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August 19, 2008 A Penton Media Publication Vol. IV No. 16


CONTENTS
Do You Have a Calibration Plan?

Motor Maintenance Tip, Part 19

Electrical Troubleshooting Quiz

Reassembly During Repair

Fuses for Motor Controls

NEC in the Facility

Safety

Answer to Electrical Troubleshooting Quiz


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MRO Insider addresses topics such as:

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    Maintenance
    Do You Have a Calibration Plan?
    Although today’s test equipment is highly reliable, it can go out of calibration over time. Depending on the use of the test equipment, this could be a problem.

    For example, if you use a DMM to verify 480V transformer connections, a deviation of 0.01V isn’t going to matter. But if you’re checking the sensors for a process control system, this could mean the difference between good product and scrap.

    If you don’t have a test equipment calibration plan in place, assess the maintained equipment to see if one is necessary. If you have tight tolerances, safety related systems, or critical trending (e.g., insulation resistance on critical cables), it probably is.

    If you have only a few instances of “calibration advised” in your facility, you could cut costs by assigning specific test equipment to those specific instances and then following the recommended calibration frequency on just those items. Adding that test equipment to your CMMS will prevent “forgetting” when the calibration is due.

    Another option is to outsource the tests that require calibrated test equipment. If you do that, ensure the testing firm provides calibration records of the test equipment being used. Come to an agreement of how to handle retesting in the event that test equipment is found out of calibration after your tests are completed.


    Motor Maintenance Tip, Part 19
    You can have a motor-killing voltage imbalance at the panelboard or at the motor control center (MCC), due to loose or poor connections. A feeder wire joint that is dirty, loose, or corroded will have resistance the other wire joints don’t have. The voltage drop across this bad wire joint subtracts from the system phase voltage and results in voltage imbalance at the load.

    Don’t overlook voltage imbalance at the motor. The same loose joint problem can hit here, not just at the MCC. At the motor, you have more to look for. Consider the contacts within the circuit breaker, motor starter, or drive. Look at lugs and T-leads.

    In any of these cases, make your phase-to-phase voltage measurements with the motor running. Begin at the easily accessible motor controller load-side lugs and proceed either upstream or downstream. Go upstream if you find voltage imbalance and downstream if you don’t. Where you find the voltage imbalance first appearing (farthest from the transformer) is where you’ll find your bad conductor joint.


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    Repair
    Electrical Troubleshooting Quiz
    A commercial office building with 4-foot fluorescent fixtures has had a group relamping program in place for several years. So, until recently, there was no need for spot relamping. Over the past few months, however, you’ve had repeated lamp failures — even in areas that were relamped less than six months ago.

    What could be causing this, and where do you start troubleshooting?

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


    Reassembly During Repair
    After a tense period of downtime, the repair crew puts the equipment back in service. Then someone asks, “What about these leftover parts?” You look, and there you see a missing bracket, a couple of washers, a spring, and some other mysterious parts that didn’t make it back into the equipment.

    Somehow, telling people to be more careful doesn’t solve the problem of incorrect reassembly. Nor does laying out the parts exactly as they came out (assuming you can do that), if somebody accidentally kicks the parts. The solution that works is the same solution used to assemble things in the first place: Use a drawing.

    The equipment service manual should have exploded view drawings and/or assembly instructions. But what should you do if it doesn’t? You could create your own drawing on the fly, during an equipment breakdown. However, a better solution is to go through your equipment documentation and contact manufacturers for what’s missing. Then, you’ll have it when you need it — and no more leftover parts.


    Fuses for Motor Controls
    To avoid confusion when sizing fuses for motor control circuits, refer to Table 430.72(B). This provides the maximum ratings, depending on which of three conditions apply.


    Operation
    NEC in the Facility
    For any indoor dry-type transformer of 112.5kVA or less, ensure there aren’t any combustible materials within 12 inches of it in any direction [450.21(A)]. The only way “around” this rule is if there is a fire-resistant, heat-resistant barrier between the transformer and the combustible material.

    Compliance with this rule is a constant battle in many facilities, as people try to use electrical equipment rooms as storage rooms for file boxes and fluorescent lamps. If you have this battle, make it clear to management that the insurer requires NEC compliance, and failure to comply may void coverage as well as incur operational losses.


    Safety
    Safety isn’t the personal decision many people think it is. One person’s unsafe act endangers others. Suppose you tape up a portable cord instead of removing it from service. Then, a coworker who isn’t even using that cord touches a surface energized by it and dies from electrocution. Or, suppose you leave wire scraps on the floor. A coworker slips, falls, and is permanently disabled.

    Any unsafe act can have a devastating effect on a coworker. Don’t be the unsafe person performing unsafe acts. The flipside also applies: Don’t let a coworker be that hazardous person. Report dangerous acts to your supervisor.


    Quiz Answer
    Answer to Electrical Troubleshooting Quiz
    This situation involves widespread failures, indicating a common cause such as a transient voltage. The problem is unlikely to have been caused by a single event such as a lightning-induced transient. You probably have an ongoing transient source, such as equipment recently put into service.

    But maybe existing equipment or cabling has deteriorated and become a source of damaging transients. That includes equipment at a neighboring facility.

    It might not be a transient voltage, after all. You may have bonding deficiencies, due to deterioration or human error. Or, you could have any of several types of power anomalies.

    How can you find the needle in this proverbial haystack? It’s simple: Use a power monitor. Because commercial offices typically don’t have power monitoring systems in place (but the day will come), use a good power analyzer or portable power monitor.


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