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CONTENTS
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Cast
Your Vote Now!
The Power of Information
Motor Maintenance Tip, Part
12
Fixing "Repair to Fail"
Clear Up Semiconductor
"Con-fuse-ion"
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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Maintenance
The Power of
Information
To properly support your maintenance and repair
efforts,
your maintenance system needs certain information for each piece of
equipment. For example:
- Nameplate data. Here’s a tip overheard at a NETA
conference: Photograph the nameplates with a digital camera. This
eliminates any chance of a transcription error, and it saves time.
Nevertheless, it has its limitations — you may need to capture some
of
the nameplate data as text, and that means additional steps. This
situation may arise, for example, if you’re using motor application
or
maintenance software that uses nameplate data for calculation purposes.
- Equipment purpose and use. A summary of what a specific
piece
of equipment does will help people correctly interpret the drawings and
other documentation. The person working on the equipment should
understand precisely how it interacts with the system that it is a part
of. A lack of such understanding is often mentioned in fatality
reports.
- Location of equipment and controls. Obviously, this prevents
the time drain of looking for things. But there’s another important
advantage to doing this. Listing the controls and where they are makes
it far less likely someone will overlook an energy source and
consequently fail to lock it out.
- Equipment drawings. The electrical ones include wiring
diagrams, interconnection diagrams, schematics, power source drawings,
and controls drawings. Non-electrical drawings, such as piping and
installation, may also apply.
In our next issue, we’ll look at some other kinds of information that
can help you maintain equipment more efficiently and safely.
Motor Maintenance
Tip, Part 12
If motor maintenance or repair tasks involve stopping
and starting a motor, remove as much load as possible. It’s often
impractical to mechanically decouple the load, but you may reduce the
load in other ways.
Examples include:
- Remove product from the conveyor before testing drive motor
operation.
- Remove product from the mixing vat before testing the agitator
motor.
- Start a large air compressor motor in some phase other than the
high-demand loading phase.
- Start a pump without deadheading it. With large pumps, deadheading
can destroy the pump.
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Repair
Fixing "Repair to
Fail"
Some equipment seems to be jinxed with breakdowns.
It’s just one thing after another. Is there some kind of voodoo going
on?
Most likely, the new failures have resulted from errors made during
maintenance or an earlier repair. Consider these examples, and think
about how “maintenance errors” might be cropping up in your
equipment:
- Jim fails to clean the zirc before greasing a motor. Two months
later, the thrust bearing fails.
- Mitch steps on a cable, damaging the insulation. The cable fails
prematurely and unexpectedly.
- Bob jogs a motor in reverse before forward motion has stopped. The
gearbox starts rattling a few days later.
Clear Up
Semiconductor "Con-fuse-ion"
A dual element fuse does not give you two shots at
overload before it opens. The two elements are in series with each
other, not parallel. Dual element construction allows each element to
dissipate some of the heat, so it’s typically used to achieve a time
delay.
Operation
NEC in the Facility
Eliminate ground-related starts. It’s a good idea to
analyze the control logic on your motor control diagrams. Look at the
return paths. Is one side of the motor control circuit grounded
(meaning
bonded, not an earth connection — see Article 100)? If so, you must
ensure that an accidental bonding connection won’t start the motor or
bypass manual controls or automatic safety devices [430.74]. For motors
on production lines, it’s a good idea to test all of the E-stops to
confirm the entire system meets this requirement.
Safety
In many companies, the effort is on safety
compliance. This sets the stage for a dangerous game of “not
getting caught.” A sure sign of a safety compliance mindset is when
people put their safety glasses on as they see their supervisor
approaching.
It’s much better — for each individual personally — to be
proactive. Make a conscious effort to protect yourself, other people,
and property on/near the job site. Ask, “What could go wrong?”
Then, think about what procedures you need to follow to either prevent
it from happening or keep you safe if it does.
Quiz Answer
Answer to
Electrical Troubleshooting Quiz
This isn’t how an E-stop works. Although it may look
like a momentary contact button, it’s not. The way it must work is
this: When someone mashes an E-stop, the system shuts down. It can’t
restart until someone physically resets that E-stop. If you have any
other arrangement, it’s unsafe.
Because those E-stops aren’t “locking down” this system, you
need to test each E-stop to ensure it’s working as intended. If they
are 120V E-stops, test them at 120V. Replace any that don’t function
correctly.
Next, look closely at the control logic to see if the E-stops are
incorrectly being used as control inputs. An E-stop is not a stop
button
in the start/stop logic of a motor control system. It’s a physical
permissive in series with it. Make absolutely sure there’s no bypass
around any E-stop. If so, change that immediately.
Another question is, “Why is this system restarting on its own?”
To answer that, thoroughly review the system logic. The control logic
of
the motor controller should not allow an automatic restart. The control
logic for the system (controller, E-stops, and any other controls)
should prevent such a restart.
Walk through the controller logic to ensure it complies with 430.74.
If it doesn’t — and that is probably the case here — then a
“ground” (bonding) connection is completing a “line” in the
control circuit. The problem isn’t the fact that connection exists.
The problem is that the system can start due to that connection.
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