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July 22, 2008 A Penton Media Publication Vol. IV No. 14

Maintenance Management

Motor Maintenance Tip, Part 17

Electrical Troubleshooting Quiz

Response Speed

Fuses and Motors

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


    Maintenance Management
    How well do you perform these three critical functions in maintenance?
    1. Qualifying personnel. OSHA and the NEC both provide definitions of “qualified.” In a nutshell, a qualified worker has the necessary training and experience to competently (and thus safely) execute the assigned task on specific equipment or systems.
    2. Providing procedures. Good procedures outline the major steps and identify the critical ones. They provide cautions, references, and advice (one common approach is to tie these to “stop points”). Don’t use generic cautions — provide cautions on working with the safeguards, interlocks, and alarms for that particular equipment. Your procedures should identify any special needs in test equipment, tools, PPE, or materials. They should identify special precautions (e.g., venting), permissions needed (e.g., operations supervisor), and permits needed (e.g., confined space) for the specific tasks involved.
    3. Reporting. Reports on completed work need to show “as found” (measurements and other data pertaining to the equipment condition), work done, test equipment used, and “as left.” They should include observations (e.g., breaker meets specs, but operation was stiff) and recommendations (e.g., breaker needs inspection before normally scheduled next inspection to see if exercise and lubrication fixed the problem). Every report form should include a space for safety concerns and problems encountered (e.g., guard missing on cutter, key didn't work, had to move clutter from in front of switchgear).

    Motor Maintenance Tip, Part 17
    Proper bonding at the motor is critical, but there is no reason whatsoever to ground at this location. The best possible earth ground won’t provide a low-resistance path that prevents flashovers or currents from circulating through your bearings. That’s what bonding [Article 100] is for. Grounding does neither of those things.

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    Electrical Troubleshooting Quiz
    A mixing system under PLC control experienced oscillations and then process runaway on the backshift. Now, a few hours later on dayshift, the system is responding sluggishly and scrap rates are high.

    You consulted the logbook and found the responding technician merely noted, “Adjusted program. Stopped and restarted system. Monitored for oscillation, but found none.”

    Two questions:

    1. What is wrong with that log?
    2. Where do you start to determine what is wrong with this system?

    The answers to these questions appear at the end of this newsletter.

    Response Speed
    Which maintenance tech effectively responds faster to a conveyor failure call?

    1. Tech No. 1 arrives in 30 seconds with a screwdriver and pliers.
    2. Tech No. 2 arrives after first going to the shop to obtain a tool pouch, DMM, and the applicable repair procedures.
    • A screwdriver used for any purpose other than turning screws is dangerous and inevitably becomes worthless as a screwdriver.
    • Changes made without “as-found” and “as-left” measurements defeat any effort to know the problem is actually fixed.
    • Unless Tech No. 1 resorts to the “wing-it” method, Tech No. 1 will walk to the shop and back for the needed tools, so he or she is actually slower than Tech No. 2.

    Fuses and Motors
    You need to account for the type and class of fuse when selecting the current ratings of fuses for individual motor branch short-circuit protection. Use Tables 430.248, 249, and 150 to select the correct fuses.

    NEC in the Facility
    In the typical facility, there’s an ongoing battle for adequate equipment closet space. One of the casualties of this battle is the distribution transformer.

    The unlucky transformer is often jammed into a small room. Open the unventilated door, and the heat just rolls out. Sometimes, the transformer vent faces the back of a cabinet or some other obstruction placed there after installation “to save space.” That condition can lead to a catastrophic failure that opens far more space than intended — complete with smoldering trails of vaporized metal.

    How can you argue persuasively for adequate ventilation? And how much is adequate? Most facilities are insured. Insurers nearly always require conformance to the applicable standards. For transformer ventilation, that is 450.9 of the NEC. In 450.9, you’ll find how much ventilation is adequate and other related requirements.

    But the 450.9 requirements are only the minimum for safety. They do not address efficiency. In this era of green initiatives, adequate ventilation is not enough. It’s likely, however, that the incremental increase in ventilation to produce the desired energy benefits isn’t much. Start with 450.9 and look for inexpensive ways to optimize ventilation from there.

    Your safety responsibilities probably extend to people who don’t even work for your company — such as visitors to your administration buildings or children who trespass onto your company’s property. So:

    • Secure doors and gates.
    • Secure mechanized equipment, power tools, vehicles, and toolboxes.
    • Lock carts and vehicles, and remove the keys.
    • Lock out unused circuits.
    • On energized circuits, coordinate with the engineer in charge of each system to apply breakaway locks as needed.
    • Erect proper barriers and signs.
    If your facility is near a school or apartment complex, look for bent fencing and other signs of entry. If children are nearby, consider a “talk with the kids” event so kids understand why they need to play elsewhere. The local police department is an excellent resource for this purpose.

    Quiz Answer
    Answer to Electrical Troubleshooting Quiz
    The answer to the first question is easy. That technician didn’t leave any data (e.g., “as found” or “as left”). The notes on the “repair” aren’t clear, either. What was the programming change? Why was it made? Your first step will be to do the documentation the night shift tech should have done:
    1. Take as-found measurements. Measure the applicable variables (e.g., input sensor levels, voltage supply, controller output) called for in the repair procedure (or PM procedure) for that system.
    2. Document programming changes. Compare the new programming to the original and record the differences.
    The program of a PLC system doesn’t “go bad,” so changing the programming when there hasn’t been a configuration change is almost always a bad idea. A programming change may disguise a problem temporarily, but it’s not a fix. So, restore the original programming. Then, check the inputs and the final control elements — where you will likely find the culprit.

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