What this time-relay block does and where it snaps on
The 3RT5926-2PA01 is a pneumatic time-relay block that adds an adjustable ON-delay to a Siemens 3RT5 contactor in frame sizes S2 or S3. It clips onto the front of the contactor and uses the contactor's own coil voltage — no separate power supply needed. The delay range is 0.1 to 30 seconds, set via a screwdriver-adjustable knob on the face. One normally-open and one normally-closed auxiliary contact switch after the delay expires. Wiring is through screw-type terminals on the block itself — the same tool you use for the contactor coil works here.
Fitting it to the contactor and protecting the aux contacts
This block is sized for Siemens 3RT5 contactors in frame S2 (e.g., 3RT50..) and S3 (e.g., 3RT55..). It snaps onto the front without extra hardware and adds about 20 mm to the overall depth — plan the enclosure depth accordingly. The auxiliary switch contacts need a fuse gG 10 A with a short-circuit current of 1 kA per IEC 60947-5-1. If your panel's prospective fault current at the contactor is higher than 1 kA, you'll need a current-limiting fuse upstream or a different auxiliary block.
The pneumatic mechanism is mechanical — no electronics to fail, but the bellows can stiffen in cold storage. If the block has been sitting on a shelf below 0 °C, let it warm to room temperature for an hour before adjusting the delay.