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X-21s Four Relay Form C / SPDT Expansion Module
5 Year Warranty

X-21s expansion module with four relays can be controlled over the internet with an X-400 or X-600M controller.


The X-21s™ Four Relay Expansion Module is used with an X-400 or X-600M controller. The X-21s has four relays each with Form-C/SPDT contacts.

Required Controller

One or more X-21s expansion modules can be connected to an X-400/X-600M controller with an expansion cable. The expansion cable provides both power and communications to the expansion modules.

Controller Features

The X-400/X-600M are multi-function web-enabled industrial I/O controllers. They perform control, logic, and monitoring functions similar to that of a Programmable Logic Controller (PLC). However, unlike a PLC, these controllers are designed for web-based applications from the ground up.

No add-on software or hardware is required. The controllers can be fully configured, programmed and tested directly in the device using its built-in web server and a standard web browser. The web setup pages are intuitive and easy to use and do not require special programming skills.


The X-400/X-600M controllers, together with expansion modules, such as the X-21s, provide an easy, flexible, and reliable way to monitor and control systems and devices over a network. The X-21s is suitable for use with moderate loads such as solenoid valves, alarms, and indicator lights.

Other expansion modules with different I/O combinations are also available.

Tank Battery Level Monitoring with Pump and Valve Control


  • Four, Form C/SPDT relays (independently controlled)
    • Voltage: 125VAC, 28VDC
    • Current: 2.5A
  • LED indicators for relay and power status
  • Operating Temp: -40°F to 122°F (-40°C to 50°C)
  • Storage Temp: -40°F to 185°F (-40°C to 85°C)
  • Removable terminal connector
  • Powered through expansion bus - no separate power supply connections are required
  • Requires an X-400 or X-600M controller
  • Great for moderate-load applications including:
    • Solenoid valves
    • Alarms
    • Indicator lights
    • and much more...
CE listed RoHS compliant Made in the USA

X-21s | Four Relay Expansion Module

In Stock




Relays: 4 Form C / SPDT (Form C)
(125VAC, 28VDC, 2.5A)


9-28 VDC (supplied via the X-400 or X-600M controller, 24V recommended)



Please contact our sales department for quantity discounts.


More Information:


Where to Buy

Click "Buy Online" to view part numbers and pricing. X-21s is available in the USA and internationally, and can be purchased either from us or an Authorized Distributor.

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Warning: May contain chemicals, including Nickel (metallic), known to the State of California to cause cancer and reproductive harm. -



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