Maintaining for Energy
Savings, Part 7
Bottleneck Motor Repairs, Part
NEC in the Facility
Answer to Electrical
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MRO Insider addresses topics such
Working with management and supervision
National Electrical Code® on the production floor
Safety procedures and programs
Equipment maintenance and testing tips
Managing motors and generators
Trends in training and education
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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.
Energy Savings, Part 7
If your motors are properly mounted and correctly
aligned, you’ve eliminated a major cause of motor energy waste (and a
contributor to premature failure). If you have a well-planned and
well-managed motor maintenance lubrication program, then you’ve
eliminated a common cause of motor failure and energy waste.
Where else can your motor maintenance efforts save energy? Let’s
start with grounding. Are your motors grounded? If you answered yes,
then you have a problem. Your motors should be bonded, not
grounded (see Art. 100 definitions and Art. 250 Part V).
Let’s examine three related areas for motor energy savings:
How are these three areas related? Proper bonding eliminates many power
quality problems. Good power quality maintenance practices result in
less waste heat being generated in the motor, whether from harmonics,
voltage imbalance, or some other cause. The more you do to eliminate
heat-causing power quality problems, the less work the cooling system
has to do.
- Bonding. Are your motors adequately bonded? Over
bonding jumpers corrode, connections come loose or fail, and parts get
broken. Your PM system should include a PM for visual inspection of the
bonding system for each motor, at least annually. This would be in
addition to the entirely separate maintenance tasks related to
electrically testing the entire bonding system.
- Power quality. Although harmonics and power factor are
important aspects of power quality for motor energy savings, the most
important aspect may be voltage imbalance. A 3.5% voltage imbalance
brings about a 25% rise in temperature, which means waste heat. This
additional heat also promotes premature motor failure. A good power
monitoring system can let you know when it’s time to fix a power
quality problem, so you can keep motors running efficiently.
- Cooling. Establish a program to keep motor filters clean.
may need to replace existing filter setups to make this feasible. For
example, replace screen mesh canisters with something easier to
maintain. Contact a filter supplier for ideas.
Maintain the cooling system so that your other energy-savings
aren’t wasted and vice-versa. You may need to go beyond maintenance
and make some design changes, if the motor runs hot despite having a
clean filter or being a Totally Enclosed Fan Cooled (TEFC).
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The drive motor for a key production line trips its
thermal overloads at least once a week. However, it didn’t start
this until winter, and the trips always happen on second shift. The
maintenance techs take voltage readings and perform insulation
resistance tests but never find any problems. Nor do they encounter any
problems with the restart. Something’s wrong, but what? How can you
isolate and solve this problem?
The answer to this question appears at the end of this
Repairs, Part 3
Previously, we discussed how to identify bottleneck
motors. These should get the highest priority for repair and should
receive the highest priority for implementing measures that reduce
Using your bottleneck motor repair history and the manufacturers’
literature, determine the most likely repairs and the most
time-consuming repairs. Then, make a list of the top three of each. A
longer list is counterproductive.
If you correctly anticipate the key things that can go wrong, then
you can make effective plans to handle them. In our next issue, we’ll
discuss the planning part.
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NEC in the
Class II locations are those that have (or may have)
combustible dust in quantities sufficient to produce explosion or
ignition 500.5(C). Class II (and I and III) locations may be Division 1
(normal operations) or Division 2 (abnormal operations).
- Use Division 1 wiring methods when combustibles are present under
normal operations [502.10(A)].
- Use Division 2 wiring methods when combustibles are present under
abnormal operations [502.10(B)].
Seal requirements for Class II locations [502.15] are simple, unlike
the highly detailed requirements for Class I locations [501.15]. To
avoid confusing Class requirements, remember that as the Class number
rises, the particles become larger (I is for gases, II is for dust, III
is for fibers) and thus easier to contain.
Grounding and bonding requirements for Class II locations are in
502.30. Grounding doesn’t create an equipotential plane, but bonding
does. See the Art. 100 definitions.
"Misconduct" generally means willfully doing something
you "should" know is wrong. The "should" part can be a gray area, but
that doesn’t mean the penalties imposed are weak. Misconduct can
result in a "sentence" not handed down by any civilized court, such as
being horribly burned by an arc blast.
Misconduct is a charge that can result in serious consequences even if
you didn’t violate a specific rule. You can be fired, sued, and
prosecuted for it. The "reasonable man theory" is a concept in our
system that says everyone must meet reasonably expectable standards of
behavior, even if no written rule covers a particular action.
Because you can’t appeal to the laws of physics, always ask, "What
must I do to be safe in this situation?"
Electrical Troubleshooting Quiz
Look at power quality monitor logs to see if there’s
some power event associated with the motor trips. For example:
Inspect the area around the motor for what has changed. For example,
maybe operators moved supplies from an area that was too cold for them
to an area that’s warmer but blocks airflow to the motor.
- Perhaps there’s cleanup work that involves running the big trash
compactor at the end of first shift, thus causing waveform distortion.
This could work the motor harder — possibly enough to overheat it.
- At shift change, many people enter and exit the plant. Perhaps this
brings in enough cold air that the plant’s electric heaters stay on
too long and drag down the distribution voltage sufficiently to cause
the motor to overheat.
Perhaps the fact it’s winter is coincidental. Consider the
production line itself — has the process or product changed such that
the motor now has a heavier load? If the motor drives a gearbox, maybe
there is not enough lubricant or the lubricant needs changing.
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