforward wiring make it suitable for integration into existing control cabinets across automotive, food and beverage, and general manufacturing industries.
Technical Specifications
| Series | SIRIUS 3TK28 |
|---|---|
| Input/Operating Voltage | 24 V DC |
| Safety Integrity Level | SIL 3 (IEC 62061) |
| Performance Level | PL e (ISO 13849-1) |
| Safety Category | Category 4 (EN ISO 13849-1) |
| Enabling Current Paths | 2 (safety contacts, N/O) |
| Auxiliary Contacts | 1 N/C (signaling) |
| Rated Operational Voltage | 250 V AC / 24 V DC |
| Rated Operational Current | 6 A (AC-15), 6 A (DC-13) |
| Reset Type | Automatic or manual (selectable) |
| Mounting | DIN rail (35 mm) |
| Housing Width | 22.5 mm |
| Operating Temperature | -25 °C to +60 °C |
| Protection Rating | IP40 (front), IP20 (terminals) |
| Certifications | CE, UL, cUL, TÜV |
Common Diagnostic Codes
- LED OFF (no indication)
- The safety relay is de-energized or supply voltage is absent.
Check 24 V DC supply voltage at the input terminals. Verify wiring connections and fuse integrity in the control circuit. - LED flashing (input circuit fault)
- The input monitoring circuit has detected a discrepancy or short-circuit across the safety input channels.
Inspect the emergency stop button or safety door switch wiring for cross-faults or short circuits. Ensure both input channels are correctly wired and the safety device is functioning. - Output contacts not closing
- The enabling contacts do not close after the reset signal is applied.
Verify that the reset input is correctly wired and that the reset button is being pressed after the safety circuit is restored. Check for welded contacts on the feedback loop (EDM) circuit. - Feedback loop (EDM) fault
- The external device monitoring (EDM) circuit has detected that downstream contactors or relays have not de-energized correctly.
Check the auxiliary contacts of downstream contactors wired into the EDM/feedback loop. Replace any welded or stuck contactors and verify correct wiring of the feedback circuit. - Output contacts welded
- One or more safety output contacts are welded closed due to overcurrent or short circuit.
Replace the 3TK2821 safety relay module. Investigate the cause of overcurrent in the load circuit and install appropriate fusing or protection. - Reset not effective
- The relay does not reset after the safety circuit is re-established and reset button is pressed.
Check that the safety input circuit is fully closed (emergency stop released, door closed). Verify reset wiring and confirm manual reset mode is correctly configured. Inspect for residual faults in the input circuit.
Frequently Asked Questions
What is the coil supply voltage for the 3TK2821-1CB30?
The 3TK2821-1CB30 is designed for a 24 V DC supply voltage on the control input circuit.
What safety level does the 3TK2821-1CB30 achieve?
The module achieves Safety Integrity Level SIL 3 per IEC 62061 and Performance Level PL e per ISO 13849-1, Category 4.
Does the 3TK2821-1CB30 support both automatic and manual reset?
Yes, the reset mode can be configured for either automatic or monitored manual reset depending on the application requirements.
How many safety output contacts does the 3TK2821-1CB30 provide?
The module provides two N/O safety enabling contacts and one N/C auxiliary signaling contact.
Is the 3TK2821-1CB30 compatible with two-channel emergency stop circuits?
Yes, the 3TK2821 series is designed to monitor two-channel emergency stop devices, safety door switches, and two-hand control devices in accordance with relevant machinery safety standards.
Troubleshooting
Safety relay does not energize after power is applied
Check the 24 V DC supply voltage at the A1/A2 terminals using a multimeter. Verify that the supply is within tolerance and that no fuse has blown in the control circuit.
Restore correct 24 V DC supply voltage. Replace any blown fuses and correct wiring errors at the supply terminals.
Enabling output contacts do not close after reset
Confirm that the safety input circuit (e.g., emergency stop) is fully re-established and that the reset button is being pressed. Check the EDM feedback loop for welded downstream contacts.
Release and re-engage the safety device, then press the reset button. If the EDM loop is open due to welded contacts on a downstream contactor, replace the faulty contactor and rewire the feedback circuit correctly.
Safety relay trips unexpectedly during operation
Inspect the safety input wiring for loose connections, intermittent contact faults, or electromagnetic interference causing spurious signals on the input channels.
Tighten all terminal connections, use shielded cables where appropriate, and ensure the safety input device (e.g., E-stop button) contacts are in good condition. Replace worn safety devices if necessary.
Auxiliary signaling contact does not change state
Measure continuity across the auxiliary N/C contact terminals when the relay is energized. A failed auxiliary contact or incorrect wiring may be the cause.
Verify wiring to the auxiliary contact terminals. If the contact is confirmed faulty, replace the 3TK2821 module as the contacts are not field-repairable.
Module shows signs of overheating or discoloration
Check the load current through the safety output contacts against the rated operational current. Verify that the ambient temperature inside the cabinet does not exceed 60 °C.
Reduce the load current to within rated limits, improve cabinet ventilation, and replace the module if thermal damage is evident. Install appropriately rated fusing upstream of the safety contacts.
| Condition | Repair, Used, Refurbished, New in box (sealed) |
|---|
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