Power Considerations - Allen-Bradley 1769-PA2 Installation Instructions Manual

• Total 24V DC sensor power (1769-PA2 only)
3. If your power supply load is at or above the limits of the allowable ranges that are shown
in the graphs, you must add an additional I/O bank.
See Connect the Power Supplies on page 19
IMPORTANT An additional I/O bank must include its own power supply.
An end cap/terminator (1769-ECR or 1769-ECL) must also be used if the I/O bank is the last in
the system.

Power Considerations

The following sections explain power considerations for the Compact I/O system.
Disconnect the Main Power
WARNING: EXPLOSION HAZARD
Do not replace components or disconnect equipment unless power has been switched off.
If you connect or disconnect wiring while the field-side power is on, an electrical arc can occur.
This could cause an explosion in hazardous location installations. Be sure that power is removed or
the area is nonhazardous before proceeding.
Install the main power disconnect switch where operators and maintenance personnel have
quick and easy access to it. Besides disconnecting electrical power, de-energize all other sources of
power (pneumatic and hydraulic) before you begin working on a machine or process that is
controlled by a controller.
Isolation Transformer Usage
You can use an isolation transformer in the AC line. This type of transformer provides isolation
from your power distribution system to reduce electrical noise and is often used as a step down
transformer to reduce line voltage. Any transformer that is used with the Compact I/O system
must have a sufficient power rating for its load. The power rating is expressed in volt-amperes
(VA). See Schematic (Using IEC Symbols) on page 18
transformers.
Power Supply Inrush
During powerup, the power supply allows a brief inrush current to charge internal capacitors.
Many power lines and control transformers can supply inrush current for a brief time. If the
power source cannot supply this inrush current, the source voltage can sag momentarily.
Rockwell Automation Publication 1769-IN028C-EN-P - August 2016
Compact I/O Expansion Power Supplies
for additional information.
for an example of circuits using isolation
15