Electrical Troubleshooting Quiz

Last year, insulation resistance test trending showed that several cables needed replacing

Last year, insulation resistance test trending showed that several cables needed replacing. While scoping out the job, you determined it required two crews working two shifts to complete the work. Why would it take so much time to perform this type of work?

For starters, there was barely enough working room. Adjacent switchgear had to be de-energized, which required coordination with a second production department. Further difficulty arose due to the size of the cables combined with the distance from outside access points, plus limited room for staging the pull. Three production machines had to be disconnected and temporarily located out of the way.

Recently, two of those same cables have actually faulted. What might be wrong now?

Difficult cable pulls tend to end badly unless you're very thorough in preparation. Eliminate as many "gotchas" as possible by examining the installation area and noting where it can be improved. Add modifications (e.g., remove sharp edges) to the project scope.

Cables may have been damaged before the pull. Does the tight space mean operators walked on the cables? Or, maybe a lift truck drove over them. A transient event may have damaged those cables, so examine the history in your power monitor to see if a large transient occurred. If you don't have a power monitor, then this expensive cable replacement project can justify purchasing at least a mid-level system. Determine if your transient protection is adequate. Is it a proper multi-stage system, or do you just have a set of big MOVs at the service?

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