Circuit Breaker Injection
Partial Discharge Testing
Sample Inspections Reduce Repair
NEC in the Facility
Answer to Electrical
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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.
Because circuit breaker injection testing is so
beneficial, many facilities incorporate it into their regular breaker
maintenance program. That makes good sense, but only if a qualified
person does the actual testing. Otherwise, you have accuracy and safety
issues. You may need to outsource to an electrical testing firm to get
such a person. This will be someone who:
Injection testing has three variations:
- Uses special test sets for this purpose.
- Is trained to conduct this test on the specific breaker under test.
- Has sufficient knowledge to be able to understand the equipment and
systems related to that breaker.
Which variation is best? That depends on your circumstances. Discuss
with your testing team the merits of the three variations for your
specific application, based on present conditions. The biggest cost
component of this testing is the shutdown that interrupts production.
limit this cost, you should plan well beyond the actual work.
- Primary injection, which is more thorough than secondary.
- Secondary injection, which is safer and faster than primary.
- Secondary injection with primary verification.
Plan for mobilization, setup, cleanup, and contingencies. Prepare
such things as temporary power, temporary light (don’t forget
bathrooms), fuel, lifting gear, ladders, security, access, spare parts,
test equipment, working clearances, testing areas, repair areas, hand
tools, power tools, lockout/tagout, equipment manuals, system drawings,
and first aid. Also, don't forget to coordinate with affected
departments, contractors, and suppliers.
Insulation “weak spots” progressively deteriorate
until they are finally breached by a partial discharge (PD) of current
from the conductor to the surrounding air. Although this discharge is
invisible to the unaided human eye, with PD testing you can see where
these weak spots are located. Regularly scheduled PD testing for
medium-voltage (MV) and high-voltage (HV) power distribution lines
allows you to make repairs before those lines fault.
PD testing also is worthwhile for equipment operating at those
voltages, such as transformers and switchgear. It’s especially
valuable for motors or generators operating at MV or HV levels.
Eventually, the insulation in this equipment will exhibit partial
discharge. You can’t prevent it.
PD in motors is a bit like harmonics in that you can tolerate some,
and it’s not cost-effective to try to eliminate all of it.
Nevertheless, you can keep things from lurching into the disaster zone
if you combine regularly scheduled PD testing with long-term trending
(on the order of years).
For cabling, switchgear, or transformers, PD tolerance is different.
In fact, it’s zero. Once you can detect PD with those items, outright
failure is in the near future.
101 uses for the new Fluke 416D and 411D Laser Distance
Best-in-class tools take you long distances,
beyond hard-to-reach areas and through time-consuming calculations,
laser accuracy. You can use the Fluke distance meters in dozens of
electrical, industrial, and HVAC applications. Go to www.fluke.com/101uses to find
out all 101!
Small motors don’t seem to last in your facility.
Exhaust fans, HVAC blowers, mixers, conveyors, and door openers need a
new motor within just a couple of years.
You read that sending a small motor to a motor shop for forensic
examination can help identify a root failure cause when failures are
widespread. So, you send a couple of failed ones out.
The motor shop informs you the bearings are severely pitted. What
problem does this indicate, and what condition is most likely causing
The answers to these questions appear at the end of this
Reduce Repair Demand
Nobody questions the wisdom of having a motor shop
perform a forensic examination of motors that are expensive or used in
critical applications. In many facilities, however, the policy is to
regard failed non-critical motors below a certain size as
“throwaways.” On a per-motor basis, the cost justification
considerations make sense — but not on a facility-wide basis.
If motors are failing due to some unknown root cause, you’re
replacing motors unnecessarily. When you do ROI calculations across 10
motors instead of one, the cost of that forensic examination is
Look at your motor population, and determine a good sampling rate
sending “throwaways” out for forensic examination. If any
failure cause is a mystery, then send that motor out regardless of the
sampling rate — the inevitable second mysterious failure will double
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NEC in the
Although the demand for stationary batteries has
exploded in recent years, you don’t want your batteries to do
likewise. Conducting maintenance per the manufacturer’s
recommendations is essential for preventing this.
So is adequate ventilation, as required by 480.9. The NEC, not being
a design guide [90.1], doesn’t define “adequate.” However, other
references do. Contact your battery manufacturer if you need to
the applicable installation standards.
You’ve heard the expression, “Dress for success.”
One of its meanings is that shabby shoes say volumes about you. The
goes for a faded shirt or tattered jeans. But when you’re in the
gritty, “get-dirty” environment of facility maintenance, does your
dress code really matter to your success? The simple answer is yes.
More importantly, clothes take on added significance when performing
- Clothing that is torn can create an easy snagging hazard. Clothing
that is thin offers little or no skin protection.
- Unserviceable shoes can cause problems with your back, knees, and
even your neck.
- Synthetic materials can carry a burn deep into tissue. To avoid
inadvertently wearing synthetics on the job, eliminate polyester and
other synthetics from your wardrobe; read the labels of all of your
shirts, pants, jackets, and underclothes.
Fluke 289 Industrial Logging Multimeter Maximizes Productivity
in the Plant
The Fluke 289 True rms DMM features a logging function with expanded
memory that stores up to 10,000 readings for unattended monitoring of
signals over time. Users can save multiple logging sessions before
download is necessary and review logged readings in graphical format
directly on the meter display using on-board TrendCapture
capability. Available from authorized Fluke distributors. click here to learn
Electrical Troubleshooting Quiz
Severe pitting in bearings is a classic sign of
undesired current flow through them, which in turn indicates a bonding
deficiency. The undesired current doesn’t have the required low
resistance path back to its source [250 Part V], so an inordinate
flows through the bearings.
Solve the pitting problem, and the subsequent motor failures, by
applying Art. 250, Part V to all electrical equipment. Here’s a
“find-it-fast” clue. Look for a driven rod on the load side. That
location is probably missing a proper bonding jumper.
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