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June 24, 2008 A Penton Media Publication Vol. IV No. 12

The Power of Information -- Take 4

Motor Maintenance Tip, Part 15

Electrical Troubleshooting Quiz

Special Resources

OCPDs and Short-Circuit Current Ratings

NEC in the Facility


Answer to Electrical Troubleshooting Quiz

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MRO Insider addresses topics such as:

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    The Power of Information -- Take 4
    Three types of information can take maintenance to the next level of performance:
    1. Replacement parts information. Hunting around for spare parts is inefficient. Installing the wrong part can cause massive failure. For critical spare parts, identify part numbers, acceptable substitutes, sources, and lead times.
    2. Software documentation. Today, software documentation is seldom in print form. Typically, you access it via the Help menu, which may be online or resident in the software. Producing a paper archive of this documentation can create an “information silo” that does more harm than good. Instead of printouts, keep a record in your system of the following: default settings, your settings, revision history (with dates and exactly what was changed), license codes or keys, and vendor support information (URL and e-mail).
    3. Supplemental information. This includes technical bulletins, upgrade information, user group information, and training materials. Many training materials today are online and in video form.

    Motor Maintenance Tip, Part 15
    Excess vibration destroys motor bearings, windings, and even cases. Vibration causes are usually mechanical: excessive belt tension, defective ball or sleeve bearings, misalignment, imbalance, a weak motor base, or a weak motor pad.

    The most common cause of vibration is an unbalanced rotating part, such as the rotor, a drive train component, or the rotating load. The motor rotor is the least likely culprit. If you uncouple the motor from the load and run it, you usually find the vibration is gone. This means you have isolated the problem to the load.

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    Electrical Troubleshooting Quiz
    After a system crash and restore, the control system for Line 3 isn’t working. The operators can see their controls, but they can’t get the system to respond to control commands. Is it time to make a panic call to the equipment vendor, or is there something you can do to restore operation?

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

    Special Resources
    Repair on some equipment requires special tools, fixtures, or test equipment. Make sure these special items are there and serviceable before the need for them arises.

    One technique for making this happen is to create equipment-specific repair kits, and keep them at the equipment or in a cabinet nearby. This way, you never spend precious downtime walking around looking for things. If these kits contain any consumables (e.g., special greases), put them on a PM schedule so they’re ready when you need them.

    OCPDs and Short-Circuit Current Ratings
    The NEC requires overcurrent protection devices (OCPDs) to clear a fault without extensive damage to the electrical components of the circuit [110.10]. The short-circuit current rating of each component in the circuit is one of the factors 110.10 requires you to consider when selecting OCPDs.

    NEC in the Facility
    Most facilities contract out the installation, repair, and maintenance of chillers and HVAC systems. This makes sense for many reasons, including licensing requirements pertaining to the coolant.

    However, it has a downside. The techs of the typical HVAC firm are mechanical, not electrical. Violations of Art. 440 (and several other Code requirements) naturally result from such a situation. Violations typically get caught after job completion, when resolution costs more than doing the job right the first time.

    The obvious solution is to review plans and drawings prior to commencement of the work. Review the work in progress to ensure those plans and drawings are being followed. The most common errors include:

    • Design stage: Circuit protection.
    • Installation stage: Location of disconnects.
    Misapplication of raceways is another common error, occurring in both stages.

    Work neatly. To many people, this idea belongs in the category of good workmanship, not safety. Yes, working neatly is a proven way to do work that looks good. But it’s also a proven way to prevent lethal errors.

    Good housekeeping doesn’t mean cleaning up after the job is done. It means making neatness part of how you do your work. A messy workplace is a dangerous workplace. Think about the number of tripping hazards presented by a few scattered tools or boxes. Keep work areas free of debris, scrap, and loose parts.

    But this goes well beyond tripping hazards. As you work, make sure you aren’t leaving yourself exposed to the additional hazards of fire, slipping, and cutting. Examples:

    • Fire. Small spills of solvent. Clean these up immediately.
    • Slipping. Small spills of cable lube. Clean these up before you start the next pull.
    • Cutting. So, you’ve made a nice hole in a cabinet for that control switch. Remove any burrs from that hole and clean up the metal shavings.

    Quiz Answer
    Answer to Electrical Troubleshooting Quiz
    Today, a system may consist of several subsystems provided by multiple vendors, each with their own software licenses. These systems tend to be modular, and each module (subsystem) must work for the system to work. For example, a production control system might have a Crystal Reports license for sending managers statistical process control (SPC) reports, along with an interlock that prevents operation if this subsystem isn’t running.

    In the case of a system crash and restore, you may need to reinstall licenses so you can run the full version instead of the demo. You will probably have to replace factory default settings with those you were using prior to the crash. To get the system running, start by resolving any error messages and network access issues.

    If you set up your maintenance system correctly, you should have a listing of the licenses (typically a text string, but possibly a token or XML file) and a record of the required settings for each of the various subsystems. It’s now just a matter of checking to see that every subsystem has its license and the settings are correct. That process is fairly quick and painless.

    But if you don’t have your maintenance system set up correctly, you will have to locate the license keys — possibly by digging through archived e-mails. The next challenge is determining the correct settings. If the necessary settings aren’t on record, you will essentially need to re-engineer the system.

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