Allen-Bradley 1734-OB8 POINT I/O 8-Point 24V DC Sourcing Output Module

Eight sourcing outputs for relays, solenoids and indicators

The Allen-Bradley 1734-OB8 is a POINT I/O digital output module with eight 24V DC sourcing outputs in a single group. Each output can switch up to 1.0 A, which is enough for interposing relays, small solenoid valves, pilot lights and beacons, with a limit of 3.0 A for the whole module.

It belongs to the same family as the 1734-OB2 and 1734-OB4, which have fewer points, and to the protected 1734-OB8E, which adds electronic output protection. The OB8 itself does not list a fault indication per output.

Technical specifications

Switching behaviour and limits

The sheet gives an on-state voltage range of 10 to 28.8V DC, with a drop of up to 0.2V DC and a leakage of 0.5 mA at 28.8V DC in the off state. Switching delay is 0.1 ms in both directions, and surge current can reach 2 A for 10 ms once every 3 seconds, which helps with lamp and relay inrush.

Because outputs are sourcing, the load connects between the output terminal and the field common. Add a freewheel diode across inductive loads and check that the sum of the output currents stays within the module limit. Power dissipation reaches 2.0 W at 28.8V DC.

Installation and system notes

The module needs 24V DC (10 to 28.8V DC) field power at 32 mA, plus 75 mA from POINTBus. It sits on a 1734-TB, 1734-TBS, 1734-TOP or 1734-TOPS base. The isolation voltage is 50V continuous with reinforced insulation, type tested at 2500V DC for 60 seconds between field side and system.

Eight yellow LEDs show each output state and two green/red LEDs show module and network status. The default data map uses one byte for the outputs. As with all POINT I/O modules, remove or fit the module only as the installation sheet allows, and mount the node in a suitable enclosure.

Documents and quotation

The sheet 1734-IN018 covers the output modules of this family. When you request a quotation, give the 1734-OB8 reference, series, quantity, the adapter or controller and the loads. The protected 1734-OB8E is a different catalog number. See PLC & I/O Cards.

How the 1734-OB8 Works

Each output of the 1734-OB8 is a solid-state switch on the high (positive) side of the load. When the controller turns an output on, the module connects the 24V DC field power from the terminal base to the output terminal, and current flows through the load to the field common. This is called a sourcing output, and it suits loads wired to 0V, which is the usual practice in European and Middle Eastern panels. Because there are no moving contacts, the outputs switch in about 0.1 ms and do not wear, so the module suits loads that switch frequently.

The module takes its logic power from POINTBus and its output power from the field power bus that runs through the terminal bases. If the field power is lost, the outputs cannot energise their loads even though the module still communicates, which is a useful point to remember when fault finding.

Selection & Ordering Guide for the 1734-OB8

• 1734-OB8 – eight 24V DC sourcing outputs, 1.0 A each, 3.0 A per module.
• 1734-OB8K – conformal-coated version for harsh atmospheres.
• 1734-OB8E – protected version with electronic output protection and diagnostics.
• 1734-OB4 and 1734-OB2 – lower point counts for smaller nodes.
• 1734-OW2 – relay outputs where loads need isolation or a different voltage.

For eight loads on one module you will usually need a terminal base with enough common terminals, such as a 1734-TOP or a three-wire base, or a separate common distribution. Our team can help confirm the correct ordering code when you request a quote.

Installation & Maintenance of the 1734-OB8

• Fit a freewheel diode across solenoid and relay coils to protect the output and reduce interference.
• Keep the total load current within 3.0 A for the module, and check that the field power supply and the adapter or potential distributor can carry the current of all modules in the power group.
• Protect the 24V DC field supply with a suitable fuse or circuit breaker; where electronic output protection and diagnostics are required, choose the 1734-OB8E instead.
• POINT I/O supports removal and insertion under power, but only when the area is known to be non-hazardous.
• When fault finding, compare the yellow output indicator with the load: if the indicator is on but the load does not energise, check field power and wiring before replacing the module.

Typical Applications in Oman & the GCC

The 1734-OB8 drives interposing relays for motor starters, small solenoid valves on water treatment and dosing skids, beacons and sounders on alarm panels, and indicator lamps on local control stations. It is used in remote I/O panels on pumping stations, packaging and conveyor lines, and oil and gas skids, where eight outputs in a 12 mm slot keep the enclosure compact.

Why Source from Seven Star LLC

Seven Star LLC is an independent supplier in Muscat. Seven Star LLC supplies Allen-Bradley POINT I/O and other automation components across Oman and the GCC. Send the 1734-OB8 catalog number, the quantity and your load list and request a quote; our team can help confirm the correct ordering code, terminal base and adapter.