4-4
Selecting External Power Supplies
and Protective Devices
This section describes how to select the Unit power supply and the I/O power supply which are the
external power supplies for the CPU Rack, and how to select the protective devices.
4-4-1
Selecting the Unit Power Supply
This section describes how to select the Unit power supply for the CPU Rack.
Recommended Power Supplies
Use an SELV power supply that meets the following conditions for the Unit power supply.
• Has overcurrent protection.
• Has double or reinforced insulation between the input and output.
• Has an output voltage of 24 VDC (20.4 to 28.8 VDC).
Recommended Power Supplies: S8VK-S Series (manufactured by OMRON)
Calculating the Required Power Supply Capacity of the Unit Power
Supply
l
Formula
This section describes how to calculate the required capacity of the Unit power supply for the CPU
Rack.
Required capacity of the Unit power supply for
the CPU Rack
= Total of required Unit power supply capacity for
each block
Use the following formula to calculate the required Unit power supply capacity for each block in the
CPU Rack.
Required Unit power supply capacity of the CPU Unit
block = (A) + (B)/(C)
Required Unit power supply capacity of an Additional NX Unit Power Supply Unit block = ((D) +
(E))/(F)
(A) Unit power consumption of the CPU Unit
(B) Total NX Unit power consumption of NX Units that are connected to the CPU Unit
(C) NX Unit power supply efficiency of the CPU Unit
(D) NX Unit power consumption of the Additional NX Unit Power Supply Unit
(E) Total NX Unit power consumption of NX Units that are connected to the Additional NX Unit
Power Supply Unit
(F) NX Unit power supply efficiency of the Additional NX Unit Power Supply Unit
4 Designing the Power Supply System
4-22
NX-series NX1P2 CPU Unit Hardware User’s Manual (W578)
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