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March 10, 2009 A Penton Media Publication Vol. V No. 5

Maintaining for Energy Savings, Part 8

Electrical Troubleshooting Quiz

Bottleneck Motor Repairs, Part 5

NEC in the Facility

Enroll In EC&M University's Online Arc Flash Courses

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.




    Maintaining for Energy Savings, Part 8
    Power factor (PF) traditionally has been one of those “set-it-and-forget-it” things. The basic idea is that inductive loads cause vectors to shift in one direction, so you add capacitors to shift them in the other direction and consequently operate close to unity PF. But is that all there is to it?

    If your facility never adds, modifies, or removes equipment, then you probably can “set it and forget it.” For most facilities, however, such an approach is not practical and leaves money on the table. Plus, it can cost a lot of money.

    One solution: Add a power survey to your preventive maintenance procedures. A tech uses a portable power analyzer to determine PF and other quantities on each feeder, perhaps annually.

    A better solution: Set up your power monitoring system to monitor PF on each feeder. The power monitoring system essentially does the PdM/PM for you. Each time you correct PF on a given feeder, update the alarm setting accordingly. Follow up on the alarms to solve for low PF and for PF variations.

    Why are we talking about PF at the feeder level? If you correct it at the entrance, then you avoid the PF penalties from the electric utility. But that’s all you do.

    You may have PF of 99% at the service and only 77% at the load. This means the load has to draw significantly more power to do the same amount of work. You aren’t paying the higher rate per kWH, but you’re using far more kW each hour. Correct PF from the load toward the service — not the other direction and not at just the service.

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    Electrical Troubleshooting Quiz
    You’ve received a work order to investigate a motor that has been replaced three times in as many months. The supporting documentation includes the repair history.

    The first motor failure was attributed to overheating due to a consistently high current draw caused by low PF at the motor. PF capacitors were added when the second motor was installed.

    The second motor failure was attributed to “inadequate grounding.” The repair record doesn’t indicate how that was determined or exactly how that was solved. However, it does state that the grounding errors also caused the drive to fail and “ground less than 25 Ω, ground added.”

    Before you install the third motor, what should you do?

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

    Bottleneck Motor Repairs, Part 5
    One key to fast repairs is the ability to quickly determine what the repair action needs to be and what resources the repair action requires. When a bottleneck motor is down, every minute lost is revenue hit — that’s not the time to plan out the repair job.

    To reduce the amount of revenue lost, you should already have a set of standard repair “templates” on file. Each covers a repair procedure for a specific problem with that specific motor.

    These repair templates are variations of a basic repair procedure (in a Web-based maintenance system, these can be linked directly from a master repair document). Based on your troubleshooting guide for that motor (also developed ahead of time), you proceed to the repair procedure to which the troubleshooting guide refers you. The symptoms indicate the problem is X, so perform repair procedure B (which lists all of the relevant drawings and other information needed).

    Using these documents, a repair crew quickly can determine what went wrong, what repair actions to perform, and how to perform them. Because you’re using a standardized methodology, there’s no trial by error or other guesswork — you’ve done those things “offline” instead of during downtime.

    In our next issue, we’ll look at developing specific troubleshooting guides and their companion repair procedures.

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    NEC in the Facility
    Article 504 covers the installation of intrinsically safe apparatus, wiring, and systems in Class I, Class II, and Class III locations (defined in Art. 500.5) [504.1]. An intrinsically safe circuit is one that won't ignite due to spark or thermal effect of (flammable or combustible) material in the air, under prescribed test conditions [504.2].

    You’ll find those conditions prescribed in ANSI/UL 913-1997. What you need to know is that anything that’s “intrinsically safe” is listed as such. If you’re working on an intrinsically safe system, replace any “intrinsically safe” apparatus with listed apparatus.

    If it is part of an intrinsically safe installation, then you must install it per the control drawing(s) [504.10(A)]. You need to do any wiring per 504.20 and grounding per 504.50.

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    • Clarifying NFPA 70E and IEEE 1584 Requirements (April 9)
    • Impact of System and Operating Conditions on Arc Flash Energy Levels (April 21)
    • High Resistance Grounding and Arc Flash Accident Prevention (May 7)
    • Mitigation of Arc Flash Hazards Using Fuses (May 12)
    • Arc Flash Testing Updates (June 16)
    • Arc Flash Hazard Mitigation Case Studies (June 25)
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    Quiz Answer
    Answer to Electrical Troubleshooting Quiz
    It’s unlikely that the drive manufacturer recommended installing those PF correction capacitors. External PF correction generally does not work well with a motor drive. Those capacitors are probably why the drive and second motor failed. The best solution for PF correction at a motor is almost always an upgrade to a PF corrected drive.

    The note “ground less than 25 Ω, ground added” tells us someone misapplied 250.56. This NEC requirement has nothing to do with motors. Grounding a motor at all is a waste of time and materials, and driving a second rod is just more of the same waste. A motor is properly grounded when it isn’t grounded (connected to earth, see Art. 100 definition). Make sure the motor system is properly bonded (Art. 100 definition and Art. 250, Part V).

    Consult the drive manufacturer about PF correction. Removing the PF capacitors and upgrading the existing drive will probably prevent further failures.

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