When the line power supply exceeds 10 times the kv-a rating of the drive, add line reactors.

3% impedance line reactor shall be used to reduce the power line transient voltage caused by capacitor switch, line notch, DC bus overvoltage trip and inverter over-current and overvoltage conditions. Line reactors improve the true input power factor and reduce crosstalk between drivers. The input line reactor provides some protection for the driver under short circuit conditions. If the kv-a rating of the power transformer is greater than 10 times the kv-a rating of the driver, a line reactor is recommended to minimize damage to the driver in the event of a short circuit in the power transformer. This line impedance depends on the short circuit rating of the driver and the supply distribution transformer. Specifically, the line impedance must be greater than or equal to the ratio of the power transformer rating to the driver

Please use separate conduit for input power, output power and control wiring. More specifically, when connecting the power supply and control circuit of VFD, the following criteria should be followed:

Install the input AC power line in its own rigid steel pipe.

Install the output motor wiring in its own rigid steel pipe.

Install the control line in its own rigid steel pipe. Low voltage DC control lines and 120 VAC control lines shall be located in different conduits. When connected to the control board of VFD, twisted pair and shielded wire are enough. Two and three wire connections are recommended. For many drives, the minimum wire size is 18 AWG.

Ensure that all ground connections are secure and properly grounded. The shield should be grounded only at one end of the cable to avoid grounding loops. When connecting the shield at the VFD end, connect it to the chassis ground lug. Note: before connecting the shield to the ground strap of VFD, be sure to disconnect the power supply of VFD.

Separate control and feedback wiring from power cord for at least 12 inches. Note: in the installation with multiple VFDs, the input power line of all VFDs can be in the same pipe, and the control line can be in the same pipe, but the output wiring of each motor must be in a separate pipe. The only exception is that if a VFD is used to operate multiple motors, the output wiring of all motors can be in the same conduit.

Use the driver on the grounding system. Do not use floating floor. Some manufacturers do not recommend floating input on any submicro or newer design drives. If there is no interference on the line, the driver should operate well - but severe common mode noise can cause a false trip or worse.

Note: some traditional VFDs use a string of resistors between the DC bus and ground, which means that common mode noise is not a problem. Some integral HP drives also use resistor strings, so using these floating grounds may not be a problem. However, floating point systems are not recommended for newer drive technologies.