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CONTENTS
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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
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About This Newsletter
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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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The designations "National Electrical Code" and "NEC" refer to the
National Electrical Code®, which is a registered
trademark of the National Fire Protection Association.
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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:
- 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.
- 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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