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CONTENTS
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Maintaining the Motor Environment,
Part
Three
Electrical Troubleshooting Quiz
Upgrading Motors
NEC at the Facility
The Practical Implications of OSHA 1926.417
Answer to Electrical Troubleshooting Quiz
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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
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Maintenance
Maintaining the Motor Environment,
Part Three
Why do motors run? To drive loads. If you haven't
looked
closely at the load, you've overlooked a significant cause of
inefficiency and premature motor failure. Motor maintenance doesn't
stop
at the output shaft. At a minimum, examine these areas:
- NEMA design/load type match. Check your motor data to see if
the motor is a NEMA Design B, C, or D. Then, determine your load's
requirements for starting torque, locked rotor current, and breakdown
torque. A mismatch here is costly. It won't hurt to consult your
distributor or manufacturer for assistance.
- Alignment. Ensure the motor output shaft and load input
shaft
are properly aligned in three dimensions. Laser alignment and vibration
analysis are the standard tools for this. If the alignment is fine but
you have vibration, inspect the couplings.
- Gearbox lubrication. Electronic drives control motor
speed. But it's common to use a gearbox on the output side to
multiply torque. To the motor, this gearbox is the load.
Check the gear lubricant on a periodic basis. Also, determine if you
are
using the best lubricant for the application. In one factory, changing
from regular gear oil to synthetic dropped the temperature of each
gearbox by about 40°F.
- Miscellaneous load issues. In your motor maintenance
procedures, add the task of visually inspecting the load. Ask for
load-specific measurements. Those might include coolant temperature,
running speed, output pressure, and so on. The idea is to record and
trend values so you can quickly spot deviations. If the instruction is
simply "Conduct visual inspection of the load," you won't get useful
information. If the data collection is redundant with other efforts,
consider that there is little cost to taking a few more data points
during motor maintenance and doing so may show you impending failures
at
their earliest, most preventable stages.
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Repair
Electrical Troubleshooting
Quiz
Those process exhaust fans seem to fail on a regular
basis in the summer -- when they are needed most. What are some key
trouble points?
The answer to this question appears at the end of this
newsletter.
Upgrading Motors
Sometimes, you find that the original motor wasn't
appropriate for the application. So, you upgrade. To many people, this
means replacing the motor with one of the next higher horsepower
models.
But that can lead to even more problems.
For example, perhaps the old motor pedestal isn't strong enough for
that larger motor. So after the replacement, you get deflection and
vibration.
Many times, the answer isn't "a bigger motor." The answer could be a
motor with better insulation for thermal characteristics -- or one
matched to that particular motor drive. Before you upgrade a failed
motor:
- Determine the cause of failure. A motor shop can do a post-mortem
to
help you determine this.
- Perform a thorough analysis of the application to determine the
motor requirements.
- Present findings from both efforts to your electrical distributor
or
motor manufacturer for a recommendation.
Yes, you incur additional cost with the motor shop work, and you'll
have
to spend extra time doing the research. This extra cost and effort may
tempt you to just guess "next size up." Anybody can make guesses. To do
the job right, get the facts before you make the purchase.
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Operation
NEC at the Facility
Ensuring Chapter 3 conformance is a fundamental part of
solving many electrical problems. The primary focus of Chapter 3 is the
correct sizing and installation of conductors, raceways, and
enclosures.
A common Chapter 3 error is the use of the wrong ampacity table. To
prevent this error, carefully read the short description at the top of
each Table.
Chapter 3 is easier to understand when you group the Articles into
these categories:
- Wiring methods (300)
- Conductors (310)
- Enclosures (312 and 314)
- Cables (320 -- 376)
- Raceways (378 -- 392)
The Practical Implications of OSHA
1926.417
The subject of lockout/tagout is a source of confusion
for many people. Suppose you place a lock, but no tag, on a breaker.
Then, you finish the work and forget about the lock. On the next shift,
someone -- after asking around and not finding out who put the lock
there -- cuts off your lock. No harm done, other than the cost of
your
lock. But this is a very dangerous game to play.
OSHA requires you to apply both a lock and a tag. One without
the other might protect you. But why gamble?
To work safely:
- Walk down the entire path of energy for the circuit you are working
on.
- Move controls to the de-activated position, and tag them.
- De-energize equipment, then lock it out so it cannot be
energized.
Affix your tag showing what is locked out and who locked it out.
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Quiz Answers
Answer to Electrical
Troubleshooting
Quiz
This quiz ties together several concepts. Here are some
places to start checking for the cause of those failures:
- Exhaust fans normally require NEMA Design B motors, but if your
process exhaust fans have to blow through filter bags, you might need
NEMA Design C motors due to high inertial starts. Ask your filter
system
rep. for a review of your system specifications.
- The filter bags might be under-maintained. If you don't have
differential pressure instruments across those bags to alert you when
the bags need changing, your motors may have a much heavier load than
necessary. In the summer, the air is also more likely to contain
particulates, causing you to use up filter capacity faster.
- In the summer, with its higher ambient temperatures, the motor
might
not have insulation sufficient for the temperatures in which it's
operating. Use a thermal gun to take temperature readings at and near
the motor, during peak heat times. Consider upgrading to a motor with a
higher temperature rating.
- If the fans are belt-driven, check the belt tension and
alignment.
- Summer and winter lubricants are different. If the motors are
subject to summer and winter temperature changes, the lubricant may be
too thin in the summer -- allowing metal on metal contact. Too thick
a
lubricant also causes problems.
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