Suppose you measured 485V at the supply of a motor and 430V
at the motor. Your voltage drop calculations show that voltage at the
motor should be 470V if there are no losses in cabling or connections.
Congratulations. You've discovered power distribution system maintenance
problems that are reducing motor life. You have serious losses in the
cabling and/or connections. These problems probably exist well beyond
that one feeder.
You can use thermography to find high-loss connections. But if
you just go in and repair those, you may end up doing that work twice.
Yes, identify those connections; they will have to be replaced. Before
you replace them, perform insulation resistance testing on the feeder
After you replace defective cabling and connections, repeat the
insulation resistance testing to get baseline readings. Why is this
important? Because those readings will allow you to properly trend
readings when you do the "lessons learned" thing and make cable testing
part of your predictive maintenance program. Thermography, too, will be
part of any sound program.
grip on accuracy.
62 Mini non-contact thermometer is the perfect introduction to
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Strange things have been happening in the plant lately.
Rumors are circulating about sabotage and industrial spies. Many
operators refuse to work at particular machines. Among the many
Corporate issued a memo to "ground all of the machines." Your boss
handed you the work order and wants you to start installing ground rods.
How should you respond?
- Three different drinking fountains routinely
- Machines sometimes shut down in mid-run for no apparent
- Red (stopped) and green (running) lights are on simultaneously,
though one's dimmer than the other.
Visit EC&M's website
to see the answer.
Previously, we said a neutral-ground (N-G) bond might be
upstream of the receptacle where measurements indicate the existence of
the bond. We also said that if you didn't find it at the supply panel to
check the other equipment on that panel. Fixing this in an efficient
manner will require some scheduled downtime. Using the panel directory,
you can probably identify the connected loads; however, verify with
current drawings. Then, ensure the wiring for each circuit is properly
and accurately labeled.
Arrange to do the work when production shuts down for lunch,
between shifts, or at some other time the affected production manager
agrees will minimize interruption of production. The amount of time
required will depend on how many circuits are on that panel.
To read more on this story, visit EC&M's website.
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Commonly misunderstood/misapplied terms, part
- Overload. When you're working with circuit
protection devices, keep clear in your mind what this term means. Don't
confuse an overload with a fault. They aren't the same thing, and
protection against one isn't necessarily protection against the other.
Overload means operating equipment in excess of its normal, full-load
rating (or pulling more current through a conductor than its ampacity
permits), when sustaining this long enough would result in damage or
- Plenum. If you don't understand the layout of the air
distribution system in a structure, you could inadvertently run
non-plenum-rated cable in a plenum. A plenum doesn't have to be enclosed
in sheet metal. The inside space of a wall might be a plenum. An example
is the "in the wall" cold air return commonly used in residential
dwellings. If an air duct connects to a chamber (or compartment), then
that chamber is a plenum.
- Qualified person. Being given a task and being qualified
to do it aren't the same thing. Nobody wants a botched job or an
industrial accident, so speak up if you don't have the skills,
knowledge, and safety training a particular task requires. Some tasks
may require equipment-specific knowledge. Evaluate each assignment to
ensure you’re qualified to do it.
Understanding the purpose of each of the eight sections of a
material data safety sheet (MSDS) will help you quickly and efficiently
get the information you need about whatever chemicals you're using. The
first section is "Identity," and it provides the various names the
chemical is known by (including street names and trade names). It also
provides the contact information for the manufacturer of this chemical.
Chemical Abstract Services is a company that distills down all of
the information on a given chemical into an abstract and then assigns
that chemical a CAS number. This number is often helpful to emergency
response personnel. If an EMT asks you for this number, you simply have
to look in this part of the MSDS. The emergency phone number for this
chemical is in this section also. If you call it, the operator will
probably ask you for the CAS number.
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