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July 24, 2006 A Prism Business Media Publication Vol. II No. 14

Maintaining the Motor Environment,
Part Three

Electrical Troubleshooting Quiz

Upgrading Motors

NEC at the Facility

The Practical Implications of OSHA 1926.417

Answer to Electrical Troubleshooting Quiz


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  • Troubleshooting techniques
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    Maintaining the Motor Environment,
    Part Three

    Why do motors run? To drive loads. If you haven't looked closely at the load, you've overlooked a significant cause of inefficiency and premature motor failure. Motor maintenance doesn't stop at the output shaft. At a minimum, examine these areas:
    • NEMA design/load type match. Check your motor data to see if the motor is a NEMA Design B, C, or D. Then, determine your load's requirements for starting torque, locked rotor current, and breakdown torque. A mismatch here is costly. It won't hurt to consult your distributor or manufacturer for assistance.
    • Alignment. Ensure the motor output shaft and load input shaft are properly aligned in three dimensions. Laser alignment and vibration analysis are the standard tools for this. If the alignment is fine but you have vibration, inspect the couplings.
    • Gearbox lubrication. Electronic drives control motor speed. But it's common to use a gearbox on the output side to multiply torque. To the motor, this gearbox is the load. Check the gear lubricant on a periodic basis. Also, determine if you are using the best lubricant for the application. In one factory, changing from regular gear oil to synthetic dropped the temperature of each gearbox by about 40°F.
    • Miscellaneous load issues. In your motor maintenance procedures, add the task of visually inspecting the load. Ask for load-specific measurements. Those might include coolant temperature, running speed, output pressure, and so on. The idea is to record and trend values so you can quickly spot deviations. If the instruction is simply "Conduct visual inspection of the load," you won't get useful information. If the data collection is redundant with other efforts, consider that there is little cost to taking a few more data points during motor maintenance and doing so may show you impending failures at their earliest, most preventable stages.

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    Electrical Troubleshooting Quiz
    Those process exhaust fans seem to fail on a regular basis in the summer -- when they are needed most. What are some key trouble points?

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

    Upgrading Motors
    Sometimes, you find that the original motor wasn't appropriate for the application. So, you upgrade. To many people, this means replacing the motor with one of the next higher horsepower models. But that can lead to even more problems.

    For example, perhaps the old motor pedestal isn't strong enough for that larger motor. So after the replacement, you get deflection and vibration.

    Many times, the answer isn't "a bigger motor." The answer could be a motor with better insulation for thermal characteristics -- or one matched to that particular motor drive. Before you upgrade a failed motor:

    • Determine the cause of failure. A motor shop can do a post-mortem to help you determine this.
    • Perform a thorough analysis of the application to determine the motor requirements.
    • Present findings from both efforts to your electrical distributor or motor manufacturer for a recommendation.
    Yes, you incur additional cost with the motor shop work, and you'll have to spend extra time doing the research. This extra cost and effort may tempt you to just guess "next size up." Anybody can make guesses. To do the job right, get the facts before you make the purchase.

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    NEC at the Facility
    Ensuring Chapter 3 conformance is a fundamental part of solving many electrical problems. The primary focus of Chapter 3 is the correct sizing and installation of conductors, raceways, and enclosures.

    A common Chapter 3 error is the use of the wrong ampacity table. To prevent this error, carefully read the short description at the top of each Table.

    Chapter 3 is easier to understand when you group the Articles into these categories:

    • Wiring methods (300)
    • Conductors (310)
    • Enclosures (312 and 314)
    • Cables (320 -- 376)
    • Raceways (378 -- 392)

    The Practical Implications of OSHA 1926.417
    The subject of lockout/tagout is a source of confusion for many people. Suppose you place a lock, but no tag, on a breaker. Then, you finish the work and forget about the lock. On the next shift, someone -- after asking around and not finding out who put the lock there -- cuts off your lock. No harm done, other than the cost of your lock. But this is a very dangerous game to play.

    OSHA requires you to apply both a lock and a tag. One without the other might protect you. But why gamble?

    To work safely:

    1. Walk down the entire path of energy for the circuit you are working on.
    2. Move controls to the de-activated position, and tag them.
    3. De-energize equipment, then lock it out so it cannot be energized.
    Affix your tag showing what is locked out and who locked it out.

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    Quiz Answers
    Answer to Electrical Troubleshooting Quiz
    This quiz ties together several concepts. Here are some places to start checking for the cause of those failures:
    • Exhaust fans normally require NEMA Design B motors, but if your process exhaust fans have to blow through filter bags, you might need NEMA Design C motors due to high inertial starts. Ask your filter system rep. for a review of your system specifications.
    • The filter bags might be under-maintained. If you don't have differential pressure instruments across those bags to alert you when the bags need changing, your motors may have a much heavier load than necessary. In the summer, the air is also more likely to contain particulates, causing you to use up filter capacity faster.
    • In the summer, with its higher ambient temperatures, the motor might not have insulation sufficient for the temperatures in which it's operating. Use a thermal gun to take temperature readings at and near the motor, during peak heat times. Consider upgrading to a motor with a higher temperature rating.
    • If the fans are belt-driven, check the belt tension and alignment.
    • Summer and winter lubricants are different. If the motors are subject to summer and winter temperature changes, the lubricant may be too thin in the summer -- allowing metal on metal contact. Too thick a lubricant also causes problems.

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