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February 10, 2009 A Penton Media Publication Vol. V No. 3

Maintaining for Energy Savings, Part 7

Electrical Troubleshooting Quiz

Bottleneck Motor Repairs, Part 3

NEC in the Facility


Answer to Electrical Troubleshooting Quiz

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This twice-a-month
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MRO Insider addresses topics such as:

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  • Troubleshooting techniques
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  • Managing motors and generators
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    Maintaining for Energy Savings, Part 7
    If your motors are properly mounted and correctly aligned, you’ve eliminated a major cause of motor energy waste (and a contributor to premature failure). If you have a well-planned and well-managed motor maintenance lubrication program, then you’ve eliminated a common cause of motor failure and energy waste.

    Where else can your motor maintenance efforts save energy? Let’s start with grounding. Are your motors grounded? If you answered yes, then you have a problem. Your motors should be bonded, not grounded (see Art. 100 definitions and Art. 250 Part V).

    Let’s examine three related areas for motor energy savings:

    • Bonding. Are your motors adequately bonded? Over time, bonding jumpers corrode, connections come loose or fail, and parts get broken. Your PM system should include a PM for visual inspection of the bonding system for each motor, at least annually. This would be in addition to the entirely separate maintenance tasks related to electrically testing the entire bonding system.
    • Power quality. Although harmonics and power factor are important aspects of power quality for motor energy savings, the most important aspect may be voltage imbalance. A 3.5% voltage imbalance brings about a 25% rise in temperature, which means waste heat. This additional heat also promotes premature motor failure. A good power monitoring system can let you know when it’s time to fix a power quality problem, so you can keep motors running efficiently.
    • Cooling. Establish a program to keep motor filters clean. You may need to replace existing filter setups to make this feasible. For example, replace screen mesh canisters with something easier to maintain. Contact a filter supplier for ideas.
    How are these three areas related? Proper bonding eliminates many power quality problems. Good power quality maintenance practices result in less waste heat being generated in the motor, whether from harmonics, voltage imbalance, or some other cause. The more you do to eliminate heat-causing power quality problems, the less work the cooling system has to do.

    Maintain the cooling system so that your other energy-savings efforts aren’t wasted and vice-versa. You may need to go beyond maintenance and make some design changes, if the motor runs hot despite having a clean filter or being a Totally Enclosed Fan Cooled (TEFC).

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    Electrical Troubleshooting Quiz
    The drive motor for a key production line trips its thermal overloads at least once a week. However, it didn’t start doing this until winter, and the trips always happen on second shift. The maintenance techs take voltage readings and perform insulation resistance tests but never find any problems. Nor do they encounter any problems with the restart. Something’s wrong, but what? How can you isolate and solve this problem?

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

    Bottleneck Motor Repairs, Part 3
    Previously, we discussed how to identify bottleneck motors. These should get the highest priority for repair and should receive the highest priority for implementing measures that reduce repair time.

    Using your bottleneck motor repair history and the manufacturers’ literature, determine the most likely repairs and the most time-consuming repairs. Then, make a list of the top three of each. A longer list is counterproductive.

    If you correctly anticipate the key things that can go wrong, then you can make effective plans to handle them. In our next issue, we’ll discuss the planning part.

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    NEC in the Facility
    Class II locations are those that have (or may have) combustible dust in quantities sufficient to produce explosion or ignition 500.5(C). Class II (and I and III) locations may be Division 1 (normal operations) or Division 2 (abnormal operations).
    • Use Division 1 wiring methods when combustibles are present under normal operations [502.10(A)].
    • Use Division 2 wiring methods when combustibles are present under abnormal operations [502.10(B)].

    Seal requirements for Class II locations [502.15] are simple, unlike the highly detailed requirements for Class I locations [501.15]. To avoid confusing Class requirements, remember that as the Class number rises, the particles become larger (I is for gases, II is for dust, III is for fibers) and thus easier to contain.

    Grounding and bonding requirements for Class II locations are in 502.30. Grounding doesn’t create an equipotential plane, but bonding does. See the Art. 100 definitions.

    "Misconduct" generally means willfully doing something you "should" know is wrong. The "should" part can be a gray area, but that doesn’t mean the penalties imposed are weak. Misconduct can result in a "sentence" not handed down by any civilized court, such as being horribly burned by an arc blast. Misconduct is a charge that can result in serious consequences even if you didn’t violate a specific rule. You can be fired, sued, and prosecuted for it. The "reasonable man theory" is a concept in our legal system that says everyone must meet reasonably expectable standards of behavior, even if no written rule covers a particular action.

    Because you can’t appeal to the laws of physics, always ask, "What must I do to be safe in this situation?"

    Quiz Answer
    Answer to Electrical Troubleshooting Quiz
    Look at power quality monitor logs to see if there’s some power event associated with the motor trips. For example:

    • Perhaps there’s cleanup work that involves running the big trash compactor at the end of first shift, thus causing waveform distortion. This could work the motor harder — possibly enough to overheat it.
    • At shift change, many people enter and exit the plant. Perhaps this brings in enough cold air that the plant’s electric heaters stay on too long and drag down the distribution voltage sufficiently to cause the motor to overheat.
    Inspect the area around the motor for what has changed. For example, maybe operators moved supplies from an area that was too cold for them to an area that’s warmer but blocks airflow to the motor.

    Perhaps the fact it’s winter is coincidental. Consider the production line itself — has the process or product changed such that the motor now has a heavier load? If the motor drives a gearbox, maybe there is not enough lubricant or the lubricant needs changing.

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