1790-T0W8X Relay Module 8 Output Allen-Bradley

Allen-Bradley 1790-T0W8X 8 Relay Output Expansion Module

Product Introduction

The Allen-Bradley 1790-T0W8X gives you eight independent relay outputs in a compact expansion module. Each relay uses Form A (normally open) single-pole single-throw contacts. Unlike solid-state outputs, these mechanical relays handle mixed AC and DC loads with ease. You can switch 2.0A resistive at 125V AC, 250V AC, or 5-28V DC. For 48V AC applications, the rating is 0.8A resistive. The minimum load requirement is very low at just 100µA with 100mV DC. Therefore, the 1790-T0W8X works perfectly for both small signal switching and power load control. Each output channel has its own dedicated COM terminal, which gives you maximum wiring flexibility.

Technical Specifications of the 1790-T0W8X

Relay Output Characteristics

• Number of outputs: 8 relay outputs.

• Relay type: Form A, normally open, single pole single throw (SPST).

• Output voltage range (load dependent):

  • 5…28V DC at 2.0A resistive

  • 48V AC at 0.8A resistive

  • 125V AC at 2.0A resistive

  • 250V AC at 2.0A resistive

• Minimum load: 100 µA at 100mV DC.

• On-state voltage drop: 0.5V maximum at 2.0A, 24V DC resistive load.

• Initial contact resistance: 30 mΩ.

• Expected contact life: 300K cycles resistive, 100K cycles inductive.

• Off-state leakage current: 1.5 mA maximum.

• Output delay time (Off to On): 10 ms maximum.

• Output delay time (On to Off): 10 ms maximum.

• Indicators: 8 green status LEDs, one per relay.

• Common type: 1 point shares 1 COM (each output has its own COM terminal).

Field Power Specifications

• Supply voltage: 24V DC nominal.

• Voltage range: 19.2…28.8V DC.

• Power dissipation: 2.3W maximum at 28.8V DC per channel (coil power).

Isolation and Wiring

• Isolation (I/O to logic): Photocoupler isolation.

• Isolation voltage: 1250V AC RMS.

• Terminal block: M3.0 screws.

• Screw torque: 7 lb-in maximum.

• Conductor material: Copper or copper-clad aluminum only.

Mechanical and Environmental Data

This module weighs only 0.17 kg (0.38 lbs). Its lightweight design makes it ideal for high-density installations. Operating temperature ranges from 0°C to 55°C. Storage temperature extends from -40°C to 85°C. Relative humidity can reach 5% to 95% non-condensing. Additionally, the 1790-T0W8X meets standard industrial shock and vibration requirements. You can mount it on a standard DIN rail or directly on a panel. Keep the module away from high-voltage cables and heat sources to maximize relay contact life.

Frequently Asked Questions (FAQ)

1. Can I switch both AC and DC loads on the same 1790-T0W8X module?
Yes, absolutely. Each relay contact is voltage-independent. For instance, you can switch 250V AC on channel 0 and 24V DC on channel 1. Just respect the maximum current rating for each voltage.

2. Why does the 48V AC rating show only 0.8A while 125V AC shows 2.0A?
This difference comes from arc suppression characteristics. At 48V AC, the arc extinguishes less reliably than at higher voltages. Therefore, Allen-Bradley derates the 48V AC current to 0.8A to ensure contact life.

3. How do I protect the 1790-T0W8X relays from inductive load damage?
Install a snubber circuit (resistor-capacitor network) or a flyback diode across the load. For AC loads, use a metal oxide varistor (MOV) or RC snubber. For DC loads, use a flyback diode across the relay coil or load. These devices absorb arc energy.

4. What happens if I exceed 100,000 cycles on an inductive load?
The contacts may become pitted or welded closed. On-state resistance increases gradually. Finally, the contact may fail to open or close. For critical applications, replace the 1790-T0W8X before reaching the rated cycle life.

5. Does the 1790-T0W8X require external 24V DC field power to operate?
Yes, the module needs 24V DC nominal (19.2-28.8V DC) for the relay coils. This power is separate from the load voltage. Without field power, the relays remain de-energized even if the logic side sends an On command. The green LEDs also require this field power to illuminate.