Cast Your Vote for the
EC&M Product of the Year!
Testing, Part 3
Repairs with Bellevilles
NEC in the Facility
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Product of the Year Competition
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
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help us identify the 2010 EC&M Product of the Year Platinum,
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Resistance Testing, Part 3
Four kinds of insulation resistance tests are
particularly useful. Two of these include:
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.
- Time resistance. This method consists of trending a series
readings taken at fixed intervals. If you have no insulation resistance
history, then this method can help you make a reliable assessment. If
insulation is sound, the trending graph shows an increasing level of
- 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
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.
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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.
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,
solution is good only if the washer is used correctly, which it's often
To read more on this story, visit EC&M's Web
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NEC in the
The actual connection of surge arresters can be
confusing. You have to read Art. 280, Part II, carefully to get this
In the NEC and other standards, the word "grounding" is often
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
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
intending to establish a path to earth. Toward that end, 280.4 provides
seven variations of such a path.
With spring comes warmer weather. At most facilities,
that means doing "post-winter" preventive maintenance (PM) work. Much
this PM work will involve the use of ladders. For example, inspecting
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
Each type has its inherent dangers, but some general rules apply to
- Don't carry items up a ladder; use both hands for climbing the
- 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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