The answer to this question appears at the end of this newsletter.

Planning Plant Maintenance Repairs
How is this for embarrassing? You arrange for a two-hour shutdown to replace a nuisance breaker that supplies a main feeder circuit. After closing the breaker and restarting production, everything works fine on that feeder. But another breaker in that same panel now won't reclose.

All kinds of similar situations have made sharp maintenance people look like chumps. Why does this happen?

We've all been taught, "If it works, don't fix it." We have a tendency to limit the scope of a repair to the item that caused us to fight for every hour of downtime to make the repair. This doesn't always work in our favor.

If you need to replace a breaker in Panel A, it usually does not make sense to start tearing into Panel B also. But if you have to shut down Panel A to replace a breaker, logic dictates that Panel A may have other problems. The cost and hassle of multiple shutdowns is far greater than just extending the Panel A shutdown for a complete checkup and preventive maintenance.

But you can take "full maintenance" too far. Trying to cram every conceivable test and task into a limited time slot by piling people and equipment into a limited space is asking for trouble. Instead, take these steps:

• Assess your time constraints. If the shutdown is occurring on systems that don't run 24x7, timing the shutdown to coincide with normal downtime or even shift changes may give you a larger window. Consider also any outages that are already scheduled.
• Assess the maximum crew size. This is a critical step many planners overlook. There is only so much space in a given work area, and you can't have people working on top of each other.
• Assess what is most critical. Yes, it would be nice to check off the box that you cleaned the cabinets. But breaker testing may be a more productive use of what little time and space you have.
• Consider the next downtime window. This is a subset of the previous step. Assuming any repairs will need another downtime window, what tests can and should you perform to identify problems to fix then? Factor in any lead times for ordering parts.

But what if your drawing ends up being a parallel circuit? Simply apply Kirchoff's Law. In essence, it says that electricity will flow in inverse proportion to the paths presented to it. To shunt more undesired current, bond to get that lower resistance path in parallel with the equipment or people you are trying to protect.


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Quiz Answers
Answer to Electrical Troubleshooting Quiz
The fact the loads are all drawing too much current is a classic sign of low power factor, although high harmonics may be the culprit. You need more information before changing anything. Use a power analyzer to determine the actual power factor and harmonics level on each feeder and at the service. If the problem is recent and seems to have occurred all on its own, suspect failed PF correction capacitors.