Allen-Bradley 1771-OX Power Contact Output Module

The Allen-Bradley 1771-OX Power Contact Output Module is a four-channel PLC-5 I/O card that uses mercury-wetted relays to switch external power to connected loads. Designed for use in a PLC-5 system, this module plugs into a 1771 I/O chassis backplane and provides four independently powered contact outputs, enabling the PLC to control external devices such as motors, solenoids, or heaters with an isolated, mechanical switch. The mercury-wetted relay design offers robust switching performance in industrial environments where electrical noise and transient conditions are common, delivering clear separation between the controller’s logic and the external power path. As a dedicated power-contact output module, the 1771-OX is intended to drive externally powered loads while the PLC-5 manages the switching via its program and I/O addressing, making it suitable for expanding digital output capability in legacy automation setups. In practice, the module supports load switching through four contacts within a PLC-5 rack, providing a compact solution for adding reliable, high-side or low-side switching to legacy control schemes where solid-state or mechanical relays are preferred for durability and simplicity.