To determine what the right maintenance is, you need to be keenly aware of which equipment is vital to product flow (making it "critical equipment") and what maintenance actions prevent breakdowns. Complicating matters is the fact that some product flow is more important than other product flow.


Repair
Electrical Troubleshooting Quiz
A 400A breaker has tripped four times this week. Your "secret weapon," the power monitor, has finally let you down. For some reason, it failed to capture any triggering events. What's going on?

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

More Downtime is Better?
The traditional view of maintenance is that less downtime is better, but this isn't always true. Sometimes, you should choose to allow more total downtime of production equipment. However, the company pays its bills by selling products. How can increasing overall downtime be anything but counterproductive?

The answer lies in the fact that resources are limited and not all downtime is of equal value. Let's use an example to illustrate how this works. The company makes Widget-A, Widget-B, and Widget-C.

• The profit on each Widget line is $120, $180, and $14, respectively.
• The average daily unit sales are 95, 70, and 8, respectively.
• The company can barely keep up with demand on Widget-A orders. It has a three-day supply of Widget-B units and a 10-day supply of Widget-C units.

On the other hand, don't lower yourself into the stew kettle. To stay out of hot water, ask the other production supervisors to meet with the Widget-C supervisor and review the numbers. Unless that Widget-C supervisor loves job hunting, you'll get the agreement you need. Nobody with common sense tells the plant manager, "I held down our total revenue to make my own numbers look better."


Operation
NEC at the Facility
Suppose you're adding a convenience receptacle at the operator station for a process control system. Per the installation manual, this system has its own ground rod. The drawing provided for the receptacle shows the receptacle grounding terminal wired to a bus that connects to that rod. Should you install per the drawing, or should you run a separate ground wire back to the panel where you connect the neutral and hot?

The receptacle needs an equipment ground, not an earth ground. An earth ground is for lightning protection. You can't use it for the receptacle ground. Run the separate ground wire. While you're at it, make sure that ground rod is bonded back to the power source. This will fix the many Article 250 violations that exist if it is not.

Unsafe Assumptions
Assume any of the following during an electrical test, and you may not live to conduct another:

1. "I don't need to check my test equipment unless there's a problem." It's a little late to inspect test equipment, especially test leads, after you've already been electrocuted. Check before you connect.
2. "All grounds are the same." An equipment ground is part of the bonding system, not the earthing system. Connect to the wrong ground, and you may be shocked at what you find -- literally.
3. "Nobody else is at risk if I inject a high voltage now." Verify that everyone is clear and that cables and equipment are properly isolated.

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Quiz Answers
Answer to Electrical Troubleshooting Quiz
Rest easy. Your trusty friend hasn't let you down. The power monitor has shown you that the failure isn't due to a triggering event. This narrows down your troubleshooting considerably. The cause is probably a worn mechanism inside the breaker. Because the frame alone is probably more than $1,000, consider the economics of having an authorized shop rebuild the breaker.