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One proven method for discovering insulation integrity problems is to wait for a fault to occur. This can result in a spectacular fireball, and if you’re lucky yours will happen on the Fourth of July.
Unfortunately, massive fireballs tend not to add to a facility’s safety ambiance. Even if you don’t particularly mind that production comes to a complete stop, the safety problem is a real killjoy here.
Section 110.7 of the NEC mandates that completed wiring installations be free from short circuits, ground faults, or unintended connections to ground. Failure to comply is negligence, which can have ramifications for collecting insurance or defending against personal injury suits.
A better, safer way is to set up an insulation integrity program that consists of automatic and manual testing.
Automatic testing involves insulation resistance monitoring where appropriate. Evaluate your large noncontinuous loads for applicability. If the monitoring system doesn’t include auto-trending with alarms on deviations, you’ll need external trending. That might be done manually or via your distributed control system (DCS) or a PLC application.
Manual testing means setting up scheduled shutdowns so you can conduct insulation resistance tests on all cables that meet certain criteria (e.g., cables above a certain size, critical cables, all feeder cables, all buried cables). As with the automatic system, you need trending. If you don’t understand cable test data trending or don’t have the staff to do all the testing in a day or two, it’s best to hire a testing firm to do this for you.
Source: Mark Lamendola | Mindconnection