there is a 480v feed to a control cabinet that didnt have a groung pulled in the feed. This control cabinet controls variable fequency drive motors that trip from time to time. the fault indicator says that undervoltage has occurred. when we check voltage the voltage is good and we reset the VFD. We had the electrical contractor come back out and ground the control panel. they took a ground from the control cabinet to the building steel. My question is, is this sufficient or does there need to be a ground pulled in the feed conduit and why?