ABB  REA101-AAA Auxiliary Relay Module – Reliable Signal Isolation for Industrial Control Systems

The Siemens REA101-AAA is a compact auxiliary relay module typically used in industrial automation panels where signal amplification or circuit isolation is needed. From my experience, it’s commonly found in motor control centers, pump stations, and low-voltage switchgear setups—especially when you’re dealing with PLC output expansion or interposing between sensitive controls and high-load devices.

Key Features

• 6-Pole Changeover Contacts: Offers multiple contact paths, which seems ideal when branching one control signal to several circuits—like triggering alarms, status indicators, and interlocks simultaneously.
• 24 VDC Coil Voltage: Designed to interface directly with most PLC digital outputs without needing additional voltage conversion stages.
• Plug-in Design with Test Button: One thing I appreciate is the front-mounted test button—it allows field technicians to simulate operation during commissioning or troubleshooting without manipulating the actual control signal.
• LED Status Indication: Clear visual feedback on coil energization; helps reduce downtime during diagnostics.
• DIN Rail Mountable (35 mm): Fits standard control cabinets, and swaps are quick if replacement is ever needed.

Technical Specifications

Application Fields

In many cases, the REA101-AAA shows up in building management systems—particularly HVAC controls—where a single BMS output might need to trigger a damper actuator, fan starter, and alarm contact all at once. It’s also used in water treatment plants for isolating SCADA signals from motor loads, reducing electrical noise feedback into control logic. You might notice that it’s especially common in retrofit projects where legacy electromechanical relays are being replaced but full PLC upgrades aren’t budgeted.

Advantages & Value

While not the smallest relay available, its robust contact rating means fewer derating concerns under real-world load conditions. Procurement teams tend to favor this model due to Siemens’ long-term part availability and compatibility across Sirius series components. The plug-in design also reduces wiring errors during panel assembly, which can cut commissioning time by a noticeable margin—especially on large job sites with multiple electricians.

Installation & Maintenance

Install in a clean, dry enclosure meeting IP54 or higher standards. Ensure adequate ventilation around the relay base—continuous ambient temperatures above 50°C may shorten lifespan. Wiring should use 0.75–1.5 mm² stranded conductors with ferrules, torqued to 0.6 Nm. One practical tip: label both the relay and its corresponding terminal block since they can be swapped easily during maintenance. No scheduled calibration is required, but periodic visual inspection for discoloration or arcing signs is recommended—especially in dusty environments.

Quality & Certifications

Certified to CE, UL 508, and RoHS standards. The unit is designed and tested according to IEC 61810-1, ensuring reliable performance in industrial environments. Comes with a 365-day warranty against manufacturing defects. Firmware updates aren’t applicable—this is an electromechanical device—but Siemens maintains backward mechanical and electrical compatibility across revisions, so replacements usually drop in without issues.

Ordering Info: In-stock units ship within one week; delivery takes no more than a month even during supply chain delays. Payment terms are 50% upfront, balance before shipment. We ship via FedEx, UPS, or DHL depending on destination and urgency.