Power Budget
All FX2N CPUs have an internal power supply that provides power for the CPU, the expansion modules, and other 24 VDC user power requirements.
The FX2N CPU provides the 5 VDC logic power needed for any expansion in your system. Pay careful attention to your system configuration to ensure that your CPU can supply the 5V power required by your selected expansion modules. If your configuration requires more power than the CPU can supply, you must remove a module or select a CPU with more power capability.
All FX2N CPUs also provide a 24 VDC sensor supply that can supply 24 VDC for input points, for relay coil power on the expansion modules, or for other requirements. If your power requirements exceed the budget of the sensor supply, then you must add an external 24 VDC power supply to your system. Refer to Appendix A for the 24 VDC sensor supply power budget for your particular FX2N CPU.
If you require an external 24 VDC power supply, ensure that the power supply is not connected in parallel with the sensor supply of the FX2N CPU. For improved electrical noise protection, it is recommended that the commons of the different power  supplies be connected.
Guidelines for Grounding and Wiring
Proper grounding and wiring of all electrical equipment is important to help ensure the optimum operation of your system and to provide additional electrical noise protection for your application and the FX2N.
Prerequisites
Before you ground or install wiring to any electrical device, ensure that the power to that equipment has been turned off. Also, ensure that the power to any related equipment has been turned off.
Guidelines for Isolation
FX2N AC power supply boundaries and I/O boundaries to AC circuits are rated 1500 VAC.
These isolation boundaries have been examined and approved as providing safe separation between AC line and low voltage circuits.
All low voltage circuits connected to an FX2N, such as 24V power, must be supplied from an approved source that provides safe isolation from AC line and other high voltages. Such sources include double insulation as defined in international electrical safety standards and have outputs that are rated as SELV, PELV, Class 2, or Limited Power according to various standards.
Guidelines for Grounding the FX2N
The best way to ground your application is to ensure that all the common and ground connections of your FX2N and related equipment are grounded to a single point. This single point should be connected directly to the earth ground for your system.
For improved electrical noise protection, it is recommended that all DC common returns be connected to the same single-point earth ground. Connect the 24 VDC sensor supply common to earth ground.
All ground wires should be as short as possible and should use a large wire size, such as 2 mm2 (14 AWG).

When locating grounds, remember to consider safety grounding requirements and the proper operation of protective interrupting devices.
Guidelines for Wiring the FX2N
When designing the wiring for your FX2N, provide a single disconnect switch that simultaneously removes power from the FX2N CPU power supply, from all input circuits, and from all output circuits. Provide over current protection, such as a fuse or circuit breaker, to limit fault currents on supply wiring. You might want to provide additional protection by placing a fuse or other current limit in each output circuit.
Install appropriate surge suppression devices for any wiring that could be subject to lightning surges.
Avoid placing low-voltage signal wires and communications cables in the same wire tray with AC wires and high-energy, rapidly switched DC wires. Always route wires in pairs, with the neutral or common wire paired with the hot or signal-carrying wire.
Use the shortest wire possible and ensure that the wire is sized properly to carry the required current. The connector accepts wire sizes from 2 mm2 to 0.3 mm2 (14 AWG to 22 AWG). Use shielded wires for optimum protection against electrical noise. Typically, grounding the shield at the FX2N gives the best results. PLC可编程控制器英文参考文献和中文翻译(5):http://www.youerw.com/fanyi/lunwen_3792.html