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April 6, 2010 A Penton Media Publication Vol. VI No. 7



CONTENTS
Cast Your Vote for the EC&M Product of the Year!

Insulation Resistance Testing, Part 4

Electrical Troubleshooting Quiz

Climbing the Corporate Repair Ladder

NEC in the Facility

Safety


About This Newsletter
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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    The designations "National Electrical Code" and "NEC" refer to the National Electrical Code®, which is a registered trademark of the National Fire Protection Association.

     
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    Product of the Year Competition
    Cast Your Vote for the EC&M Product of the Year!
    Would you like to help pick the prestigious EC&M Product of the Year winner and qualify for a chance to win $100? If you're an EC&M subscriber, make your vote count by visiting the 2010 EC&M Product of the Year category winners list. To review the products, click on the links for each of the 33 category winners to read a brief description and view a photo. Once you're finished with your review, visit the polling page, enter your contact information, choose your favorite product from the drop-down menu, and click submit.

    Your selection will help us identify the 2010 EC&M Product of the Year Platinum, Gold, and Silver award winners. As an added incentive, three lucky voters will be randomly selected to receive a $100 gift check.

    The voting poll will remain open through 5 p.m. on June 18, 2010. Please, only one vote per EC&M subscriber. Any votes received from manufacturers, PR firms, or non-EC&M readers will be discarded.


    Maintenance
    Insulation Resistance Testing, Part 4
    In our previous issue, we described time-resistance and dielectric absorption ratio tests. Two other useful insulation resistance tests are the short time and step voltage tests.

    • Short time. This is also called a “spot reading” test. It's a quick check that reveals gross defects in the insulation. Apply the test voltage for a designated interval, and then record the results. That interval is usually 60 sec. Though you can use any interval you wish, make your choice only once. Use the same interval consistently, so spot readings make sense when compared to "typical" readings.
    • Step voltage. Another name for this test is “tip-up.” It's essentially a spot reading done at one voltage and a second SR done at a higher voltage. Good insulation exhibits the same resistance reading at either voltage. If the readings differ, then there’s a problem with the insulation (e.g., pinholes, contamination).
    Always perform one of these tests before incurring the time and expense of installing a motor.



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    Repair
    Electrical Troubleshooting Quiz
    Every so often, your plant seems to lose motor drives in batches. Three weeks ago, four drives failed within a few hours of each other. Last summer, a similar incident happened on two different occasions with three drives the first time and two the second.

    You contacted the drive manufacturer, who asked you to send in two of the failed drives. You just got the report back, stating that the surge protective devices (SPDs) in both drives were fried.

    What could be causing this, and what should you do?

    Visit EC&M's Web site to see the answer.


    Climbing the Corporate Repair Ladder
    In many industrial systems, the repair process involves using ladder diagrams for troubleshooting. Unfortunately, these drawings frustrate many people in the field. However, if you understand a few fundamentals, then ladder drawings make sense and become easy to use.

    To read more on this story, visit EC&M's Web site.


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    Operation
    NEC in the Facility
    Don't confuse surge arresters (Art. 280) with surge-protective devices (Art.e 285). The main distinction the NEC makes is the voltage level: If it's more than 1kV, it's a surge arrester. Otherwise, it's a surge-protective device (SPD).

    This isn't an arbitrary distinction. A single device can't handle all voltage levels, due to those pesky laws of physics. Article 280 devices reduce voltages to levels that Art. 285 devices can handle.

    Use Article 280 devices where the higher voltage levels are encountered (e.g., on the service drop). These devices reduce large transient voltages, typically by diverting the “peak” of the transient to ground. An example is the spark gap device. The desired power does not pass through this device, but the undesired power does. In a piping system, the equivalent would be a pressure relief valve.

    Use Art. 285 devices where the lower voltage levels are encountered (e.g., on a distribution panel). These devices reduce smaller transient voltages by blocking or diverting the “peak” of the transient. Generally, the desired power does pass through these devices — they are in line with the flow of power. In a piping system, the equivalent would be a pressure control valve.


    Safety
    Think of how many intricate things you do with your hands just to wire a switch. How well do you protect your hands?

    Gloves are the standard PPE for hand protection. However, you must use the specific type of gloves that fits the situation. For example:

    • For electrical protection, wear gloves suitable to the energy levels involved. Test prior to use with the correct method (don't blow into them).
    • If you're using solvents, adhesives, or other chemicals, check the container label or Material Safety Data Sheet (MSDS) to find out which gloves to use.
    • Wear work gloves in situations where mechanical injury is possible. A slip with a saw can be a nonevent, or it can send you to the emergency room.


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