Throughout the plant, operators are reporting receiving shocks when touching metal raceway, metal conveyor structures, motors, and water fountains. The plant manager advised the production managers that operators shouldn’t be touching raceway or motors. But, he continued, those items are grounded so how anyone can be shocked is a mystery.
The plant engineer is a mechanical engineer, so he approached the problem mainly from that standpoint. He wrote a work order instructing mechanics to tighten all the ground connections and note any that looked corroded or in some other way compromised.
That project didn’t solve the problem. Now the plant engineer has asked you for input.
First, you never simply tighten grounding connections (or bonding connections either, and those are probably what was tightened). So now all those connections will have to be taken apart and replaced with new hardware so they can be eliminated from consideration in solving this problem.
The fact people are being shocked shows that undesired current is flowing through equipment rather than along a low-impedance path back to its source. To fix this, you’ll need to look for things like the building steel being used as part of the equipment grounding conductor (EGC) (a metallic path that is really a bonding system). Building steel presents many pathways through many connections of various impedance. It can’t serve as the EGC [See NEC Sec. 250.118]. Also, ensure continuity with anything that is part of the EGC.
