3TK2821-2CB30 Siemens Safety Relay for Emergency Stop Circuits

Product Description / Overview

The Siemens 3TK2821‑2CB30 is a compact and reliable safety relay from the SIRIUS 3TK28 series, designed to ensure machine safety in industrial automation.
It monitors emergency stop buttons, protective doors, light barriers, and other safety devices for dependable hazard prevention.

Moreover, this relay supports 24 V AC/DC supply voltage, providing flexible operation for various control circuits.
It features 3 NO enabling contacts for safety outputs and 1 NC signaling contact for feedback or diagnostics.

In addition, start-up can be configured for automatic or manual monitored operation, allowing adaptive control in different safety setups.
DIN rail mounting and cage clamp terminals simplify installation while maintaining a compact 22.5 mm housing for space efficiency.

Although this model is discontinued, Siemens recommends 3SK1111‑2AB30 or 3SK1211‑2BB40/3SK1211‑2BB00 as modern, compatible successors.

Technical Data / Specifications

Product Type: Safety relay basic unit
Series: SIRIUS 3TK28
Supply Voltage: 24 V AC/DC
Contacts: 3 NO enabling (instantaneous), 0 NO delayed, 1 NC signaling
Connection Type: Cage clamp terminals
Housing Width: 22.5 mm
Mounting: DIN rail
Protection Class: IP20
Gross Weight: 239 g
Net Weight: 0.24 kg
Packaging Dimensions (L × W × H): 106.5 × 28 × 124 mm
Operating Temperature: –25 … +60 °C
Storage Temperature: –40 … +80 °C
Relative Humidity: 10 … 95 %
Installation Altitude: Up to 2000 m
Safety Integrity Level (SIL): Up to SIL1 as basic device, SIL3 as extension unit
Performance Level (PL): Up to PL e (EN ISO 13849-1)
Standards Compliance: IEC 61508, EN ISO 13849-1, EN 62061

FAQ

What supply voltage does the 3TK2821-2CB30 require?
It operates with 24 V AC/DC, compatible with standard industrial safety circuits.

How many contacts does it provide?
It includes 3 NO enabling contacts and 1 NC signaling contact.

Can the start-up be configured?
Yes, it supports automatic or manual monitored start according to application needs.

What mounting type is used?
DIN rail mounting allows compact and secure installation in control cabinets.

Which Siemens models are recommended as successors?
3SK1111‑2AB30 or 3SK1211‑2BB40/3SK1211‑2BB00 are modern, compatible replacements.