How-To Guide  ·  Allen-Bradley POINT I/O (1734)  ·  Power & Wiring

1734 POINT I/O: Power Architecture, Expansion Supplies, and Wiring Guide

Platform: POINT I/O (Bulletin 1734)  ·  Up to 63 modules per adapter  ·  EtherNet/IP, DeviceNet, ControlNet, PROFIBUS

1. How POINT I/O Power Works

A POINT I/O system has two completely separate power paths:

How It Flows

The communication adapter (e.g., 1734-AENT) is always the leftmost device in the rack. It accepts 24V DC on its power input terminals, converts a portion to 5V DC for the POINTBus backplane, and passes the remaining 24V DC through to the field power bus bars in the terminal bases. Every module to the right of the adapter receives both power domains through the interlocking terminal base connections.

As you add modules to the right, two things happen:

1. POINTBus current increases — each module draws 50–220 mA from the 5V backplane. When the adapter’s POINTBus capacity is exhausted, you must add an expansion power supply.
2. Field power current increases — output modules and sensor-powered inputs draw from the 24V DC field bus. The maximum field current through the terminal base bus bars is 10A.

2. Power Components Overview

There are four types of power-related components in the POINT I/O platform:

3. Communication Adapter Power

The communication adapter is the starting point for all power in a POINT I/O system. It has a built-in power supply that converts the incoming 24V DC to 5V DC for the POINTBus backplane while passing 24V DC through for field power distribution.

Adapter Power Specifications

Adapter Wiring

The communication adapter has three power terminals:

How Many Modules Can an Adapter Support?

The adapter powers modules to its right on the backplane. The number of modules depends on which modules you use and their individual POINTBus current draws:

• 1734-AENT (1.0A): Up to 13 modules at 75 mA each (13 × 75 = 975 mA, under the 1,000 mA limit)
• 1734-AENTR (0.8A): Up to 10 modules at 75 mA each (10 × 75 = 750 mA, under the 800 mA limit)

If you use modules with higher current draws (e.g., 1734-IR2 at 220 mA), the count drops significantly. See the POINTBus current budget section below for exact calculations.

4. POINTBus Current Budget

Every I/O module on the POINT I/O backplane draws a specific amount of current from the 5V POINTBus. You must add up the current draw of all modules in a power segment and ensure it does not exceed the capacity of the adapter or expansion power supply feeding that segment.

POINTBus Current Draw per Module

How to Calculate Your Budget

1. List every I/O module in the system from left to right (starting after the adapter).
2. Look up each module’s POINTBus current from the table above.
3. Add up the current for all modules to the right of each power source (adapter or expansion supply).
4. Compare to the capacity of the adapter or expansion supply feeding that segment.
5. If the total exceeds the capacity, insert a 1734-EP24DC expansion power supply. Modules after the EP24DC draw from its capacity, not the adapter’s.

Example Calculation

System with a 1734-AENT adapter (1.0A POINTBus capacity):

At slot 8, the total exceeds the adapter’s 1,000 mA capacity. You need a 1734-EP24DC inserted before slot 8. The EP24DC resets the running total for all modules to its right.

5. When to Add Expansion Power (1734-EP24DC)

The 1734-EP24DC is a 24V DC expansion power supply that adds POINTBus capacity and starts a new field power segment for modules to its right. It mounts on a terminal base just like an I/O module.

Signs You Need an EP24DC

• Your POINTBus current budget calculation exceeds the adapter’s capacity (see Section 4)
• You are adding more than 13 modules to a single adapter
• You want to start a separate 24V DC field power segment with its own power supply
• You are using a 1734-ADN (DeviceNet) adapter with 36+ modules — use at least 2 expansion power supplies

1734-EP24DC Specifications

Where to Place the EP24DC

Insert the EP24DC into the rack at the point where the cumulative POINTBus current of the modules to its left is approaching the adapter’s limit. The EP24DC powers all modules to its right, resetting the POINTBus budget. The adapter continues to power all modules between itself and the EP24DC.

EP24DC Wiring

The 1734-EP24DC requires its own 24V DC power input, separate from the adapter:

6. AC Field Power (1734-EPAC)

The 1734-EPAC is an AC expansion power supply for systems that include AC I/O modules (e.g., 1734-IA2, 1734-IA4, 1734-OA2, 1734-OA4). It accepts 120/240V AC input, generates 5V DC for the POINTBus, and distributes AC field power to modules on its right.

1734-EPAC Specifications

When to Use the EPAC vs. EP24DC

7. Field Power Distributor (1734-FPD)

The 1734-FPD is a field power distributor that breaks the field power bus and starts a new field power segment. Unlike the EP24DC and EPAC, the FPD does not generate any POINTBus power — it simply passes the 5V backplane through while creating a clean break in the field power distribution.

1734-FPD Specifications

Use Case 1: Separate AC and DC Field Power

When your rack has both DC digital modules and AC digital modules, use the FPD to create a boundary between them:

Use Case 2: Isolate Analog from Digital Power

Analog modules can be sensitive to electrical noise from digital output switching. Use the FPD to give analog modules their own clean power supply:

Use Case 3: New Voltage Distribution Point

If the field power voltage needs to change at some point in the rack (e.g., from 24V DC to 12V DC), use the FPD to inject the new voltage:

8. System Design Examples

Example 1: Small System — 8 Digital I/O Modules (No Expansion Needed)

Application: A packaging machine with 32 digital inputs and 32 digital outputs.

Result: 600 mA total, well within the AENT’s 1,000 mA capacity. No expansion power supply needed. Single 24V DC power supply feeds the adapter. All 8 modules share the same field power bus.

Example 2: Medium System — 16 Modules with EP24DC

Application: A process skid with digital I/O, analog current loops, and RTD temperature inputs.

Result: Adapter segment uses 825 mA of 1,000 mA. EP24DC segment uses 790 mA of 1,300 mA. Both within limits. Two 24V DC power supplies: one for the adapter, one for the EP24DC.

Example 3: Mixed AC/DC System with FPD

Application: A building management panel with DC digital I/O and 120V AC contactors for HVAC.

Result: The FPD separates the 24V DC segment (slots 0–3) from the 120V AC segment (slots 4–5). The POINTBus backplane passes through the FPD unbroken — all modules still draw from the adapter’s 1,000 mA budget (450 mA total). The FPD requires its own 120V AC power input wiring.

9. Wiring Best Practices

24V DC Power Supply Requirements

Wire Gauge Recommendations

Torque Specifications

Grounding

• DIN rail grounding: Connect the DIN rail to the panel ground bus with a short, low-impedance ground conductor (14 AWG or larger).
• Functional earth (FE): Always connect the FE terminal on the adapter and expansion power supplies to the DIN rail or panel ground bus.
• Shield grounding: For shielded cables, land the shield on the nearest ground terminal. Do not daisy-chain shields.
• Analog shielding: Use individually shielded twisted-pair cable for all analog signals. Ground the shield at one end only (typically the controller end) to avoid ground loops.

Fuse Recommendations

• Adapter power input: 10A or 15A fuse/breaker on the 24V DC supply feeding the adapter
• EP24DC power input: Separate 10A fuse on the 24V DC supply feeding each expansion power supply
• EPAC power input: 10A fuse/breaker on the AC supply feeding the EPAC
• Output modules: Fuse individual output circuits per the I/O module documentation (typically 2A per point for 1734-OB8)

DIN Rail Mounting

• Use EN50022 standard DIN rail (35 × 7.5 mm)
• Mount the rail horizontally for best thermal performance (the EP24DC has reduced POINTBus capacity in vertical mounting)
• Leave 50 mm (2 in.) minimum clearance above and below the modules for airflow
• Ensure all terminal bases are fully seated and interlocked — the POINTBus passes through the base-to-base mechanical connection

10. Related Guides & Resources

Reference Documentation

The following Rockwell Automation publications were used as references for this guide. These are the official manufacturer documents for the hardware covered in this article.