It’s been a few months since your last shutdown, and during that shutdown a testing firm conducted insulation resistance tests on all of your feeder cables. A few had to be replaced. But over the past couple of weeks several other cables have failed. These were designated as OK by the testing firm. The plant manager asked, “What are we paying them for if these cables fail anyhow?”
How can you begin formulating a good, factual answer to that question?
If the testing firm’s technicians are certified (for example, per ANSI/NETA ETT Standard for Certification of Electrical Testing Technicians), it’s unlikely they did anything wrong.
Insulation Resistance (IR) testing predicts cable failure based on conductor insulation deterioration over time. But it can’t catch everything before a failure. You obviously need additional maintenance tools.
Excess current, transient events, corrosive agents, insects, rodents, extended hot weather, and other factors can acutely damage conductor insulation. Look at such possible factors, not just IR results. Start by tracking power events with a power monitor; then you can follow with IR testing on the affected conductors. If you don’t have a vermin control program, have your facility inspected.
