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April 8, 2008 A Penton Media Publication Vol. IV No. 7

Reports 101: Make Use of Graphics

Motor Maintenance Tip, Part 10

Electrical Troubleshooting Quiz

Reconfigure for Efficiency

Clear Up Current-Limiting "Con-fuse-ion"

NEC in the Facility


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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    Reports 101: Make Use of Graphics
    Your maintenance reports may contain all of the information required to justify downtime windows, budget requests, expanded testing programs, and training. But if people don't understand the information, the reports won't matter.

    Why might people not understand? Because:

    • They are skimmers, not readers. Managers are almost always skimmers.
    • They don't have your technical background. What is obvious to you may be Greek to them.
    • The key points don't stand out. They're lost in a sea of details.
    The solution? Use graphics to emphasize what's important. Your computerized maintenance management system (CMMS) makes this surprisingly easy.

    First, decide the top five points to emphasize. Look at output increased due to X, costs reduced due to Y, and so forth. Pick the five (more is usually not better) with the greatest financial impact.

    Export the relevant data from the CMMS to an Excel workbook. Then, select a chart format that most clearly shows the information that supports your intended point. A Pareto analysis makes this especially compelling. In our next issue, we'll examine how to do that.

    Motor Maintenance Tip, Part 10
    Overheated motors use more energy and fail sooner. The most easily corrected cause of motor overheating is often the most neglected cause: restricted ventilation.

    Keep motor vents clean to maintain required airflow. How often you need to clean the vents depends on how dirty the environment is.

    To develop an accurate cleaning schedule, you must first establish baseline data. Begin by taking "as-found" data. Conduct a walking tour and:

    • Use a thermal camera to determine the motor temperature profile.
    • Note which motors have dirty vents.
    Clean the dirty vents, wait a day, and take new thermal readings. You now have baseline data you can compare with "as-found" data on future inspections. Add vent cleaning to your PM schedule, adjusting the interval per thermal imaging. Some motors might require vent cleaning weekly, others only quarterly.

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    Electrical Troubleshooting Quiz
    Last summer, the main drive motor on an important piece of production equipment would simply stop in the middle of the afternoon. Restart wasn't possible for a few hours. This affected delivery on the customer's orders for whom your company bought that equipment. Your plant manager just received an e-mail from that customer's purchasing manager wanting to know your company's plan for preventing a repeat of last summer's late deliveries. Absent a solid plan, they will find another supplier. How can you solve this problem?

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

    Reconfigure for Efficiency
    The configuration of a "vendor skid" or equipment assembly makes perfect sense at the factory but may not be optimum for repairs in your specific application. Similarly, a contractor may install equipment correctly but sub-optimally for facilitating repairs. Something as simple as moving a PLC panel 8 inches to the left to allow room to swing the lift's boom in a specific path may save precious minutes.

    You can reduce repair time by assigning someone to analyze a repair in progress and determine how configuration changes can reduce the time to perform specific steps -- or even eliminate those steps. An industrial engineer does this to improve efficiency of production. You can do it to improve efficiency of repair.

    Clear Up Current-Limiting "Con-fuse-ion"
    People sometimes refer to "current-limiting fuses." How are those different from other fuses?

    A fuse is an overcurrent protective device that contains a calibrated current-carrying member. Under the overcurrent conditions it's calibrated for, that member melts and opens the circuit.

    A current-limiting fuse is calibrated to limit the duration and magnitude of the current flow under a short-circuit condition within its current-limiting range (the range of short-circuit currents the fuse will clear in less than ½ cycle). The upper part of this range is the maximum interrupting rating.

    NEC in the Facility
    Automation is a great thing, but it has its limits. One such limit is the automatic restarting of a motor. The NEC prohibits this if the restart can result in injury to people [430.43].

    Interpret this prohibition strictly. Another way to say it is this: If there's any way a restart might harm a person, don't automate it.

    Good candidates for automatic restart include plant air compressors and HVAC systems. With production equipment, the possibility of injury or equipment damage usually makes this a bad idea.

    Do you review safety information for completeness, accuracy, and applicability? Doing so may spare you months of agonizing therapy -- or worse.

    Sure, your supervisor has the responsibility of giving you safety information for any work you perform. Your supervisor is supposed to find out what hazards may arise from that work, and determine the means you can use to protect yourself.

    But supervisors, being human, make mistakes. Do you want to personally pay for someone else's mistake? Probably not. Help your supervisor and yourself by methodically reviewing the safety information your supervisor provides. One way to do this is to "walk through" the work. At each step, ask, "What are the possible dangers I could encounter?"

    Quiz Answer
    Answer to Electrical Troubleshooting Quiz
    The timing is a great clue. Even the customer realizes this is a "summer issue." It's possible you need a different motor. However, before going through that expense, you need to look at the conditions in which the existing motor operates.

    Because heat is part of the problem and ventilation is how you remove heat, your first step will be to implement this newsletter's Motor Maintenance Tip (Part 10). Last summer, the motor repeatedly operated past its heat limit and shut down. Determine how close that motor is to its heat limit now, when ambient temperatures are lower. If the motor is "down in the guts" of the equipment, adding a duct to supply filtered air from a cooler location may solve the heat problem.

    Check the motor to see if its insulation rating is appropriate for the thermal conditions. Consider using a larger motor (more torque means the motor doesn't work as close to its limits) with motor speed controlled by an electronic drive (consult your motor manufacturer for selection assistance).

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