X-21S™ | Relay Form C / SPDT Expansion Module

$179.99

The X-21S™ adds four Form-C (SPDT) relays, each rated at 2.5A, to an X-400™ or X-600M™ controller. Designed for light-duty switching, it provides reliable control in applications where smaller loads need to be managed efficiently.

Multiple X-21S™ modules can be connected via ribbon cable, which supplies both power and communication, enabling scalable relay expansion in larger systems.

4 Form-C/SPDT Relays

Expansion Module for the X-400 or X-600M

Frequently Bought Together
Expansion Cable
Expansion Cable


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Indicator Lights, Alarms, Pumps, & More

An X-400 or X-600M connected with an expansion module like the X-21S provides 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.

See All Expansion I/O

X-21S Features

  • 4 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)

X-21S Master Devices

  • X-400™ | Modular I/O Controller

    X-400™ | Modular I/O Controller

     Price range: $299.99 through $399.99
    TThe X-400™ is a scalable Ethernet-based controller that supports up to 32 local expansion modules or remote ControlByWeb® devices through peer-to-peer communication, enabling systems with up to 64 I/O points. Its browser-based interface and embedded GUI logic builder provide event-driven automation for powerful turn-key solutions and seamless integration with SCADA and PLC platforms—without licensing fees.

    X-400C™ – Cellular-Enabled Model
    The X-400C™ adds a built-in cellular modem, extending the same modular control and integration capabilities to remote or distributed applications.
    • Expandable, Up to 64 I/O
    • Relays, Analog & Digital Inputs
    • Up to 16 temp sensors
    • Cellular version available
    Global Cellular Coverage. Discuss international cellular options with a sales engineer.

    [frequentlyBought ids="7635,34491,7624,7577"]

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  • X-600M expandable I/O controller

    X-600M™ | Web-Enabled I/O Controller

     $549.99
    The X-600M™ is ControlByWeb’s most advanced controller, built for large-scale industrial and OEM applications. Supporting up to 64 expansion modules and 1,024 I/O points, it’s engineered for high-density, complex systems.

    With an embedded logic builder, LUA scripting for advanced control, and support for multiple customizable dashboards, the X-600M™ gives engineers powerful tools for automation and visualization. Open protocol support (Modbus, SNMP, peer-to-peer) ensures seamless integration with SCADA and PLC systems, delivered without licensing fees or proprietary lock-in.
    • Expandable, Up to 1,024 I/O
    • Relays, Analog/Digital/Thermocouple Inputs
    • Up to 32 Temperature Sensors
    • GUI Dashboard

    [frequentlyBought ids="7635,7621,7318,7289"]

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(Example images are shown. Label and terminal connector may differ)

Specifications

Power Requirements
  • Voltage: 9-28 VDC (supplied via the X-400 or X-600M controller, 24V recommended)
  • Max Current:
Power Supply All Relays OFF All Relays ON
9 VDC 17 mA 270 mA
12 VDC 13 mA 189 mA
24 VDC 7 mA 110 mA

Relay Contacts
  • Number of Relays: 4
  • Max Voltage: 125VAC, 28VDC
  • Max Current: 2.5A
  • Contact Type: SPDT (Form C)
  • Load Type: General Purpose
  • Contact Resistance: < 100 milliohms initial
  • Contact Material: AgNi
  • Electrical Life: 100K operations (Min)
  • Mechanical Life: 5M cycles (Min)
  • Environmental Rating: Over voltage Category II, Pollution Degree 2
  • Relay Modes: ON/OFF or Pulsed
  • Pulse Timer Duration: 0.1 to 86,400 Seconds (1-day)
Connectors
  • Relays: 12-Position, 3.81mm terminal spacing, Removable. For 16-28 AWG wire.
  • Expansion Connector: Ribbon cable, 10-conductor, polarized, 2×5-position, 0.100″ pitch Provides power and communications for expansion modules (Communications: RS-485)
LED Indicators
  • Number of LEDs: 5
    • Power on
    • Relay coil energized 1-4
Physical
  • Size:
    • 1.41in (35.7mm) wide
    • 3.88in (98.5mm) tall
    • 3.1in (78mm) deep (not including connector)
  • Weight: 4.8 oz (136 g)
  • Enclosure Material: Lexan 940 Polycarbonate Plastic
  • Enclosure Flame Rating: UL94 V0
Environmental
  • Operating Temperature: -40°F to 122°F (-40°C to 50°C)
  • Storage Temperature: -40°F to 185°F (-40°C to 85°C)
  • Humidity: 5-95%, non-condensing
  • Altitude: Up to 2,000m
  • Indoor use or NEMA-4 protected location
Electromagnetic Compliance
  • IEC CISPR 22, CISPR 24
  • FCC 47CFR15 (Class B)
  • EN55024 ITE Immunity (2010)
  • EN55022 Emissions (2010)

 

Manuals & Downloads

Users Manuals

X-21S™ Users Manual (PDF)

Catalog

X-21S™ Data Sheet (PDF)

ControlByWeb Product Catalog

Other Downloads

X-21S 3D Model (.stp)

Accessories

 

Cloud Seat Icon

ControlByWeb Cloud Device Seat

$11.99

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Expansion Cable

Expansion Cable

$10.00

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For your convenience we have set up a live X-600M unit connected to several expansion modules (i.e., X-11S™, X-12S™, X-13S™, X-15S™,and X-16S™). The X-21S™ will be connected and used similarly to these expansion modules. These expansion modules contain a variety of inputs and outputs that allow you to see how the X-600M works with its expansion modules. By clicking the links below you have full access to these live units. You can make changes to the configuration and settings through the setup pages and you can control the expansion modules’ relays, and view the current status of the inputs, and monitor temperature (X-600M & X-13S™) through its dashboard page.

X-332™

Digital Input Control Page

X-600M™

Control Page Setup Pages*

*Setup page login information:

Username: admin

Password: webrelay

X-600M live demonstration setup

Live Demo With One of Our Sales Engineers

Let’s make it easy with a live demo and screen sharing.

Set up a one-on-one Q & A with one of our experts. We’ll help you find the best solutions for your next project and walk you through a demonstration.

Schedule Free Consultation

 

Low on time? Watch a pre-recorded demo instead:

X-600M Setup and Programming Demo

X-600M Setup

The diagrams illustrate how this demonstration is wired. The relays on all expansion modules are not connected to a load; however, you can still access and control the relays by turning them on or off through the X-600M dashboard. The X-600M is also wired to a temperature sensor, and the X-13S is connected to a thermocouple. Both sensors can be monitored on the X-600M’s dashboard. The digital input states on the X-15S only changes when a voltage is applied to the inputs. For this demonstration, we have connected one of our X-332 controllers to Input 1 on the X-15S. You can apply a voltage to this input by accessing the control page for the X-332 (Digital Input Control Page).

Important Information

  • Multiple users may be accessing this device simultaneously so the device can change while you are using it.
  • This unit will be reset to factory defaults daily at 2:30AM MST.
  • Please DO NOT change network or password settings.

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    WebRelay-Quad™ | 4 Web-Controlled Relays

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    The WebRelay-Quad streamlines relay control with powerful yet accessible options, including a conditional and scheduled logic builder with intuitive drop-down menus, seamless open API integration via your own software, or communication using industrial protocols like MQTT and Modbus TCP/IP. Note: This is the new WebRelay-Quad. See the original WebRelay-Quad here.
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    • Ethernet, Cellular, or WiFi
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  • X11S High-Current Relay Expansion Module

    X-11S™ | High-Current Relay Expansion Module

     $179.99
    The X-11S™ adds two 20A Form-C (SPDT) relays to an X-400™ or X-600M™ controller, providing rugged, high-current switching for demanding industrial and OEM applications. Terminated through heavy-duty screw terminals, it is designed for reliable operation in environments where durability and load capacity are critical.

    Multiple X-11S™ modules can be connected to the host controller via ribbon cable, which supplies both power and communication, enabling scalable relay expansion without additional wiring complexity.

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    Expansion Module for the X-400 or X-600M

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  • X-401 with Cell, WiFi, and POE icons

    X-401™ | Dual Relay and Input Module

     Price range: $269.99 through $369.99
    The X-401™ combines two SPDT (Form C) relays with two optically isolated inputs in a compact, industrial-grade module. As part of the 400 Series, it features a browser-based interface, embedded GUI logic builder, and open protocols (Modbus, MQTT, SNMP, REST) for seamless integration with SCADA, PLC, and IIoT systems.
    Ideal for applications such as process monitoring, equipment reboot, and alarm control, the X-401™ provides a reliable edge-control solution that eliminates licensing fees and reduces integration complexity.
    • 2 Relays & 2 Digital Inputs
    • Ethernet, Cellular, or WiFi
    • 9-28VDC and/or POE
    Cellular and WiFi are Now Available. Note that X-401CW and X-401W models include cellular and WiFi capability respectively, which allows for more flexibility for your application.
    Global Cellular Coverage. Discuss international cellular options with a sales engineer.

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    View Product This product has options that may be chosen on the product page
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400 Series Guided Demo

Self-Guided, Live Demo of our Products

SETUP PAGES

Use the Setup Page to set up I/O, change settings, and create logic with intuitive dropdown menus.

CONTROL PAGE

Use the Control Page to see I/O status and manually control relays.

*Setup page login information: Username: admin Password: webrelay

Schedule A Guided Walkthrough

Want a little extra guidance? Schedule a 15-minute guided demo with our sales engineers. They’ll show you how it works for your application.

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