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October 11, 2007 A Penton Media Publication Vol. III No. 19


CONTENTS
Fine-Tuning Written Procedures

Circuit Breaker Maintenance Tips

Electrical Troubleshooting Quiz

Motor System Repair Mistakes, Part 3

NEC in the Facility

Safety Habits

Answer to Electrical Troubleshooting Quiz



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This twice-a-month
e-newsletter is brought to you from the publisher of EC&M magazine.

MRO Insider addresses topics such as:

  • Working with management and supervision
  • National Electrical Code® on the production floor
  • Safety procedures and programs
  • Troubleshooting techniques
  • Equipment maintenance and testing tips
  • Managing motors and generators
  • Trends in training and education
  • Managing energy use


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    Maintenance
    Fine-Tuning Written Procedures
    To have an effective and efficient maintenance program, you need good written procedures. Follow these four tips to tune up your approach:
    1. Review for accuracy against manufacturers' recommendations and industry standards.
    2. Review for usability, clarity, and conciseness.
    3. Seek and utilize user input.
    4. Include references to prints, manuals, and online resources.

    Circuit Breaker Maintenance Tips
    Lubrication should slip (that's what it does), but your circuit breaker lubrication schedules should not. Over time, the grease (which is the carrier for the oil) dries out and loses lubricity. Heat accelerates this process. Pressure is another enemy of lubrication, because you most need the lubricant in the very places where surfaces meet and squeeze it out.

    How this affects you: You depend on that breaker to open during a fault. Lubrication deficiencies will delay operation or prevent it entirely.

    What to do: Ensure your preventive maintenance (PM) program includes the manufacturer-recommended breaker maintenance, adjusted for your application.

    You can't perform PM on breakers without de-energizing them. This is why a maintenance bypass or dual-feed system is essential for critical equipment. To get funding for such items, calculate the cost of not having fault protection (including lost revenue).

    It's helpful to present costs for three scenarios of outcome: most likely, best possible, and worst. If that breaker fails, the most likely outcome is the fault will destroy the supplied equipment and cabling. The best outcome is the fault will destroy just that breaker. The worst outcome is the fault will cause catastrophic damage, resulting in widespread equipment loss and severe hazards to personnel. Unfortunately, "best-outcome" scenarios are rare, but "worst-outcome" scenarios are not.


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    Repair
    Electrical Troubleshooting Quiz
    A 50-hp drive motor failed on line three. Before going out to the line, you look at the PM history and pull up a graph. This graph shows a line sloping gently downward, left to right. Suddenly, the line "breaks" into a sharp downward turn. The date is one month ago.

    Ask yourself three questions:

    1. What chart are you looking at?
    2. What's wrong with that motor?
    3. What must you do to get line three running again?
    The answers to these questions appear at the end of this newsletter.


    Motor System Repair Mistakes, Part 3
    Skimping on "as-left" information may seem like an easy way to reduce work overload. However, the law of unintended consequences produces the opposite effect. This bad habit is one reason preventable breakdowns occur in the first place.

    Two compelling reasons to take complete and accurate "as-left" data include:

    1. You know what changed, making it easier to solve problems the next time.
    2. You can see a change during the next PM/PdM and take corrective action to prevent the failure from occurring.
    It's easy just to check off "OK" boxes on a PM/PdM form when you're in a hurry and nothing is obviously wrong. Taking a measurement means you have to get objective rather than subjective data. So, make sure PM/PdM forms require filling in actual values.

    The static (motor not running) "as-left" data should include:

    • Input waveforms (noted as "motor de-energized").
    • Insulation resistance tests.
    • Alignment data.
    • Condition of air filters, if applicable.
    The dynamic (motor running at operating temperature) "as-left" data should include such things as:
    • Input waveforms (noted as "motor running").
    • Bearing temperatures (simplify to "front" and "rear" rather than "load" and "thrust").
    • Vibration, expressed in engineering units.
    Of course, taking data takes time. Develop "as-left" requirements that meet your needs without being such a burden that people will cheat on data sheets. How? Update existing forms, one at a time, per the following:
    1. Identify items to add (use manufacturers' guides, industry standards, and equipment history as sources). Note why any particular item was added.
    2. Have maintenance personnel review step 1 results and listen to what they say. This increases compliance, and you get better PM/PdM forms.
    3. Prioritize and select. You can't afford to have people gathering every possible useful scrap of data, and they probably won't do it anyway. Pare down your form to something manageable. Collect only what is most important. Apply Pareto analysis, if you can't decide.
    Save time by using digital cameras to record nameplate data. A picture may be worth a thousand words, but it's also faster and more accurate than re-keying information into a PDA or scribbling onto paper.

    It's always a good idea to use a heat gun to take bearing temperatures. Even better, you can use a thermal imaging camera to get an entire temperature profile.


    Operation
    NEC in the Facility
    Do you consider your fixed electric space heaters to be periodic duty loads? Article 100 defines a periodic duty as intermittent operation in which the load conditions are regularly recurrent. Heater use recurs regularly each winter, so what would your answer be?

    Answer carefully. Article 100 also defines a continuous load as one expected to run at maximum current 3 hours or more. Whether something runs seasonally or not is irrelevant. When it's running, your distribution system needs to be able to carry that load. This is why 424.3(B) says branch circuits for fixed electric space heaters are continuous loads.


    Safety Habits
    After a scorching summer, most of us are happy about cooler fall temperatures. However, there's something uncool that happens each fall. When it's crisp but not cold, people wear light jackets and "windbreakers." These are typically made of material such as polyester that melts into your skin if it catches fire. Don't wear such items around electrical equipment.

    Caution: "Microfiber" is polyester. Wear a jacket suitable for electrical work or no jacket at all. You can find proper apparel wherever electrical supplies are sold.


    Quiz Answer
    Answer to Electrical Troubleshooting Quiz

    1. It's the winding insulation resistance chart, trended over time.
    2. That downward break in the slope means the insulation has accelerated its normal deterioration, and a problem is going to happen soon.
    3. This motor has a failed winding. For this size of motor, that's rarely a "repair-in-place" situation. Thus, the motor needs to be replaced.


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