Pareto Chart Basics
Motor Maintenance Tip, Part
Modify to Speed Repairs
Clear Up Current-Limiting
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
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.
Pareto's 80/20 rule means 80% of your results come
from 20% of your efforts. The trick in making this work to your
advantage is determining which 20% to do. A Pareto analysis will tell
you this. A Pareto chart will show you this.
Creating a Pareto chart is easy. For example, suppose you want to
show the top three downtime causes in terms of minutes lost:
This is especially useful if you can do it by "revenue lost" or some
other cost factor, rather than just minutes. Consider limiting your
set to the most critical equipment.
- From your CMMS, generate a report of downtime minutes per cause
the past six months.
- Import the numbers to a spreadsheet.
- Sort the causes by the number of minutes in decreasing order from
left to right.
- Choose a simple bar chart from the selections offered, and let your
spreadsheet create a chart.
- You now have a Pareto chart. The three bars on the left are your
three downtime causes (in terms of minutes).
- Too much information defeats the point of doing this, so use
tags and titles.
Tip, Part 11
Avoid short cycling. The inrush current required to
start a motor is normally about five to six times the running current.
Inrush current means extra heat, but motors dissipate it as they run.
you repeatedly start the motor without sufficient time for heat
dissipation between starts, you overheat the motor. If you aren't sure
how long to wait between starts, contact the manufacturer.
Large motors usually have restart information on their nameplates.
You may find two starting frequencies for the same motor (usually in a
3:1 ratio). If so, use the one that requires the greater time (or fewer
starts per hour). The only time to use the other one (fewer minutes or
more starts per hour) is if you ran the motor continuously since its
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Sometimes, you have to troubleshoot your
not just the equipment. Let's illustrate with an example. Since
obtaining an infrared camera six months ago, you've stepped up your
PdM program. The reduction in downtime has delighted the production
managers. Even the division VP has taken note.
However, opening the various covers takes more labor hours than you
have available, primarily because of the NFPA 70E issues. Cutting back
on the PdM work and then explaining the increase in downtime doesn't
strike you as a particularly brilliant career move. Despite your
success, there's no additional budget for more overtime or more
To compound the problem, people are either dropping cover screws and
not replacing them, or deliberately leaving them out to save time.
One manufacturer told you that replacing the screws with
would cause loss of the testing lab approval, violating NEC
in 90.7, 110.2, and 110.3. You decide that making your plant
is probably not a good idea.
How can you get this highly beneficial PdM work done in less time
while maintaining enclosure integrity?
The answer to this question appears at the end of this
Modify to Speed
A textbook example of production process improvement is
the practice of replacing the screws in a jig (assembly used for
a part) with flip levers. Rather than turn a screw 16 times, you flip a
lever once. This is a huge time-saver.
Some of the access panels you encounter during a repair use screws
hold their covers in place. Replacing these with flip levers can reduce
downtime and possibly improve the integrity of the enclosure. Examine
equipment to see where doing this might make sense.
Note that arc blast and other considerations rule out doing this on
power distribution equipment. In fact, you should inspect covers on
distribution panels for missing screws. If a cover has 18 screw holes,
leaving in only six screws will save time during repair or maintenance.
However, that cover could become a deadly missile during a fault,
instead of serving to protect people and property from the
A semiconductor fuse is not a special fuse made of
silicon. It's a very fast-acting fuse designed to protect power
NEC in the Facility
The maximum rating of an overcurrent protective device
(OCPD) for a motor depends on the type of OCPD and the type of motor.
Taking these variables into account, Table 430.52 provides four columns
of multipliers to use on the Full Load Current (FLC) so you arrive at
the correct maximum rating.
When safety may be in doubt, do you voice your
If so, great. But are you looking for someone to tell you it's OK, or
are you trying to ensure you've identified the possible safety
problems? Don't accept an answer just because it makes things easier
or conforms to your earlier idea of what conditions probably are.
the explanation only if it comes with verification.
A good answer to a safety question involves proving that something
safe. And that begins with asking the right question. "Did you lock it
out?" is not the right question. Instead, ask, "Can you walk me
through the system, and show me how you identified all possible energy
Electrical Troubleshooting Quiz
You know safety can't be compromised, and you don't
want to be the one responsible for increasing downtime. It appears,
however, that you must make a trade-off between job efficiency, safety,
and uptime. Fortunately, things aren't always as they appear.
One solution is to reduce the scope of your department's
responsibilities. For example, outsource certain tests. Or, outsource
some of the construction work that maintenance gets saddled with. But
expenditure approvals and other obstacles might be in the way.
Now, revisit the fastener issue. Would replacing those slotted head
screws with Phillips-head or Torx screws void the
listing or approval? Probably not, but run this by the manufacturer to
be sure. Then, invest in the industrial-grade, battery-powered
screwdrivers with industrial bits. Instead of twisting each screw by
hand, you can zip them in and out almost instantly.
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