|
|
Maintenance
The Power of
Information — Take 3
These three information sources are vital to
cost-efficient maintenance:
- Equipment service manuals. Avoid guesswork and costly
mistakes in application, setup, programming, and spare parts. Review
each maintenance procedure against the manual to eliminate unnecessary
maintenance and add what’s missing.
- Troubleshooting guides. If the manufacturer doesn’t
provide
a troubleshooting flowchart, create your own with input from
technicians
familiar with the equipment. The better you can document the process of
resolving downtime issues, the shorter downtime will be.
- Operational instructions. Are operators using the equipment
correctly? Can maintenance people run it through its paces after a
repair?
Motor Maintenance
Tip, Part 14
Moisture can cause a motor to run hot if it penetrates
the insulation and creates parallel leakage current paths. Sometimes,
the motor is so wet it can’t even start — the insulating material
fails, and you have shorted winding conductors.
A motor may be wet due to condensation. You can prevent condensation
by installing a motor heater. Or, a motor may be wet because an
operator
hosed water into the motor vents. You may need to use a totally
enclosed
motor to prevent recurrence.
Don’t run a wet motor to dry it out, or you may permanently damage
the insulation. If you suspect a motor is wet, dry the motor without
running it. A common approach is to use an insulation resistance
tester, but consult your motor service manual (or the manufacturer) for
specific recommendations.
ADVERTISEMENT
 Nylon Liquid Tight Strain Relief Fittings
Starting at $0.40, elecDirect Nylon Strain Relief Connectors are always
in stock. Available in NPT, PG, and Metric threads, all connectors are
UL Listed, CSA Approved, and meet IP68 specifications for liquid tight.
elecDirect stocks more than 13,000 electrical products and tools. Use
Coupon Code ‘MRO608’ at checkout to receive 10% off your next
order.
www.elecDirect.com
— or call toll free 800-701-0975
Repair
Electrical
Troubleshooting Quiz
Motor starting problems and outright failures began to
occur frequently not long after a new VP of operations came onboard
and
started an aggressive cleanliness campaign.
You’ve always had weekly washdowns in the production area, and
these haven’t caused a problem before. You suspect the operators are
now washing more vigorously and getting water into the motor vents.
Yet,
the failed motors are dry when you replace them. How can you tell for
certain if water is the problem?
The answer to this question appears at the end of this
newsletter.
Circuit Breaker
Repair Tips — Take 3
A visual inspection of a breaker that has been in
service for a long time is likely to reveal contacts that don't look
quite
right. Naturally, you want to fix this. That’s a repair, and you want
to do it correctly.
Before cleaning the contacts or tightening the connection
points:
- Take “as-found” contact resistance readings.
- Review the “as-found” readings against the manufacturer's
specifications.
- Check alignment. Contacts should be centered on each other.
- Clean the contacts. If it takes more than a light sanding to clean
up the contacts, replace them.
After cleaning and alignment:
- Take “as-left” contact resistance readings.
- Lubricate per the manufacturer's recommended procedure.
- Manually operate the breaker again.
If the above steps aren't enough to place the readings within
specifications, contact the manufacturer's support department. If you
put the breaker back in service, you won't be any worse off than you
were before the maintenance work. However, you don't have assurance
that
the breaker is serviceable. If you can replace this breaker at this
time, do so.
Fuse, Interrupted
Know the fault level (for the nominal circuit voltage)
and the current that is available at the line terminals of the
equipment
before selecting a fuse. Per 110.9, a fuse must have an interrupting
rating sufficient for these two factors, if you intend for it to
interrupt at fault levels.
Operation
NEC in the Facility
You need to be able to disconnect motors and
controllers
[430.101]. Provide a disconnecting means for each controller, in sight
from the controller location [430.102]. Article 100 defines “in
sight.”
Identify Critical
Equipment
This is the equipment that, if it fails to operate
normally, causes one of two conditions:
- It fails to protect people, property, or your key processes from
serious threats.
- The misoperation itself presents a serious threat to people,
property, or your key processes.
Any system that falls under NEC Art. 700 or 701 (emergency systems and
legally required standby systems) obviously is critical. So is any
system that has to do with fire alarms, fire suppression, and emergency
communications.
Parts of systems can be critical, even if the system itself is not.
For example, a pressure relief valve keeps a non-critical vessel from
rupturing and leaking acid.
Safety: Spreading the Word
You may have heard the expression, “Safety is no
accident.” Part of the message being conveyed is you must take an
active role in safety meetings, discussions, and training.
Simply being quiet but inattentive won’t make you safer. People
learn a little by osmosis, but real learning comes from participation.
Think of how you learned how to perform electrical work. You didn’t
just show up and hope something sank in — you asked questions and
solved problems. Those problems may have been assigned by your teacher
or may have been actual problems, but they were problems you dealt
with.
Learn safety the same way. When you are at a safety meeting or in a
safety training session, ask questions and seek advice.
Also, managers can’t be everywhere. Use these meetings and
training
sessions as a chance to mention concerns, unsafe acts, and unsafe
conditions.
Show & Events
Learn About the Changes in the 2008 National Electrical
Code®
In two informative and interest-filled days with Mike Holt,
you'll learn about major NEC® changes that will impact
your work,
whether you're an electrician, contractor, engineer, designer, or
plant/facility maintenance person. You'll also earn continuing
education
hours and professional development hours.
Two conferences are scheduled for 2008:
PORTLAND, OR: September 4-5.
SAN ANTONIO, TX: September 8-9.
For more information and to register online, go to http://CodeChangeConferences.com
Quiz Answer
Answer to
Electrical Troubleshooting Quiz
A wet motor can start and run if it’s not too wet.
But
this doesn’t mean all is well. Most likely, enough water is splashing
through the vents to wet the insulation without soaking it. You don’t
have a direct short, but you do have leakage around and through the
insulation.
This leakage causes permanent damage to the insulation. Although the
wet motor runs, dries itself, and appears not to have a moisture
problem, moisture is, in fact, destroying the motor.
Start by taking baseline insulation resistance (IR) readings on the
suspect motors. Then, take IR readings daily and trend the readings. If
you don’t have power anomalies degrading your insulation, the trend
will slope so little that it will appear to be a straight line. If the
trend dips on the day following the washdown, you have identified the
problem.
|
You are subscribed to this newsletter as #email#
For questions concerning delivery of this newsletter, please contact
our
Customer Service Department at:
Customer Service Department
EC&M
A Penton Media publication
US Toll Free: 866-505-7173
International: 847-763-9504
Email:ecmweb@pbinews.com
Penton Media, Inc. | 1166 Avenue of the Americas, 10th Floor | New York, NY 10036
Copyright 2013, Penton Media, Inc. All rights reserved. This article is
protected by United States copyright and other intellectual property
laws and may not be reproduced, rewritten, distributed,
re-disseminated,
transmitted,
displayed, published or broadcast, directly or indirectly, in any
medium
without the prior written permission of Penton Media, Inc.
|
|
