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March 23, 2010 A Penton Media Publication Vol. VI No. 6



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

Insulation Resistance Testing, Part 3

Electrical Troubleshooting Quiz

Repairs with Bellevilles

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
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  • 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 3
    Four kinds of insulation resistance tests are particularly useful. Two of these include:

    1. Time resistance. This method consists of trending a series of readings taken at fixed intervals. If you have no insulation resistance history, then this method can help you make a reliable assessment. If the insulation is sound, the trending graph shows an increasing level of resistance.
    2. Dielectric absorption ratio. With this method, you perform two time-resistance (TR) tests and then divide the readings of one by the other to get a ratio. Two common ratios are a 10-min. TR divided by a 1-min. TR, and a 60-sec TR divided by a 30-sec TR. That first ratio gives you the "polarization index" established in IEEE Standard 43-2000 in 1974. That index provides a standardized way of using the data, and is worth learning more about.
    The manual for your insulation resistance tester provides specifics on these tests, as does the manufacturer's Web site. We'll discuss two other tests in our next issue.



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    Repair
    Electrical Troubleshooting Quiz
    An odd discrepancy exists on all of the feeders. Each feeder is busway. On each one, voltage drop (which, by definition, is a calculation) shows one value but actual measurement shows a much higher value. This means energy waste.

    Your boss, eager to have it fixed, scheduled a shutdown for you to conduct insulation resistance tests. In parallel with this, your boss has a crew of mechanics coming in to ensure the connections are good. What should you tell your boss?

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


    Repairs with Bellevilles
    In our previous issue, we ended this section with the question, "For feeder bus 06E, which Belleville washers do we use?"

    The most common bolted connection consists of a bolt, spring-type lockwasher, and nut. This method concentrates the clamping power on one point of the connection hardware. The uneven clamping, normally not a problem, is a problem for current-conducting bus bar.

    The solution is the Belleville washer, which spreads clamping force along a continuous arc for more even pressure at the joint. However, this solution is good only if the washer is used correctly, which it's often not.

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




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    Operation
    NEC in the Facility
    The actual connection of surge arresters can be confusing. You have to read Art. 280, Part II, carefully to get this right.

    In the NEC and other standards, the word "grounding" is often misused to mean "bonding." That isn't the case in Art. 280. It really does mean grounding (per Art. 100, "grounding" is an earth connection).

    Your decision on where you locate surge arresters has to account for your intended wiring scheme, keeping in mind that you want the grounding conductor(s) to be as short as is practical [280.12]. You can locate surge arresters indoors or outdoors, but either way you have to make them inaccessible to unauthorized personnel [280.11] (unless you get surge arresters listed for installation in accessible locations and comply with the installation instructions for those).

    The grounding connection is crucial. Remember: The grounding conductor of a surge protector is not the same thing as an equipment "grounding" (bonding) conductor (EGC). With an EGC, you are eliminating differences of potential. Connecting an EGC to ground doesn't do anything but waste wire. However, with the surge protector, you are actually intending to establish a path to earth. Toward that end, 280.4 provides seven variations of such a path.


    Safety
    With spring comes warmer weather. At most facilities, that means doing "post-winter" preventive maintenance (PM) work. Much of this PM work will involve the use of ladders. For example, inspecting or relamping outdoor security lights, testing entryway sensors, checking roof-mounted HVAC units, and manually adjusting various overhead equipment are all typical "post-winter" activities.

    Ladders may be permanently attached (common for roof access) or portable. If portable, they will likely be extension ladders or stepladders. Each type has its inherent dangers, but some general rules apply to all. For example:

    • Don't carry items up a ladder; use both hands for climbing the ladder.
    • Use a rope and bucket or similar means to raise and lower tools.
    • Only one person on a ladder at a time.


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