Siemens has updated its conversion guide, which explains model by model how to migrate applications using 3TK28 relays to the SIRIUS 3SK1 range.
Anyone maintaining machines fitted with 3TK28 safety relays eventually faces the same question: which device in the current range replaces it, and how does it need to be rewired? Siemens answers this in a 123-page technical document, updated in April 2026 (version 1.10), covering the applicative conversion from 3TK28 to 3SK1.
A narrower range with more functions
According to the manufacturer, the 3SK1 Standard and Advanced series can replace every 3TK28 device, with a width of just 22.5 mm and greater functionality. The only exception is the 3TK2810 standstill and speed monitors, which remain in the catalog and are not replaced by 3SK.
The SIRIUS 3SK safety relays meet requirements up to SIL 3 (IEC 61508 / IEC 62061) and PL e (EN ISO 13849-1). The 3SK1 series is divided into two families:
- 3SK1 Standard: compact, easy-to-use and economical basic units with relay or semiconductor outputs.
- 3SK1 Advanced: multifunctional basic units with time-delayed outputs and expandable inputs and outputs. With the 3ZY1 device connector, safety functions involving several sensors and actuators can be built very quickly.
What the conversion guide includes
For each 3TK28 model, the document provides the same information:
- Cross-reference table of part numbers by supply voltage. For example, the 24 V DC 3TK2801-0DB4 is replaced by the 3SK1111-1AB30 (Standard) or the 3SK1121-1AB40 (Advanced).
- Terminal mapping between the old device and the new one.
- Side-by-side wiring diagrams for the most common applications: single-channel and two-channel emergency stop monitoring, protective door monitoring and contact expansions, including the SIL and PL achieved and the DIP switch positions.
The guide covers safety relays with relay outputs (3TK2801 to 3TK2807, 3TK2907, 3TK2820 to 3TK2828 and 3TK2830) and those with solid-state outputs (3TK2840, 3TK2841 and 3TK2842).
Points to bear in mind
For the 110 and 230 V AC versions, replacing the relay with an Advanced unit requires the 3SK1230 power module. Siemens also points out that a fuse must be fitted as short-circuit protection in both the supply line and the relay contacts of the 3SK1 devices, rated according to each device’s technical data.
Related reading: the Sirius 3RQ1 force-guided coupling relays and more machine safety news.