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April 20, 2010 A Penton Media Publication Vol. VI No. 8



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

Insulation Resistance Testing, Part 5

The Ins and Outs of Ladder Diagrams

Electrical Troubleshooting Quiz

NEC in the Facility

Protect Your Control System from Potential Cyberattacks


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This twice-a-month
e-newsletter is brought to you from the publisher of EC&M magazine.

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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    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
    Insulation Resistance Testing, Part 5
    Sometimes, an insulation resistance (IR) testing program is in place, yet a major cable failure still occurs. Because it doesn't seem to work, cutting back or eliminating the program appears to make sense — that is, until you look deeper.

    In these situations, what hasn't happened is consistent testing followed by consistent trending. What makes an IR program work is the ability to trend data over time. A proper trend can't exist unless you do the same tests the same way on the same schedule every time. The only variation in the testing should be temperature adjustment, which also must be done in a consistent manner.

    Figure out ahead of time what the testing interval will be for a given type of equipment, and stick to that interval. If you don't, then the program will fail as will your equipment. To determine that interval, you must balance a realistic level of access (and required downtime) against the minimum testing frequency that will allow you to detect insulation deterioration in a timely manner.


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    Repair
    The Ins and Outs of Ladder Diagrams
    In a PLC-controlled system, problems rarely occur inside the PLC. A malfunction is nearly always on the input side or output side of the PLC. The ladder diagram shows you what the inputs and outputs are, and it shows how each output responds to a given input change. This is, in fact, what makes a ladder diagram especially useful for troubleshooting — you can follow the current flows of control circuits to find what's wrong.

    The output of one control circuit is often the input to another elsewhere on the drawing. For example, at line 27 on your drawing, a limit switch is an input to a relay control circuit. The circuit ends with a coil contact (output). When tripped, the switch provides a signal and the coil picks up, thereby energizing the contact.

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


    Electrical Troubleshooting Quiz
    Let's use that mixer example from above. Suppose you can see that the limit switch is tripped, but there's no power coming out of the motor starter. Can you outline the next few troubleshooting steps?

    Visit EC&M's Web site to see the answer.


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    Operation
    NEC in the Facility
    The typical maintenance department has several spools of THHN wire on a rack or pallet, ready for projects or repairs. THHN is a good, general-purpose insulation. However, suppose you need to rewire a machine tool. Would THHN be the most appropriate kind of wire? Would it be appropriate at all?

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


    Protect Your Control System from Potential Cyber Attacks
    Like most facilities, yours probably has established maintenance, availability, and safety programs in place. But is there a program that guards your control system against possible cyber attacks?

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



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