1794-OM8 PLC I/O Digital Module

1794-OM8 I/O Digital Module

The 1794-OM8 Flex I/O Digital Output Module has 8 Nonisolated Outputs, a 240V AC Output Voltage nom., and a 4.0A Output Current Rating. It also operates with a 1.5V AC @ 0.5A On-state Voltage Drop max. and a 2.5mA Off-state Leakage max.

1794-OM8 Specifications

Outputs:8 Nonisolated
Output Voltage nom.:240V AC
Output Current Rating:4.0A
On-state Current max.:500mA per Output
On-state Voltage Drop max.:1.5V AC @ 0.5A
Off-state Leakage max.:2.5mA
Isolation Voltage:250V Continuous
Flexbus Current:60mA @ 5V DC
Power Dissipation:5W @ 0.5A max.
Thermal Dissipation:17.1 BTU/hr. @ 0.5A max.

1794-OM8 FAQ

Q: What does "Nonisolated outputs" mean for this module?
A: Nonisolated outputs mean that the 8 output channels share a common electrical reference. All channels are referenced to the same common terminal on the terminal base. This simplifies wiring for non-critical applications but provides less channel-to-channel fault protection compared to individually isolated or group-isolated modules. This configuration is suitable for applications where field devices operate from a single AC supply.

Q: What is the maximum current the module can switch simultaneously across all 8 channels?
A: The 1794-OM8 has a total output current rating of 4.0A across all 8 channels. With each channel capable of 500 mA maximum, you must ensure that the sum of currents on all active channels does not exceed 4.0A. For example, you cannot switch all 8 channels at 500 mA simultaneously (8 × 0.5A = 4.0A would be at the exact limit). Careful load distribution is required.

Q: What does the off-state leakage current specification mean, and how could it affect my application?
A: The maximum off-state leakage current of 2.5 mA means that even when an output is OFF, a small current may still flow through the solid-state switching device (triac/SCR). In certain sensitive applications, this leakage could cause a high-impedance load (like a small relay coil or indicator lamp) to remain faintly energized or prevent full turn-off.