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What is accessory 18RX (Relay Expansion Module) and how does it work with a Group G Controller?

​​​​Accessory 18RX also known as REX (Relay Expansion Module) is an optional accessory for the Group G controller. Up to two 18RX modules can be added to an Open Transition Transfer Switch (3ATS) while only one can be added to a Delayed Transition Transfer Switch (3ADTS) since one REX module is already present on this type switch.

Primary functions and features of 18RX (Relay Expansion Module) are as follows:
  • To interface the controller with a dual operator switching device thus one (1) REX module is already built into the 3ADTS
  • REX Module Provides the Following Relays:
    • OP2 And OP3 Relays and Terminal Block Connections
      • The Default Function of OP2 Relay Is to Provide A Common Alarm Output to Indicate A Common Alarm
    • Can Be Configured For:
      • Common Alarmsimage.png
      • Accessory 31 - Selective Load Disconnect Feature
      • Acc. 1G - Auxiliary power connections provide for connection of external 24VDC source to power control panel when normal and emergency sources are not present. Allows for use of full range of extended engine starting time delay feature 1C (0-60min 59 sec)
      • Not In Auto - the output contacts change position when the transfer is being inhibited from transferring to the emergency source (Feature 34B) or the transfer switch has been set for Non-Automatic (Manual) operation.
      • NR2 - an additional engine start contacts.
    • 18B,18G Relay, and Terminal Block Connections
      • 18B Relay Is Energized When Emergency Source Is Accepted.
      • 18G Relay Is Energized When Normal Source Is Accepted.
    • REX Module Can Be Daisy Chained to Allow Multiple Sets Of Contacts Via 2nd REX Module


Refer to User’s Guide, ASCO Group G Controller for Automatic & Non-Automatic Transfer Switches, Part Number 381333-400 for additional setting information. Download Link

If unsure, contact Technical Support at 1-800-800-ASCO or send an email to technicalsupport@ascopower.com

ASCO Power Technologies USA

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