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CONTENTS
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Cast Your Vote for the
EC&M Product of the Year!
Insulation Resistance
Testing, Part 4
Electrical Troubleshooting
Quiz
Climbing the Corporate Repair
Ladder
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 4
In our previous issue, we described time-resistance and
dielectric absorption ratio tests. Two other useful insulation
resistance tests are the short time and step voltage tests.
- Short time. This is also called a “spot reading” test.
It's a quick check that reveals gross defects in the insulation. Apply
the test voltage for a designated interval, and then record the
results.
That interval is usually 60 sec. Though you can use any interval you
wish, make your choice only once. Use the same interval consistently,
so
spot readings make sense when compared to "typical" readings.
- Step voltage. Another name for this test is “tip-up.”
It's essentially a spot reading done at one voltage and a second SR
done
at a higher voltage. Good insulation exhibits the same resistance
reading at either voltage. If the readings differ, then there’s a
problem with the insulation (e.g., pinholes, contamination).
Always perform one of these tests before incurring the time and expense
of installing a motor.
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Repair
Electrical
Troubleshooting Quiz
Every so often, your plant seems to lose motor drives
in
batches. Three weeks ago, four drives failed within a few hours of each
other. Last summer, a similar incident happened on two different
occasions with three drives the first time and two the second.
You contacted the drive manufacturer, who asked you to send in two
of
the failed drives. You just got the report back, stating that the surge
protective devices (SPDs) in both drives were fried.
What could be causing this, and what should you do?
Visit EC&M's
Web site to see the answer.
Climbing the
Corporate Repair Ladder
In many industrial systems, the repair process involves
using ladder diagrams for troubleshooting. Unfortunately, these
drawings
frustrate many people in the field. However, if you understand a few
fundamentals, then ladder drawings make sense and become easy to use.
To read more on this story, visit EC&M's Web
site.
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Operation
NEC in the
Facility
Don't confuse surge arresters (Art. 280) with
surge-protective devices (Art.e 285). The main distinction the NEC
makes
is the voltage level: If it's more than 1kV, it's a surge arrester.
Otherwise, it's a surge-protective device (SPD).
This isn't an arbitrary distinction. A single device can't handle
all
voltage levels, due to those pesky laws of physics. Article 280 devices
reduce voltages to levels that Art. 285 devices can handle.
Use Article 280 devices where the higher voltage levels are
encountered (e.g., on the service drop). These devices reduce large
transient voltages, typically by diverting the “peak” of the
transient to ground. An example is the spark gap device. The desired
power does not pass through this device, but the undesired power does.
In a piping system, the equivalent would be a pressure relief valve.
Use Art. 285 devices where the lower voltage levels are
encountered (e.g., on a distribution panel). These devices reduce
smaller transient voltages by blocking or diverting the
“peak” of the transient. Generally, the desired power does
pass through these devices — they are in line with the flow of power.
In a piping system, the equivalent would be a pressure control
valve.
Safety
Think of how many intricate things you do with your
hands just to wire a switch. How well do you protect your hands?
Gloves are the standard PPE for hand protection. However, you must
use the specific type of gloves that fits the situation. For
example:
- For electrical protection, wear gloves suitable to the energy
levels
involved. Test prior to use with the correct method (don't blow into
them).
- If you're using solvents, adhesives, or other chemicals, check the
container label or Material Safety Data Sheet (MSDS) to find out which
gloves to use.
- Wear work gloves in situations where mechanical injury is possible.
A slip with a saw can be a nonevent, or it can send you to the
emergency
room.
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