Q: We experienced an event that has caused some confusion among crew and supervisors about what we thought we knew about grounding. We were working midspan on a de-energized 345-kV circuit. We drove a ground rod, grounded our trucks to it and grounded the phases to it. Almost immediately, we smelled hot rubber, and then tires started to smoke. Can you help us understand why this happened?
A: That was likely much more serious than hot tires. For the benefit of readers, we spoke with you on the phone, got details and shared opinions. Here is what happened: Your crew was in a right-of-way with very high induction. The ground rod you drove was very high resistance. When you connected your trucks, essentially you made a radial connection from phase to truck through the ground rod connection. In doing so, you loaded very high induction current onto the truck, which passed into the earth across the tires and outriggers. Many utilities by procedure use ground rods at midspans, and often it goes without problems. This is why we stress learning the principles of current flow in grounded systems. If you can ground phases to the very low-resistance static, the induction load is handled without much risk to workers on the ground. If you do have to ground your truck, and there is high induction, a well-driven rod isolated from the phase grounds might be a good choice. If grounding to the same ground electrode as the phases can energize the truck, as happened in your case, dangerous gradients can occur around the truck, and touch potentials between earth and truck can be deadly.