Motor Maintenance Tip, Part
Fuses and Motors
NEC in the Facility
Answer to Electrical
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The designations "National Electrical Code" and "NEC" refer to
National Electrical Code®, which is a registered
trademark of the National Fire Protection Association.
How well do you perform these three critical functions
- Qualifying personnel. OSHA and the NEC both provide
definitions of “qualified.” In a nutshell, a qualified worker has
the necessary training and experience to competently (and thus safely)
execute the assigned task on specific equipment or systems.
- Providing procedures. Good procedures outline the major
and identify the critical ones. They provide cautions, references, and
advice (one common approach is to tie these to “stop points”).
Don’t use generic cautions — provide cautions on working with the
safeguards, interlocks, and alarms for that particular
Your procedures should identify any special needs in test equipment,
tools, PPE, or materials. They should identify special precautions
(e.g., venting), permissions needed (e.g., operations supervisor), and
permits needed (e.g., confined space) for the specific tasks involved.
- Reporting. Reports on completed work need to show “as
found” (measurements and other data pertaining to the equipment
condition), work done, test equipment used, and “as left.” They
should include observations (e.g., breaker meets specs, but operation
was stiff) and recommendations (e.g., breaker needs inspection before
normally scheduled next inspection to see if exercise and lubrication
fixed the problem). Every report form should include a space for safety
concerns and problems encountered (e.g., guard missing on cutter, key
didn't work, had to move clutter from in front of
Tip, Part 17
Proper bonding at the motor is critical, but there is
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flashovers or currents from circulating through your bearings. That’s
what bonding [Article 100] is for. Grounding does neither of those
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A mixing system under PLC control experienced
oscillations and then process runaway on the backshift. Now, a few
later on dayshift, the system is responding sluggishly and scrap rates
You consulted the logbook and found the responding technician merely
noted, “Adjusted program. Stopped and restarted system. Monitored for
oscillation, but found none.”
- What is wrong with that log?
- Where do you start to determine what is wrong with this
The answers to these questions appear at the end of this
Which maintenance tech effectively responds
faster to a conveyor failure call?
- Tech No. 1 arrives in 30 seconds with a screwdriver and pliers.
- Tech No. 2 arrives after first going to the shop to obtain a tool
pouch, DMM, and the applicable repair procedures.
- A screwdriver used for any purpose other than turning screws is
dangerous and inevitably becomes worthless as a screwdriver.
- Changes made without “as-found” and “as-left” measurements
defeat any effort to know the problem is actually fixed.
- Unless Tech No. 1 resorts to the “wing-it” method, Tech No. 1
will walk to the shop and back for the needed tools, so he or she is
actually slower than Tech No. 2.
Fuses and Motors
You need to account for the type and class of fuse when
selecting the current ratings of fuses for individual motor branch
short-circuit protection. Use Tables 430.248, 249, and 150 to select
NEC in the
In the typical facility, there’s an ongoing battle
adequate equipment closet space. One of the casualties of this battle
the distribution transformer.
The unlucky transformer is often jammed into a small room. Open the
unventilated door, and the heat just rolls out. Sometimes, the
transformer vent faces the back of a cabinet or some other obstruction
placed there after installation “to save space.” That condition can
lead to a catastrophic failure that opens far more space than intended
— complete with smoldering trails of vaporized metal.
How can you argue persuasively for adequate ventilation? And how
is adequate? Most facilities are insured. Insurers nearly always
conformance to the applicable standards. For transformer ventilation,
that is 450.9 of the NEC. In 450.9, you’ll find how much ventilation
is adequate and other related requirements.
But the 450.9 requirements are only the minimum for safety.
They do not address efficiency. In this era of green initiatives,
adequate ventilation is not enough. It’s likely, however, that
the incremental increase in ventilation to produce the desired energy
benefits isn’t much. Start with 450.9 and look for inexpensive ways
optimize ventilation from there.
Your safety responsibilities probably extend to people
who don’t even work for your company — such as visitors to your
administration buildings or children who trespass onto your company’s
If your facility is near a school or apartment complex, look for bent
fencing and other signs of entry. If children are nearby, consider a
“talk with the kids” event so kids understand why they need to play
elsewhere. The local police department is an excellent resource for
- Secure doors and gates.
- Secure mechanized equipment, power tools, vehicles, and toolboxes.
- Lock carts and vehicles, and remove the keys.
- Lock out unused circuits.
- On energized circuits, coordinate with the engineer in charge of
each system to apply breakaway locks as needed.
- Erect proper barriers and signs.
Electrical Troubleshooting Quiz
The answer to the first question is easy. That
technician didn’t leave any data (e.g., “as found” or “as
left”). The notes on the “repair” aren’t clear, either. What
the programming change? Why was it made?
Your first step will be to do the documentation the night shift tech
should have done:
The program of a PLC system doesn’t “go bad,” so changing the
programming when there hasn’t been a configuration change is almost
always a bad idea. A programming change may disguise a problem
temporarily, but it’s not a fix. So, restore the original
Then, check the inputs and the final control elements — where you
likely find the culprit.
- Take as-found measurements. Measure the applicable variables
(e.g., input sensor levels, voltage supply, controller output) called
for in the repair procedure (or PM procedure) for that system.
- Document programming changes. Compare the new programming to
the original and record the differences.
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