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5 Designing the Power Supply System
5 - 12 NX-series EtherCAT Coupler Unit User’s Manual (W519)
 Maximum I/O Power Supply Current
The maximum I/O power supply current is the maximum current that the I/O power supply that is
connected to the EtherCAT Coupler Unit or Additional I/O Power Supply Unit can supply through the
NX bus connectors to the NX Units. For the maximum I/O power supply current of the EtherCAT
Coupler Unit, refer to
3-1-2 EtherCAT Coupler Unit Specifications on page 3-2. For the maximum I/O
power supply current of the Additional I/O Power Supply Unit, refer to the NX-series System Units
User’s Manual (Cat. No. W523).
The total current consumption from the I/O power supply from the NX bus is the total of the following
current consumptions.
• The current consumption from the I/O power supply that is required for the EtherCAT Coupler Unit or
the Additional I/O Power Supply Unit, and for the NX Units that are connected to the EtherCAT Cou-
pler Unit or Additional I/O Power Supply Unit
• The current consumption between the NX Units and the connected external devices
 Calculation Examples
Examples of calculating the current consumption from the I/O power supply are given below for a
Digital Input Unit and Digital Output Unit.
Calculating the Total Current Consumption from the I/O Power Sup-
ply
Current consumption item Description
Current consumption from I/O
power supply This is the current that is consumed by the internal circuits that operate on
the I/O power supply.
Specific values are given in the user’s manuals for individual Units.
Current consumption between
the NX Units and the connected
external devices This is the current that is consumed between the NX Units and the con-
nected external devices.
For example, this is the current consumed by a Digital Input Unit to supply
power to photoelectric sensors or to turn ON the input circuits in the Digital
Input Unit.
The current consumption depends on the type of I/O circuit in the NX Unit,
the number of I/O points that are used, and the current consumption of the
connected external device. It must be calculated for each NX Unit.
Current consumption of Digital
Input Unit
=
Current consumption from I/O power (Input current × Number
of inputs used) + Total current consumption of connected input devices
Current consumption of Digital
Output Unit
=
Current consumption from I/O power Total load current of con-
nected loads + Total current consumption of connected output devices