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 

X-21s | Four Relay Expansion Module

X-21s Relays: 4 Form 1C / SPDT
(125VAC, 28VDC, 2.5A)
9-28 VDC (supplied via the X-400 or X-600M controller, 24V recommended)


  • 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…

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
  • 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)


  • 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


  • 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


  • 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)

Product Safety Compliance

  • IEC 61010-1 (Electrical Equipment for Measurement, Control, and Laboratory Use)
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