Maintaining the Motor
Electrical Troubleshooting Quiz
Replacing Motor Drives
Replacing Motor Starters
NEC at the Facility
The Practical Implications of OSHA 1926.416
Answer to Electrical Troubleshooting Quiz
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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
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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.
Maintaining the Motor
Motors are critical components of larger systems. You
don't run a motor just to run it. You run a motor at a certain speed
at a certain time to accomplish a specific goal. A mixer motor might
on high speed for 1 minute, and then maintain a low speed to keep the
mixture from separating. A conveyor motor may stop and start to move
parts from station to station.
All of these applications require properly functioning motor
controls, or they fail. At a minimum, you should perform these motor
control circuit tests on a regular basis:
Perform any preventive maintenance required for the motor drive.
- Test the e-stops for operation. This is the most critical part of
motor control maintenance, because e-stops protect people.
- "Walk down" the circuitry and look for loose connections, foreign
matter, and discoloration.
- Check fasteners, including mounting hardware. If the controls are
an enclosure, check the backplane and any other mounting surfaces.
- Manually engage the starter. If you measure more than 0.1 ohms
across the closed contacts, replace all contacts in the starter.
- Perform an insulation resistance test to ground of starter, from
power side to ground. Repeat from the load side to ground. If you have
less than 2 megohms, replace the starter.
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By Mark Kenyon, low-voltage drives engineer,
Inc., New Berlin, Wis.
A motor drive that performed flawlessly for several
years has suddenly failed. This was on a critical line, so you had a
spare. You swap out drives, and quickly bring the line back up. But
the new drive fails. You open it up and see bulging capacitors. What
could have caused this?
The answer to this question appears at the end of this
Replacing Motor Drives
Motor drives are reliable, but they can fail. Often,
point of failure is a transistor (SCR in the older drives) --
typically an IGBT. A quick replacement, and you're up and running, but
the failure can be more severe, requiring a total drive replacement.
A drive upgrade is almost always beneficial. Motor drives keep
getting better, smaller, and cheaper. Each new generation solves or
reduces some problem in the previous generation.
With all the various motor drives on the market, how can you pick
right one? Contact your electrical supplier or the drive manufacturer
for assistance, and have this information ready:
With this information, your distributor or manufacturer can help you
make the best purchase. Now is also a good time to check the
of that drive. Look for voltage imbalance and other issues in the power
supply. Ensure the "ground" wiring to the drive is properly bonded so
electricity has a path back to the source (not to a ground rod).
- Nameplate data from the motor
- Nameplate data from the existing drive
- Cable distance between the drive and the motor
- Photo of motor and drive, as installed
- Brief description of the application
- Brief description of the failure and what you found per the
troubleshooting steps in the manual.
Replacing Motor Starters
Mass changeouts provide a great upgrade opportunity.
example, suppose changes in your company's products have resulted in a
project: You've got to reconfigure a conveyor system and some other
equipment. Part of this project will involve replacing several 10-hp
motors with 25-hp motors. Simply replacing the existing starters with
larger ones might be short sighted.
You may want to look at what your electrical supplier has in the way
of starters or other motor controls. You may find some connectivity
features, for example, that allow you to provide input via your network
to an operator console. Or you may decide on a different model of
starter that provides more compactness and will allow you to centralize
starters in a common cabinet. If you've got individual starter
enclosures scattered all over the production floor, consider
consolidating these into a central location to reduce footprint
You could do that with NEMA starters or with IEC starters.
For Quick Motor
Decontactors are a combination plug & receptacle and disconnect
switch. They allow electrical equipment to be safely and easily
disconnected and connected - up to 60 hp or 200A. Since there is no
access to live parts workers can change out a motor without having to
'suit-up'. Inquire about our free trial program.
Meltric Corporation, call 800-433-7642, www.Meltric.com
NEC at the Facility
What's the difference between Art. 280 and Art. 285,
what does it mean for your facility? To answer that, you need to know
the difference between surge arresters and surge suppressors.
Surge arresters limit surge voltages by discharging or
bypassing the current. Surge suppressors limit transient voltage by
diverting or limiting the current. These are distinctly
methods that accomplish distinctly different goals.
Difference in application: Surge arresters prevent the
from rising above a level the suppressors can handle. Surge suppressors
then reduce the voltage to a level the equipment can handle.
The typical application for surge arresters is before the service
(e.g., a spark gap arrester), to prevent large transients from entering
the facility. Surge suppressors (e.g., TVSS device), which are
applicable only to circuits of 600V or less, are used downstream of
From an engineering standpoint, applying Art. 285 without any Art.
280 protection exposes the TVSS to more energy than it can handle. To
avoid sacrificing both equipment and TVSS, start with a one-line and
note the points where each kind of protection applies. For TVSS, you
will probably need multiple units at staged energy levels for
The Practical Implications of OSHA
This passage focuses on the idea of protecting
from energized equipment. Some of the key points include:
- If you must work near a circuit with which you could make contact,
de-energize it and then provide proper grounding or guarding.
- When removing fuses, use a tool rated for the voltage.
- Keep workspaces and walkways clear of cords.
- Don't use frayed cords.
- Don't fasten extension cords with staples, hang them from nails, or
suspend them with wire.
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Answer to Electrical
You might be tempted to assume both drives failed for
the same reason, but that's not what happened. The observation that "it
performed flawlessly for years" is a clue that the first drive failed
probably due to a power event or other transient cause. This is also a
clue as to the age of the replacement drive. Capacitors hold a charge
for only so long. Before putting a spare drive online, you need to put
the DC link capacitors through a recharging process. Consult your drive
manual or the manufacturer for information on how to do this.
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