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September 23, 2008 A Penton Media Publication Vol. IV No. 18

Circuit Breaker Dynamic Testing

Tie Breakers and Maintenance

Electrical Troubleshooting Quiz

Motor Repair, Part 2

Fuses and Capacitors

NEC in the Facility

Why You Should Report Any Injury, Part 2

Answer to Electrical Troubleshooting Quiz

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This twice-a-month
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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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    Circuit Breaker Dynamic Testing
    Sometimes in the course of breaker maintenance, a technician opens a breaker but can’t close it again. Consequently, the loads on that breaker are no longer available for operation.

    The typical production manager may react by saying something like, "We were running before you fixed things. Now we can’t run." Although this is technically a correct observation, it implies maintenance created a breaker failure — not merely discovered it.

    Consider the alternate scenario. You are able to close a faulty breaker, and assume that means you can leave it in service. Then, a fault occurs and the breaker fails to open. The reality is that not being able to close a faulty breaker is much better than being able to close it only to burn the plant down a few days later. And it’s better than finding yourself in court listening to a forensic engineer describe a problem you should have caught.

    Therefore, don’t return a breaker to service just because you can. You need assurance it will open on a fault. A key to making that happen is to operate the breaker multiple times, both mechanically and electrically. How many times is enough? That's a judgment call, but certainly more than once or twice. Go with at least the minimum recommended by the manufacturer, and test all methods of opening and closing.

    When operating the breaker manually (with no power applied to the breaker), observe the mechanism for binding, and observe the contacts for bounce.

    If you outsource your breaker testing, hire only a qualified testing firm. Before commissioning the work, review the testing plan against the manufacturer’s recommendations and resolve any differences.

    Tie Breakers and Maintenance
    If you have a tie breaker between two main breakers (A and B), on which breaker do you perform maintenance first? Answer: Do maintenance on the tie breaker first.

    There are several reasons for this. In a typical application, the tie breaker is open, and you can’t close it unless you have first closed breaker A or B. So, the tie breaker isn’t subject to stress because it isn’t carrying any load. You already know breakers A and B can carry the load because they are doing that now. You don’t know that the tie breaker can carry the load, because it’s not doing so now and you don’t have any test data to prove it can. Thus, you test the tie breaker first.

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    Electrical Troubleshooting Quiz
    Your facility has a large, multifunction machine. It’s fed by a roll of steel, and it produces stamped and welded panels. Operators are complaining that:
    • They get headaches and eyestrain (although the lights don’t appear to be dim).
    • The stampings lack the proper definition, even though the dies meet spec and the settings are correct.
    • The welds don’t look uniform and don’t look right.
    Can there possibly be a root cause common to these problems? If so, how can you determine what it is?

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

    Motor Repair, Part 2
    In Part 1, we said you need to be a bit of a forensic examiner to do a proper motor repair. You should also tap the expertise of another forensic examiner: your motor repair shop.

    A repair isn’t complete just because you’re running again. A repair is complete only when you’ve fixed the cause of the failure. You can’t fix what you don’t know.

    Send a failed motor to the motor shop for postmortem analysis, if the cause is unknown and any of the following apply:

    • The application is critical.
    • The application makes replacement difficult, dangerous, or time-consuming.
    • The motor is large (and, thus, expensive).
    • A motor failed prematurely (regardless of cost or criticality).
    Important: Identification of a root cause issue with a noncritical motor can help you prevent failure of a critical one.

    Fuses and Capacitors
    You may have a capacitor bank for any number of reasons. For example, you may have one at your service entrance for power factor correction. Or, you may have one because you need to draw high current briefly for process reasons. Capacitors can solve a large number of problems, but they can also add problems if you don’t fuse them correctly. This is one reason there are fuses made specifically for capacitor protection.

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    NEC in the Facility
    Dry-type transformers don’t necessarily stay dry. They are called dry-type because they aren’t intentionally filled with a liquid (e.g., oil). They are vented, and water can get in the vents, soaking the paper inside them. When that happens, the safety and performance of the transformer are severely compromised. This is why the NEC requires all dry-type transformers installed outdoors to be in a weatherproof enclosure [450.22]. See Art. 100 for the definition of weatherproof.

    Why You Should Report Any Injury, Part 2
    By reporting your injury, you identify hazards that could hurt others. This is true even of a very small injury. For example, someone runs a portable cord across a stairway. You trip, but catch yourself. Your only injury is a minor scrape on your elbow, so you just reroute the cord problem and don’t report the injury.

    The next day, the same person drapes the same cord across the same stairway. A coworker trips over it and breaks his arm. Had you reported your injury (and the unsafe act), steps could have been taken to prevent your coworker’s injury.

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    Quiz Answer
    Answer to Electrical Troubleshooting Quiz
    The root cause appears to be a power problem. Low-level lighting flicker could cause the eyestrain, which would cause the headaches. Power distortion or low voltage could cause the tooling problems and the flicker. Use a power analyzer to identify power anomalies.

    First steps in solving any “mysterious” power anomalies on this machine:

    1. Have the machine’s capacitors properly tested.
    2. Inspect every connector and raceway on the machine for “grounding” (bonding) path continuity.
    3. Inspect all related equipment for bonding deficiencies (per NEC Art. 250 Part V and IEEE-142).

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