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CONTENTS
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Optimize How You Handle
Spare
Parts
Motor Maintenance Tip, Part
5
Electrical Troubleshooting
Quiz
Reducing Repair-Induced
Failures
NEC in the Facility
Safety
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
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Maintenance
Optimize How
You
Handle Spare Parts
Your company needs to reduce inventory costs, but you
can't allow production to stall due to lack of a critical spare part.
To
balance these opposing needs:
- Review the min/max on spare parts. Proper quantity levels may have
changed, due to changes in sourcing, lead times, and quantities used.
Some parts may no longer be necessary.
- Reduce re-ordering. Get off the replacement treadmill of high-usage
spare parts. Solve root causes of the failures that drive the
re-ordering (thus raising min/max). Solutions can include everything
from power quality improvements to equipment redesign (in consultation
with the manufacturer).
Caution. If repair logs show that only one component in an
assembly fails, you may be tempted to reduce inventory costs by
stocking
that component instead of the entire assembly. Before you do that,
determine whether downtime will increase because of the complexity of
installing that component versus the assembly.
Supplier tip. Focus on value, not price. Which supplier is a
better bargain? The supplier who took your call at 2:00 a.m. and had
someone there at 3:00 a.m. with the one critical fuse you needed, or
the
discount supplier you can't reach at night? Let your purchasing people
know which suppliers provide added value and in what ways.
Motor Maintenance
Tip, Part 5
Single phasing (loss of one phase of a 3-phase system)
produces significant heat in the motor. If a motor is overheating for
no
apparent reason, check the current draw on all three phases. If one
phase is near zero (the other two carry the load), then you have single
phasing.
The cause of the single phasing is probably a bad contact in the
motor starter, but it could be something else. In one application, an
open supply fuse combined with an inadvertent backfeed to create a
single-phasing problem.
Monitor for single phasing. Overload protection is not intended to
protect against a single-phase condition (it could, incidentally, if it
conformed closely to the motor's heat curve). However, you can buy
standalone protection units that detect single phasing and provide an
alarm or even shutdown action. Motor drives, soft-starts, and other
motor monitoring/control equipment often have this functionality built
in.
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Repair
Electrical
Troubleshooting Quiz
Line Three never exhibited any problems until the PLC
that controls it lost an I/O card a few weeks ago. Ever since then, the
line has displayed erratic behavior. Despite several programming
changes, the problem remains. Your boss assigned you to get to the
bottom of it. Where should you start?
The answer to this question appears at the end of this
newsletter.
Reducing
Repair-Induced
Failures
Does it ever seem that some machines are jinxed? Good
thing you have Johnny Ace on hand. He can "get it running again" faster
than anybody. But maybe he's a bit too fast. When you have a
"one-thing-after-another" problem with any equipment, suspect the repair
methods
rather than the equipment.
If you want to see whose repairs are causing failures, look at how
people treat their tools while working. Some people wipe every tool
before putting it away, and put away every tool unless they're using
it.
Other people scatter tools (and parts) everywhere while they work, and
their tools are never clean. Which person do you think pays more
attention to the details in making a repair? Which one do you think is
less likely to leave a stray dollop of grease on a drive belt or leave
a
loose washer on a busbar?
We constantly train people what to do. They use
troubleshooting techniques, employ repair methods, follow written
procedures, and apply skills learned in a classroom. Nevertheless, we
tend to drop the ball on training people how to do things.
NASCAR history buffs pay homage to Red Vogt, the great mechanic
behind several legendary racers in NASCAR's early days. Vogt had a
reputation as a mechanical miracle worker. Not only was he known for
powerful engines that did not fail, but also for keeping his
work area spotless -- the two are not unrelated.
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Operation
NEC in the Facility
A pulping plant in Kentucky began to have a high rate
of
motor failures. When a consultant inspected the motor invoices, he
noticed the failures were among the same few applications. Once an
application received a replacement motor, the failure rate went
through the roof.
The replacement motors were sized properly and were the right design
for the intended load. However, they violated 430.16 because they were
normally vented. The environment was full of flying fibers, thus
requiring a totally enclosed fan cooled (TEFC) motor.
The FPN to 430.16 notes especially severe conditions may require
additional measures. That was the case with one particular application
in this pulping plant. After installing a vented shroud around the
motor, the monthly "replacement drill" ceased to happen.
Safety
How do you identify the energy source(s) of a piece of
equipment for purposes of lockout/tagout? Suppose you locate the
electrical drawings for a large press and identify the breaker that
supplies power to the drive motor. You lock the breaker open and tag
it.
This action, while essential, doesn't mean the press is
de-energized. It merely means the drive motor is de-energized.
Be
sure to account for mechanical springs and hydraulic cylinders, which
can store energy. Another energy source is position. On a press, for
example, the top die can't possibly fall on you if it's already all the
way down.
Quiz Answer
Answer to
Electrical Troubleshooting Quiz
Find the backup of the "pre-problem" programming, and
restore the programming as your first step. This eliminates one set of
variables. Programming doesn't change on its own, so doing programming
mods doesn't solve for failure.
You need to look at the work surrounding the I/O card replacement,
which is when the erratic behavior started. The most likely cause is
either a loose connection in the sensing loop or a damaged sensor. Walk
down the control loop and look for what someone might not have put back
together properly when simulating the input to that loop during the I/O
card troubleshooting process. Find out who replaced that I/O card, and
show that person what you found.
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