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January 22, 2008 A Penton Media Publication Vol. IV No. 2


CONTENTS
Optimize How You Handle Spare Parts

Motor Maintenance Tip, Part 5

Electrical Troubleshooting Quiz

Reducing Repair-Induced Failures

NEC in the Facility

Safety

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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    Maintenance
    Optimize How You Handle Spare Parts
    Your company needs to reduce inventory costs, but you can't allow production to stall due to lack of a critical spare part. To balance these opposing needs:
    • Review the min/max on spare parts. Proper quantity levels may have changed, due to changes in sourcing, lead times, and quantities used. Some parts may no longer be necessary.
    • Reduce re-ordering. Get off the replacement treadmill of high-usage spare parts. Solve root causes of the failures that drive the re-ordering (thus raising min/max). Solutions can include everything from power quality improvements to equipment redesign (in consultation with the manufacturer).
    Caution. If repair logs show that only one component in an assembly fails, you may be tempted to reduce inventory costs by stocking that component instead of the entire assembly. Before you do that, determine whether downtime will increase because of the complexity of installing that component versus the assembly.

    Supplier tip. Focus on value, not price. Which supplier is a better bargain? The supplier who took your call at 2:00 a.m. and had someone there at 3:00 a.m. with the one critical fuse you needed, or the discount supplier you can't reach at night? Let your purchasing people know which suppliers provide added value and in what ways.


    Motor Maintenance Tip, Part 5
    Single phasing (loss of one phase of a 3-phase system) produces significant heat in the motor. If a motor is overheating for no apparent reason, check the current draw on all three phases. If one phase is near zero (the other two carry the load), then you have single phasing.

    The cause of the single phasing is probably a bad contact in the motor starter, but it could be something else. In one application, an open supply fuse combined with an inadvertent backfeed to create a single-phasing problem.

    Monitor for single phasing. Overload protection is not intended to protect against a single-phase condition (it could, incidentally, if it conformed closely to the motor's heat curve). However, you can buy standalone protection units that detect single phasing and provide an alarm or even shutdown action. Motor drives, soft-starts, and other motor monitoring/control equipment often have this functionality built in.


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    Repair
    Electrical Troubleshooting Quiz
    Line Three never exhibited any problems until the PLC that controls it lost an I/O card a few weeks ago. Ever since then, the line has displayed erratic behavior. Despite several programming changes, the problem remains. Your boss assigned you to get to the bottom of it. Where should you start?

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


    Reducing Repair-Induced Failures
    Does it ever seem that some machines are jinxed? Good thing you have Johnny Ace on hand. He can "get it running again" faster than anybody. But maybe he's a bit too fast. When you have a "one-thing-after-another" problem with any equipment, suspect the repair methods rather than the equipment.

    If you want to see whose repairs are causing failures, look at how people treat their tools while working. Some people wipe every tool before putting it away, and put away every tool unless they're using it. Other people scatter tools (and parts) everywhere while they work, and their tools are never clean. Which person do you think pays more attention to the details in making a repair? Which one do you think is less likely to leave a stray dollop of grease on a drive belt or leave a loose washer on a busbar?

    We constantly train people what to do. They use troubleshooting techniques, employ repair methods, follow written procedures, and apply skills learned in a classroom. Nevertheless, we tend to drop the ball on training people how to do things.

    NASCAR history buffs pay homage to Red Vogt, the great mechanic behind several legendary racers in NASCAR's early days. Vogt had a reputation as a mechanical miracle worker. Not only was he known for powerful engines that did not fail, but also for keeping his work area spotless -- the two are not unrelated.


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    Operation
    NEC in the Facility
    A pulping plant in Kentucky began to have a high rate of motor failures. When a consultant inspected the motor invoices, he noticed the failures were among the same few applications. Once an application received a replacement motor, the failure rate went through the roof.

    The replacement motors were sized properly and were the right design for the intended load. However, they violated 430.16 because they were normally vented. The environment was full of flying fibers, thus requiring a totally enclosed fan cooled (TEFC) motor.

    The FPN to 430.16 notes especially severe conditions may require additional measures. That was the case with one particular application in this pulping plant. After installing a vented shroud around the motor, the monthly "replacement drill" ceased to happen.


    Safety
    How do you identify the energy source(s) of a piece of equipment for purposes of lockout/tagout? Suppose you locate the electrical drawings for a large press and identify the breaker that supplies power to the drive motor. You lock the breaker open and tag it.

    This action, while essential, doesn't mean the press is de-energized. It merely means the drive motor is de-energized. Be sure to account for mechanical springs and hydraulic cylinders, which can store energy. Another energy source is position. On a press, for example, the top die can't possibly fall on you if it's already all the way down.


    Quiz Answer
    Answer to Electrical Troubleshooting Quiz
    Find the backup of the "pre-problem" programming, and restore the programming as your first step. This eliminates one set of variables. Programming doesn't change on its own, so doing programming mods doesn't solve for failure.

    You need to look at the work surrounding the I/O card replacement, which is when the erratic behavior started. The most likely cause is either a loose connection in the sensing loop or a damaged sensor. Walk down the control loop and look for what someone might not have put back together properly when simulating the input to that loop during the I/O card troubleshooting process. Find out who replaced that I/O card, and show that person what you found.


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