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4 Designing the Power Supply System
NX-series NX1P2 CPU Unit Hardware User’s Manual (W578)
4-4 Selecting External Power Supplies and Protective Devices
4
4-4-3 Selecting Protective Devices
This section describes how to select protective devices (e.g., breakers and fuses) to protect against
short circuits and overcurrents in external circuits.
Overcurrent is the current that flows when an excessive load is connected and one of the following rat-
ings is exceeded.
The built-in I/O overcurrent refers to a current that flows when the maximum switching capacity of the
built-in output is exceeded.
Use the I/O power supply current for the CPU Rack of NX1P2 CPU Unit at 4 A or less. Using
the currents that are outside of the specifications may cause failure or damage.
Consider the following items when you select protective devices.
• Protective device specifications (breaking/fusing, detection characteristics, steady current value, etc.)
• Inrush current when power is turned ON
• Inrush current when connected external devices turn ON and OFF
*1
*1. Refer to 4-3-5 Restrictions on Inrush Current for ON/OFF Operation on page 4-17 for information on the
inrush current when connected external devices are turned ON and OFF.
For the breaking/fusing time, use protective devices that meet the conditions in the following table.
For Unit Power Supply
4-4-3 Selecting Protective Devices
Unit Item for rating Rated value
CPU Unit NX Unit power supply capacity 10 W max.
Current capacity of power supply
terminal
4 A max.
Additional NX Unit Power Supply
Unit
NX Unit power supply capacity Refer to the NX-series System Units
User’s Manual (Cat. No. W523).
Current capacity of power supply
terminal
Additional I/O Power Supply Unit Maximum I/O power supply cur-
rent
4 A max.
*1
*1. Even if the model of the Additional I/O Power Supply Unit you use allows the maximum I/O power supply
current or current capacity of the I/O power supply terminals which is higher than 4 A, the I/O power must be
supplied at 4 A or lower because of the restriction on the CPU Rack system configuration.
Current capacity of I/O power
supply terminals
Selecting Protective Devices
Current Breaking/fusing time
6 A 1 min max.
12 A 15 s max.
21 A 5 s max.
30 A 2.5 s max.
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