Description

This is the Siemens SIRIUS 3RH21 contactor relay, a fundamental “logic” component for industrial control panels. While it looks like a standard motor contactor, this relay is specifically designed for switching auxiliary and control circuits where reliability and high-speed operation are key.

Core Specifications:

Contact Configuration: 2 NO + 2 NC (2 Normally Open and 2 Normally Closed). This “balanced” configuration is highly sought after for reversing logic, safety interlocks, or circuits where you need an equal number of “on” and “off” signals.

Control Supply Voltage: 24 V AC (50/60 Hz). This version is built to run directly off standard industrial control transformers.

Frame Size: S00. The smallest footprint in the SIRIUS modular system (45mm width), making it perfect for high-density DIN rail mounting.

Connection Type: Screw Terminals, providing a secure, vibration-proof connection for traditional industrial wiring.

Why Choose the 2 NO + 2 NC Layout?

Balanced Logic: The equal split of NO and NC contacts makes this model exceptionally versatile for “handshaking” between different parts of a control system—for example, signaling that one process is active (NO) while simultaneously locking out a conflicting process (NC).

Extreme Reliability: These relays are rated for millions of switching cycles, even when dealing with the low currents typical of PLC inputs or electronic sensors.

Modular Versatility: Like all SIRIUS components, you can expand it further by snapping on front-mounted auxiliary blocks if your project requirements grow.