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February 9, 2010 A Penton Media Publication Vol. VI No. 3

Fuse Maintenance, Part 2

Electrical Troubleshooting Quiz

Make Procedures Helpful, Part 4

NEC in the Facility



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    Fuse Maintenance, Part 2
    A good fuse maintenance procedure has two parts:
    1. Maintenance while energized:
      • Infrared scans of all connections, especially fuse clips.
      • Voltage checks across fuses (not necessarily right at the fuse).
    2. Maintenance while de-energized:
      • Insulation resistance tests of wiring and fuse holders.
      • Resistance measurements through connections and fuses. For control fuses, you can use a DMM. For power fuses, use an appropriate AC resistance tester.
    Both parts include visual inspection for corrosion, discoloration, or deterioration.

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

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    Electrical Troubleshooting Quiz
    Your company recently acquired another company's manufacturing facility. The previous management had cut costs by replacing experienced maintenance techs with recent tech school grads. Your boss sent you to solve an equipment problem that has dropped production to 40%. The problem is poor speed control on the main line, with symptoms ranging randomly from speed surges to nearly stopped.

    The line has three 50-hp drive motors controlled by VFDs. Over the past two years, each VFD has been replaced at least three times. The repair records contain some voltage measurements and a long list of "drive adjustments."

    How can you accomplish the mission your boss gave you?

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

    Make Procedures Helpful, Part 4
    In our last issue, we discussed using a diagnostic flow chart. This doesn't work for all systems or all organizations. An alternative approach is to do sequential testing against a series of possible causes (Check for A, if not A then go to B, etc.). The key to making this approach work is to limit the number of causes to be checked. How can you decide which ones to include?

    Make a spreadsheet and list eight to 12 failure modes across the top (you can pull these from your repair logs). Include an "Other" column. Now comes the tricky part. You need to sort these from most likely (on the left) to the least likely being (on the right). One way to do that is to have several senior repair techs rank these based on their judgment. For example, the most likely gets a 1, next most likely a 2, and so on.

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

    NEC in the Facility
    In our previous issue, we showed that Art. 516 is not as complex as it appears. Essentially, you choose from three options. After you make your choice, however, you have three additional possibilities to consider. Sections 516.3(D), (E), and (F) tell you to do the following:

    1. If equipment is within a Class I location, then apply the requirements of 516.4.
    2. If equipment is not within a Class I location (or a Class II), then apply the requirements of apply 516.5.
    3. Read through 516.10 to see if any of the equipment you’re working with is considered "special equipment."

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

    Stick your finger onto something hot, and you immediately pull it away because it hurts. Unfortunately, we can't rely on pain to tell us when our hearing is being injured. The damage is typically minor and painless at the time. Nevertheless, the damage is permanent and cumulative.

    It's better to wear earplugs than to wish, years later, that you had worn them. Remember this when you operate a lawnmower, snow blower, or even a stereo.

    Earplugs filter out certain frequencies, rather than simply dampening all sound. This provides a safety and productivity bonus. Earplugs allow you to hear conversation better in a high-noise environment. This means less chance of misunderstanding other people, which improves your job performance and your safety.

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