Do You Have a Calibration
Motor Maintenance Tip, Part
Reassembly During Repair
Fuses for Motor Controls
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
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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.
Do You Have a
Although today’s test equipment is highly reliable,
can go out of calibration over time. Depending on the use of the test
equipment, this could be a problem.
For example, if you use a DMM to verify 480V transformer
a deviation of 0.01V isn’t going to matter. But if you’re checking
the sensors for a process control system, this could mean the
between good product and scrap.
If you don’t have a test equipment calibration plan in place,
assess the maintained equipment to see if one is necessary. If you have
tight tolerances, safety related systems, or critical trending (e.g.,
insulation resistance on critical cables), it probably is.
If you have only a few instances of “calibration advised” in
facility, you could cut costs by assigning specific test equipment to
those specific instances and then following the recommended calibration
frequency on just those items. Adding that test equipment to your CMMS
will prevent “forgetting” when the calibration is due.
Another option is to outsource the tests that require calibrated
equipment. If you do that, ensure the testing firm provides calibration
records of the test equipment being used. Come to an agreement of how
handle retesting in the event that test equipment is found out of
calibration after your tests are completed.
Tip, Part 19
You can have a motor-killing voltage imbalance at the
panelboard or at the motor control center (MCC), due to loose or poor
connections. A feeder wire joint that is dirty, loose, or corroded will
have resistance the other wire joints don’t have. The voltage drop
across this bad wire joint subtracts from the system phase voltage and
results in voltage imbalance at the load.
Don’t overlook voltage imbalance at the motor. The same loose
problem can hit here, not just at the MCC. At the motor, you have more
to look for. Consider the contacts within the circuit breaker, motor
starter, or drive. Look at lugs and T-leads.
In any of these cases, make your phase-to-phase voltage measurements
with the motor running. Begin at the easily accessible motor controller
load-side lugs and proceed either upstream or downstream. Go upstream
you find voltage imbalance and downstream if you don’t. Where you
the voltage imbalance first appearing (farthest from the transformer)
where you’ll find your bad conductor joint.
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A commercial office building with 4-foot fluorescent
fixtures has had a group relamping program in place for several years.
So, until recently, there was no need for spot relamping. Over the past
few months, however, you’ve had repeated lamp failures — even in
areas that were relamped less than six months ago.
What could be causing this, and where do you start troubleshooting?
The answers to these questions appear at the end of this
After a tense period of downtime, the repair crew puts
the equipment back in service. Then someone asks, “What about these
leftover parts?” You look, and there you see a missing bracket, a
couple of washers, a spring, and some other mysterious parts that
didn’t make it back into the equipment.
Somehow, telling people to be more careful doesn’t solve the
problem of incorrect reassembly. Nor does laying out the parts exactly
as they came out (assuming you can do that), if somebody accidentally
kicks the parts. The solution that works is the same solution used to
assemble things in the first place: Use a drawing.
The equipment service manual should have exploded view drawings
and/or assembly instructions. But what should you do if it doesn’t?
You could create your own drawing on the fly, during an equipment
breakdown. However, a better solution is to go through your equipment
documentation and contact manufacturers for what’s missing. Then,
you’ll have it when you need it — and no more leftover
Fuses for Motor
To avoid confusion when sizing fuses for motor control
circuits, refer to Table 430.72(B). This provides the maximum ratings,
depending on which of three conditions apply.
NEC in the
For any indoor dry-type transformer of 112.5kVA or
ensure there aren’t any combustible materials within 12 inches of it
in any direction [450.21(A)]. The only way “around” this rule is if
there is a fire-resistant, heat-resistant barrier between the
transformer and the combustible material.
Compliance with this rule is a constant battle in many facilities,
people try to use electrical equipment rooms as storage rooms for file
boxes and fluorescent lamps. If you have this battle, make it clear to
management that the insurer requires NEC compliance, and failure to
comply may void coverage as well as incur operational losses.
Safety isn’t the personal decision many people think
it is. One person’s unsafe act endangers others. Suppose you tape up
portable cord instead of removing it from service. Then, a coworker who
isn’t even using that cord touches a surface energized by it and dies
from electrocution. Or, suppose you leave wire scraps on the floor. A
coworker slips, falls, and is permanently disabled.
Any unsafe act can have a devastating effect on a coworker. Don’t
be the unsafe person performing unsafe acts. The flipside also applies:
Don’t let a coworker be that hazardous person. Report dangerous acts
to your supervisor.
Electrical Troubleshooting Quiz
This situation involves widespread failures, indicating
a common cause such as a transient voltage. The problem is unlikely to
have been caused by a single event such as a lightning-induced
transient. You probably have an ongoing transient source, such as
equipment recently put into service.
But maybe existing equipment or cabling has deteriorated and become
source of damaging transients. That includes equipment at a neighboring
It might not be a transient voltage, after all. You may have bonding
deficiencies, due to deterioration or human error. Or, you could have
any of several types of power anomalies.
How can you find the needle in this proverbial haystack? It’s
simple: Use a power monitor. Because commercial offices typically
don’t have power monitoring systems in place (but the day will come),
use a good power analyzer or portable power monitor.
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