Skip to main content
Siemens 3RK3121-1AC00 — Safety Relays

Siemens 3RK3121-1AC00 3RK31 Central Unit, 4.5 W, IP20

MPN3RK3121-1AC00
NRND

Siemens 3RK31 central unit, order code 3RK3121-1AC00, 1/2 F-DI, 6 DI, 1 F-RO, 1 F-DO, 4.5 W, 24 V DC, screw-type terminals, IP20, 45 x 111 x 124 mm, 450 g.

$509.73Ref. price · indicative, final on quote
Sourced new & surplus through independent channelsAuthenticity-screened · ESD-safe packingListing updated Jul 2026

Specifications

3RK3121-1AC00 — Identification
ParameterValue
Product brand nameSIRIUS
Product designationCentral unit
Product design / configuration1/2 F-DI, 6 DI, 1 F-RO, 1 F-DO
3RK3121-1AC00 — Safety ratings
ParameterValue
Safety integrity level (IEC 61508)SIL CL 3
Category (EN ISO 13849-1)4
PFHd, high demand rate (EN 62061)7E-9 1/h
Hardware fault tolerance (IEC 61508)1
Stop category (EN 60204-1)0 / 1
3RK3121-1AC00 — Monitoring & inputs
ParameterValue
Emergency-off circuit monitoringYes
Protective door monitoringYes
Position switch monitoringYes
Valve monitoringYes
Monitored start-upYes
3RK3121-1AC00 — Outputs & contacts
ParameterValue
Max. operating frequency1 000 1/h
3RK3121-1AC00 — Electrical
ParameterValue
Rated insulation voltage300 V
Rated surge voltage withstand2 500 V
3RK3121-1AC00 — Connection
ParameterValue
Type of electrical connectionscrew-type terminals
Conductor cross-section, solid20 ... 14
Conductor cross-section, stranded20 ... 14
3RK3121-1AC00 — Mechanical
ParameterValue
Touch protection against electric shockfinger-safe
Fastening methodSnap-mounted to DIN rail or screw-mounted with additional push-in lug
Mounting positionvertical
Width45 mm
Height111 mm
Depth124 mm
3RK3121-1AC00 — Environmental
ParameterValue
Operating temperature range-20 ... +60 °C
Storage temperature range-40 ... +85 °C
Installation altitude, max.2 000 m
Shock resistance15g / 11 ms
Vibration resistance (IEC 60068-2-6)5 ... 500 Hz: 0.75 mm
Air pressure (SN 31205)70 ... 106 kPa

Product details

Overview

This unit is part of the 3RK31 central unit series, designed for safety-related applications with integrated emergency stop and safety circuit handling.

When equipped with the DP interface module, the unit communicates via PROFIBUS DP with 64-bit cyclical data exchange. The switching frequency is rated at 1000 operations per hour, with a minimum switching cycle of 10 operations. The shock rating of 15g for 11 ms defines the mechanical robustness for machine-mounted installations.

Snap-mounts onto DIN rail or screws to a panel with an additional push-in lug. The 45 mm width and 124 mm depth fit standard cabinet layouts. Screw-type terminals accept 20–14 AWG wire. Finger-safe touch protection is provided on the terminals. Rated IP20 for dry indoor cabinets. Maximum operating altitude 2000 m. The unit is suitable for Class A industrial EMC environments only; in residential areas it may cause radio interference requiring mitigation.

Compliance & certifications

RoHS compliant since 28-05-09. Classified for Class A industrial EMC environments. No UL or IEC certification listings documented.

MPN
3RK3121-1AC00