Maintaining the Motor Environment,
Electrical Troubleshooting Quiz
NEC at the Facility
The Practical Implications of OSHA 1926.417
Answer to Electrical Troubleshooting Quiz
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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.
Maintaining the Motor Environment,
Why do motors run? To drive loads. If you haven't
closely at the load, you've overlooked a significant cause of
inefficiency and premature motor failure. Motor maintenance doesn't
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
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
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
their earliest, most preventable stages.
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Those process exhaust fans seem to fail on a regular
basis in the summer -- when they are needed most. What are some key
The answer to this question appears at the end of this
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
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
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
Yes, you incur additional cost with the motor shop work, and you'll
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.
- Determine the cause of failure. A motor shop can do a post-mortem
help you determine this.
- Perform a thorough analysis of the application to determine the
- Present findings from both efforts to your electrical distributor
motor manufacturer for a recommendation.
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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
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
Chapter 3 is easier to understand when you group the Articles into
- Wiring methods (300)
- Conductors (310)
- Enclosures (312 and 314)
- Cables (320 -- 376)
- Raceways (378 -- 392)
The Practical Implications of OSHA
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
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:
Affix your tag showing what is locked out and who locked it out.
- Walk down the entire path of energy for the circuit you are working
- Move controls to the de-activated position, and tag them.
- De-energize equipment, then lock it out so it cannot be
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Answer to Electrical
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
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
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
- 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
lubricant also causes problems.
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