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When VFD Cables Aren’t Used, You Can Face Premature Motor Failure


Do you know the significance of using VFD cables and the impact they can have on your operation’s efficiency? Did you know that drives have issues that traditional power systems don’t? Traditional power is 60 hertz, three-phase power, and for the most part that works well because it just uses a simple single frequency of 60 hertz. Drives have hundreds of thousands of frequencies involved in the pulse with a modulated waveform that a drive puts out. These frequencies can be over 30 megahertz, so it’s roughly a million times higher in frequency. This high-frequency information makes electricity work differently. Currents like to flow on large surface areas and not through the body of a single conductor. They will flow on building infrastructures like large steel, and it changes the game. You need a special cable between your inverter and motor to be able to handle these effects. When VFD cables aren’t used you can be faced with premature motor failure primarily through bearing fluting which damages the bearings. Electromagnetic interference is another big factor that can affect radios, communications, and control systems. You can also have drive trips which can lead to excessive drive trips when you use the wrong cables. Motor failure is also another possibility, so there are a variety of issues you face when VFD cables aren’t used with your motors and drives.

An example of how using the wrong cable can impact your production is using an unshielded cable to run your drive. This can cause electromagnetic interference and trip your fire alarm system causing you to have to shut down production, evacuate the building, and figure out what the safety issue is. If you’re lucky you figure it out the first time, but if you don’t you could potentially have to keep starting and stopping your production line until the fault is found.

To help alleviate potential problems in the future, VFD cable is one of the first things you should look at when setting up your motors. When you do this a few issues will be addressed. When a shielded cable is properly installed it will significantly reduce EMIs. Drive cable needs to be terminated differently than other cables because drives create a lot of common mode current, which is excessive current that gets pushed down to the drive or pushed down the cable from the drive to the motor. Once the current is down with the motor it can’t just sit there it has to go back to the drive. Because the current is high frequency it is unstable, and you don’t know where that current is going to go. When a properly terminated VFD cable with a low impedance termination and high frequency at both ends is used, now we have a path for the current to flow back to the inverter. By minimizing all the current flows you’re going to reduce problems. By properly terminating the cable’s shield you also get the benefit of EMI mitigation so you aren’t broadcasting noise throughout your facility that can interfere with other processes. If doing this can take one drive trip out of your process, isn’t it worth it?

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