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May 6, 2008 A Penton Media Publication Vol. IV No. 9

Cast Your Vote Now!

The Power of Information

Motor Maintenance Tip, Part 12

Fixing "Repair to Fail"

Clear Up Semiconductor "Con-fuse-ion"

NEC in the Facility


Answer to Electrical Troubleshooting Quiz

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MRO Insider addresses topics such as:

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  • National Electrical Code® on the production floor
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  • Troubleshooting techniques
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  • Trends in training and education
  • Managing energy use

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    The Power of Information
    To properly support your maintenance and repair efforts, your maintenance system needs certain information for each piece of equipment. For example:
    • Nameplate data. Here’s a tip overheard at a NETA conference: Photograph the nameplates with a digital camera. This eliminates any chance of a transcription error, and it saves time. Nevertheless, it has its limitations — you may need to capture some of the nameplate data as text, and that means additional steps. This situation may arise, for example, if you’re using motor application or maintenance software that uses nameplate data for calculation purposes.
    • Equipment purpose and use. A summary of what a specific piece of equipment does will help people correctly interpret the drawings and other documentation. The person working on the equipment should understand precisely how it interacts with the system that it is a part of. A lack of such understanding is often mentioned in fatality reports.
    • Location of equipment and controls. Obviously, this prevents the time drain of looking for things. But there’s another important advantage to doing this. Listing the controls and where they are makes it far less likely someone will overlook an energy source and consequently fail to lock it out.
    • Equipment drawings. The electrical ones include wiring diagrams, interconnection diagrams, schematics, power source drawings, and controls drawings. Non-electrical drawings, such as piping and installation, may also apply.
    In our next issue, we’ll look at some other kinds of information that can help you maintain equipment more efficiently and safely.

    Motor Maintenance Tip, Part 12
    If motor maintenance or repair tasks involve stopping and starting a motor, remove as much load as possible. It’s often impractical to mechanically decouple the load, but you may reduce the load in other ways.

    Examples include:

    • Remove product from the conveyor before testing drive motor operation.
    • Remove product from the mixing vat before testing the agitator motor.
    • Start a large air compressor motor in some phase other than the high-demand loading phase.
    • Start a pump without deadheading it. With large pumps, deadheading can destroy the pump.

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    Fixing "Repair to Fail"
    Some equipment seems to be jinxed with breakdowns. It’s just one thing after another. Is there some kind of voodoo going on?

    Most likely, the new failures have resulted from errors made during maintenance or an earlier repair. Consider these examples, and think about how “maintenance errors” might be cropping up in your equipment:

    • Jim fails to clean the zirc before greasing a motor. Two months later, the thrust bearing fails.
    • Mitch steps on a cable, damaging the insulation. The cable fails prematurely and unexpectedly.
    • Bob jogs a motor in reverse before forward motion has stopped. The gearbox starts rattling a few days later.

    Clear Up Semiconductor "Con-fuse-ion"
    A dual element fuse does not give you two shots at overload before it opens. The two elements are in series with each other, not parallel. Dual element construction allows each element to dissipate some of the heat, so it’s typically used to achieve a time delay.

    NEC in the Facility
    Eliminate ground-related starts. It’s a good idea to analyze the control logic on your motor control diagrams. Look at the return paths. Is one side of the motor control circuit grounded (meaning bonded, not an earth connection — see Article 100)? If so, you must ensure that an accidental bonding connection won’t start the motor or bypass manual controls or automatic safety devices [430.74]. For motors on production lines, it’s a good idea to test all of the E-stops to confirm the entire system meets this requirement.

    In many companies, the effort is on safety compliance. This sets the stage for a dangerous game of “not getting caught.” A sure sign of a safety compliance mindset is when people put their safety glasses on as they see their supervisor approaching.

    It’s much better — for each individual personally — to be proactive. Make a conscious effort to protect yourself, other people, and property on/near the job site. Ask, “What could go wrong?” Then, think about what procedures you need to follow to either prevent it from happening or keep you safe if it does.

    Quiz Answer
    Answer to Electrical Troubleshooting Quiz
    This isn’t how an E-stop works. Although it may look like a momentary contact button, it’s not. The way it must work is this: When someone mashes an E-stop, the system shuts down. It can’t restart until someone physically resets that E-stop. If you have any other arrangement, it’s unsafe.

    Because those E-stops aren’t “locking down” this system, you need to test each E-stop to ensure it’s working as intended. If they are 120V E-stops, test them at 120V. Replace any that don’t function correctly.

    Next, look closely at the control logic to see if the E-stops are incorrectly being used as control inputs. An E-stop is not a stop button in the start/stop logic of a motor control system. It’s a physical permissive in series with it. Make absolutely sure there’s no bypass around any E-stop. If so, change that immediately.

    Another question is, “Why is this system restarting on its own?” To answer that, thoroughly review the system logic. The control logic of the motor controller should not allow an automatic restart. The control logic for the system (controller, E-stops, and any other controls) should prevent such a restart.

    Walk through the controller logic to ensure it complies with 430.74. If it doesn’t — and that is probably the case here — then a “ground” (bonding) connection is completing a “line” in the control circuit. The problem isn’t the fact that connection exists. The problem is that the system can start due to that connection.

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