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May 18, 2010 A Penton Media Publication Vol. VI No. 10



CONTENTS
Cast Your Vote for the EC&M Product of the Year!

You and IR, Part 2

Electrical Troubleshooting Quiz

Troubleshooting PLC Digital Input Modules, Part 1

NEC in the Facility

Safety


About This Newsletter
This twice-a-month
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MRO Insider addresses topics such as:

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  • 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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    Product of the Year Competition
    Cast Your Vote for the EC&M Product of the Year!
    Would you like to help pick the prestigious EC&M Product of the Year winner and qualify for a chance to win $100? If you're an EC&M subscriber, make your vote count by visiting the 2010 EC&M Product of the Year category winners list. To review the products, click on the links for each of the 33 category winners to read a brief description and view a photo. Once you're finished with your review, visit the polling page, enter your contact information, choose your favorite product from the drop-down menu, and click submit.

    Your selection will help us identify the 2010 EC&M Product of the Year Platinum, Gold, and Silver award winners. As an added incentive, three lucky voters will be randomly selected to receive a $100 gift check.

    The voting poll will remain open through 5 p.m. on June 18, 2010. Please, only one vote per EC&M subscriber. Any votes received from manufacturers, PR firms, or non-EC&M readers will be discarded.


    Maintenance
    You and IR, Part 2
    A fundamental question to ask when analyzing anything is, "Compared to what?" With no point of reference, facts and figures can grossly mislead you. It’s the same with infrared thermography (IR) — you need benchmarks.

    Most thermographic cameras provide for various benchmarks, such as:

    • Ambient. What's the temperature outside that cabinet?
    • Background. What's the temperature inside that cabinet?
    • Reference. What's the temperature of the side panel surface of that cabinet?
    When you later analyze images and spot temperatures, you'll be looking for the deltas between benchmarks and readings. If this is the latest in a series of trended surveys (including perhaps a baseline survey), then you can compare the deltas over time. An area or object with a rise in delta will be easy to spot graphically.



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    Repair
    Electrical Troubleshooting Quiz
    You report in on the night shift to discover that a solvent day tank overflowed three times that afternoon. However, operators say the tank is properly supplying the process.

    The notes from the responding tech include:

    1. Tested level switch by operating rocker. Meter shows voltage change when switch operates.
    2. Simulated open signal to tank fill valve, and it functions properly. Simulation was done by forcing logic in PLC.
    3. Unable to test further, due to time constraints.
    With this information on hand, what should you do next?

    Visit EC&M's website to see the answer.


    Troubleshooting PLC Digital Input Modules, Part 1
    By definition, digital inputs are either on or off. Thus, verifying the absence or presence of voltage is a critical part of troubleshooting digital input modules. But what voltage should you look for? That depends on the power source for the input loop(s) in question.

    The following are some basic facts about input loop power sources:

    • The input module usually isn't a loop power source.
    • Although 120V is common for digital loops, other voltages are also used.
    • There are two types of digital input, differentiated by their power source: isolated and non-isolated.
    • Non-isolated inputs are powered by a common source. For example, the wiring diagram shows a non-isolated input module with L1 (common power source) feeding an array of input devices displayed in ladder fashion.
    • An isolated input is on its own channel and may be powered by its own source. If your system had four such inputs, then the wiring diagram would again show an array of input devices displayed in ladder fashion. But this time, they wouldn’t share L1. Instead, each would be supplied by L1a, L1b, L1c, and L1d.
    To read more on this story, visit EC&M's website.



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    Operation
    NEC in the Facility
    How do you find the ampacity requirements that apply to your facility's power distribution wiring, and which of the many ampacity tables in Art. 310 is the right one?

    To answer the first question, we can quickly cut Art. 310 down to size. About half of it is for 2,001V or more, and everything from 310.60 onward is for 2,001V or more. The parts that typically apply to facilities end at Section 310.15.

    The requirements in 310.1 through 310.14 are general requirements. Then, you have 310.15 and the next section is 310.60 (2,001V and above). This means that, for purposes of calculating ampacity, your requirements are in 310.15 (unless you're working power distribution at greater than 2,000V).

    To read more on this story, visit EC&M's website.


    Safety
    Some ladder safety rules depend on the type of ladder you use.

    Three rules for extension ladders include:

    1. Secure the ladder so it can't inadvertently slide out from under you. One way to do this is to tie a lower rung to an anchor point (e.g., vertical I-beam).
    2. Leave at least three rungs of overlap between sections, or get a longer ladder.
    3. Extend the ladder so it reaches 3 ft above the top supporting point.
    Three rules for step ladders include:
    1. Open it completely, and lock the braces.
    2. Rest all four feet on level footing.
    3. Stand only on steps that are below the top step.


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