Optimize your Predictive
Maintenance (PdM) System, Part 2
Motor Maintenance Tip, Part
Common Repair Mistakes, 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
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The designations "National Electrical Code” and “NEC” refer to the
National Electrical Code®, which is a registered
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Predictive Maintenance (PdM) System, Part 2
With PdM, you are proactive instead of reactive. Not
only is this cheaper and easier, but it also means less downtime --
sometimes a lot less.
In Part 1, we asked how well you implement three key PdM methods:
infrared thermal analysis, ultrasonic surveys, and visual inspection.
Here are three more for you to ponder.
- Oil analysis. This is an easy and accurate way to gauge the
health of your liquid-filled transformers. All you have to do is
an oil sample and send it to a testing lab. Contact the manufacturer of
your transformer if you don't have this testing in place.
- Partial discharge (PD) testing. If you have any
medium-voltage or high-voltage cables or equipment (switchgear, motors,
generators, transformers, etc.), put them on a PD testing schedule.
leakage test is a standard way of identifying insulation degradation
other problems. If you don't have in-house PD testing expertise,
consider outsourcing this to a qualified testing firm.
- Power monitoring. Don't just install a system and think the
job is done. Do you have someone monitoring the power monitor? Do you
know how to interpret the information provided? Are you monitoring the
points that really matter?
Tip, Part 2
Bond against power quality (PQ) problems. It's true
harmonics and other PQ problems can cause serious problems. For
they can damage motor steel laminations, bearings, and insulation.
This is why many maintenance programs now incorporate PQ
measurements, such as waveform analysis and harmonic content readings.
However, if you see harmonics on a PQ analyzer, don't immediately go on
a PQ crusade.
Instead, ensure the installation conforms to Part IV of NEC Article
250 and the connections are in good shape. If your maintenance
doesn't address this, update your procedure. If you maintain the
system, many "typical" PQ problems will never occur on your motors.
FLIR's New ThermaCAM® T400 Infrared Camera Features
FLIR's new, innovative T400 boasts fusion, which allows for easier
identification and interpretation of infrared images. Fusion enhances
the value of an infrared image by allowing you to overlay it directly
over the corresponding visible image. The T400 does this in real-time
and the overlay function can be adjusted suit electrical surveys and
mechanical inspections. Visit www.goinfrared.com/em6, or
A motor keeps dropping offline. It's protected by
thermal devices, which have been replaced several times. Using your
you find a 3% voltage imbalance. How do you find the source of the
The answer to this question appears at the end of this
Mistakes, Part 4
It can be costly not to address voltage imbalance
whenever a motor trips. Typically, what happens is the repair tech
doesn't find any ground faults or direct shorts so he decides it's safe
to energize the motor and see what happens. The restarted motor runs
just fine, the protective device doesn't trip, and all seems well.
This scenario repeats itself on the next shift or maybe days later.
All the while, the motor is running too hot but not quite hot enough to
trigger its protection device. Or maybe it does trigger the device, but
the repair technician "corrects" the problem by tweaking up the
on an adjustable breaker.
At a plastics plant in Kentucky, a technician encountered repeated
thermal overload device trips. His solution was to position a portable
fan in front of them. In addition to the obvious safety problem, this
effectively upsized the protection thereby leaving the motor
unprotected. The actual problem, diagnosed three motors later, turned
out to be voltage imbalance.
Physicians refer to symptoms as being chronic (constant but at a
fairly low level) or acute (sudden and at a high level). Chronic heat
destroys the motor even if never triggers any protective devices. The
resulting premature failure will invariably happen on a holiday
a backshift, or during a critical production run.
NEC in the
The job of sizing motor conductors can be confusing,
it's frequently done wrong. One of the most common mistakes is
incorrectly determining the current rating. To get this right,
the kind of motor you have and work to the applicable requirements as
- Adjustable voltage motors (AC) [430.6(2)(C)].
- Corded motors [400.5].
- Torque motors [430.6(2)(B)].
- General motor applications [430.6(1)].
OSHA devotes many pages to portable and stationary
heaters (gas and electric). The NEC devotes an entire Article (424) to
fixed electric space heaters alone. Why is so much attention given to
equipment everybody knows how to use?
The main reason is people are so accustomed to using this equipment
that they sometimes don't stop to apply the safety rules. Familiarity
Fire due to nearby combustibles is a danger we can easily visualize,
because we can see when combustibles are too close to a heater. But
if you are doing testing or repairs during shutdown and it's really
You fire up that gas heater, but fail to ventilate properly. You
don't see the carbon monoxide, and you can't smell it. As your brain
gets less oxygen, you are less attentive. Your risk for a lethal
incident as a secondary consequence of the ventilation problem
Electrical Troubleshooting Quiz
Voltage imbalance can have more than one cause at the
same time. To find them all, use a methodical approach. Start with the
system one-line, and proceed from the service to the feeder to the
individual load (this motor). At the point where you first encounter a
voltage imbalance, check the transformer. Most likely, the voltage is
balanced on the primary but not the secondary. Look for such things
Note that bonding errors can be anywhere on the distribution but are
most likely to exist on transformers and process equipment assemblies.
Look for driven rods next to these.
- Poor single-phase load distribution on a panel fed by that
- Bonding errors, especially grounding posed as bonding (See Article
250, Part V).
- Transformer integrity issues. Conduct standard transformer
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