ARA-120-AHE Special Function Triplexer Alternating Relay

The ARA-120-AHE special function triplexer alternating relay from the ATC Diversified Electronics Division of Marsh Bellofram are designed for use in three-load installations.  This model has a field selection switch that is used to omit one of the three loads for general or emergency maintenance while depleting the remaining two loads.

The ARA-120-AHE Special Function Triplexer Alternating Relay has the option of alternating on each load cycle or by external clocking. This alternating relay also allows for additional loads to run in the event of excess load requirements. The alternating action is initiated by the control switch between terminals 2 and 4 when the factory installed jumper is in place between terminals 3 and 4. The alternating action may be initiated externally by removing the factory installed jumper between terminals 3 and 4 and placing an isolated normally open switch between terminals 2 and 3. An alternating action will occur each time this isolated switch is closed and then re-opened.

The selection switch has the following positions:
Normal — Normal operation as Triplexer
Omit 1 — Omit load #1 Duplex loads 2 and 3
Omit 2 — Omit load #2 Duplex loads 1 and 3
Omit 3 — Omit load #3 Duplex loads 1 and 2

In the event of a power failure, the alternating relay will return to its quiescent state and continue sequencing loads on one-at-a-time. Note: When the “omit load” option is selected, full potential will appear on the output terminal of the omitted load when the lag switch between terminals 2 and 5 closes. It is recommended that the H-O-A switch be placed in the “off” position for the omitted load.



  • Designed for three-load applications
  • Special function switch omits one load for emergency maintenance requirements
  • LED’s indicate output conditions
  • Surface mounted enclosure


  • Municipal water plants
  • Wastewater treatment facilities
  • Large aquarium pumps
  • Water well installations
  • Level and pumping control systems
  • Industrial pump level monitoring applications