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CONTENTS
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Pay Attention to the Details
Electrical Troubleshooting
Quiz
Infrared and Repairs
NEC in the Facility
Safety Rules
Mitigating Harmonics in Commercial
Environments
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
National Electrical Code®, which is a registered
trademark of the National Fire Protection Association.
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Maintenance
Pay Attention to the
Details
You've probably heard the saying, "The devil is in the
details." This expression means that proper execution at the detail
level makes all the difference in how well a project turns out. For
example, a wiring job is good only when wiring is properly dressed and
labeled.
In the maintenance world, even a minor detail can mean the
difference
between high uptime and a lengthy loss of service. Examine 100
failures,
and you'll probably find that 80 occurred because a detail or two
wasn't
right.
Don't take this too far, however. Focusing on details without regard
to the larger picture will bedevil your maintenance efforts. Experts on
subjects ranging from time management to family relationships say to
start with deciding on your mission, goal, or desired result. In his
book, "The Seven Habits of Highly Successful People," Stephen R. Covey
writes, "Begin with the end in mind." This philosophy also applies to
maintenance.
Unfortunately, managers at the corporate, division, and plant level
often
seem oblivious to this idea. Rather than understand and support the
maintenance mission, some of them try to score short-term points by
"saving money" -- usually at great cost.
An example of this occurred in a plant that made parts for HVAC
systems. The plant controller decided to reduce expenditures by
limiting
the maintenance credit card to $100/month. He didn't understand that
the
card was used by a second-shift hourly person to buy chemicals for
treating the chilled water and to buy oil for the presses.
When that employee was unable to use the card to buy the $120 worth
of chilled water chemicals needed for that month, he felt frustrated
and
angry at management. So, he gave up and didn't make the necessary
purchases. The untreated water was soon filled with algae, and things
started shutting down. Sure, that controller saved $20. But the total
cost of repair was more than $15,000. Downtime costs were considerably
more. In our next issue, we'll look at how to get everyone on the same
page.
ADVERTISEMENT
Sign Up Today for InfraMation and Save
Register by July 31st for InfraMation, the world's largest infrared
camera applications conference, and receive 3 free hotel nights and a
free guest pass. Hosted by FLIR, InfraMation will happen on October
15-19, 2007 in Las Vegas. InfraMation features clinics on electrical
applications as well as sessions on condition monitoring and predictive
and preventive maintenance. Visit www.inframation.org, or call
1-800-254-0632.
Repair
Electrical
Troubleshooting Quiz
The overloads for a 75-hp conveyor motor trip several
times per week. You've confirmed that the nominal voltage is correct.
You've confirmed that the overloads are tripping on high current.
You've
performed insulation resistance tests on the motor, and see no
problems.
While the motor was running, you checked bearing temperatures and
conducted vibration analysis -- no problems. What is the most likely
cause, and how do you check for it?
The answer to this question appears at the end of this
newsletter.
Infrared and Repairs
Most of us are aware of how valuable infrared testing
is
for predictive maintenance. One use can easily justify the purchase of
the test equipment. But why not gain even more ROI from that purchase?
You can use IR for more effective repairs.
Consider the following example. A 75-hp motor tripped its overloads
three times in two days. The standard approach in most plants is to
replace the motor and send it out for repair. This approach is quick,
because no troubleshooting is involved. However, it violates a
fundamental rule: Always take "as found" measurements before changing
something.
Using an IR gun, methodically take the temperatures of the motor and
surrounding equipment (work from input to output). You may find a
problem that a motor replacement won't solve or that doesn't require a
motor replacement to solve. A good fix is always better than a quick
fix.
Operation
NEC in the
Facility
In some facilities, a bare copper cable runs from a
panel to a ground rod driven near the panel. This supposedly complies
with 408.40, which says panelboard cabinets and frames shall be
grounded. But the installation does not comply with 408.40.
This is another case in which the NEC uses "grounding" to mean
"bonding." To understand what 408.40 means, read it in its entirety.
It's talking about tying metallic objects together and connecting them
to the equipment grounding (bonding) conductor.
A review of Article 250, Part V, will help clarify 408.40. Two other
good resources are IEEE-142 (Green Book) and IAEI (International
Association of Electrical Inspectors) Soares Book on Grounding.
Safety Rules
This week, make a concerted effort to practice these
two
rules of safety:
- Reread safety information. Out of sight, out of mind. Don't
let this happen with your safety information. It's easy to fall into a
rut of "I've done this before, so I know what I'm doing," but that's
how
people get hurt. Review small bits of your safety information
frequently
(for example, every Tuesday and Thursday, read your safety handbook for
10 minutes).
- Communicate problems clearly. Too often, people lodge a
safety complaint in a manner that makes followup unlikely. Remember
that
your goal is to get the problem fixed. Focus on that. Be specific, and
ask for a specific outcome. Ask when it will be done.
Show & Events
Mitigating Harmonics
in Commercial Environments
This free live conference will be presented by John
DeDad, EC&M magazine, on August 16th at 10 a.m. Eastern and
Pacific times, in the EC&M e-Tradeshow. To gain access to the
event, go to www.ecmweb.com/etradeshow,
sign in or register as an attendee, and follow the signs to the
presentation room. And be sure to take a look at the On-Demand Theater,
where you can view past online conferences 24 hours a day, 7 days a
week, and 365 days a year.
Quiz Answer
Answer to
Electrical Troubleshooting Quiz
A conveyor motor nearly always has a gearbox. Conveyors
require torque, and you multiply motor torque with a gearbox. So in
this
example, it should be no surprise to the reader that this motor has a
gearbox.
You can use an IR gun to quickly check the gearbox temperature while
the motor is running. It should not be much above ambient. Here are
four
other gearbox tests:
- Listen. You might hear a whirring sound, but you should not
hear a whining sound. Knowing the correct sound takes experience, so
ask
an old hand if you don't know.
- Feel. The vibration should feel "smooth" and minimal.
Knowing
the right feel also takes experience.
- Look inside. This is the easiest thing to do. If the line
shuts down for shift changes or maintenance, you can check the oil
level
in the gearboxes on that line. In fact, someone should do this
routinely.
- Smell the oil. A sulfur smell is normal; a burnt smell is
not.
Note that if you have gearbox lubrication and/or wear problems,
replacing the motor won't accomplish anything. Any time you do replace
the motor, check the gearbox. That's also a good time for a gearbox oil
change, even if the box checks OK.
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