Motor Maintenance Tip, Part
Wringing Revenue from Repairs
Fuses for Multiple Motors
NEC in the Facility
Answer to Electrical
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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.
Circuit breaker maintenance falls into two general
Examples of routine maintenance:
- Routine. Detection of problems via routine maintenance is
preferable to detection by any other means. The basic methods are
automated monitoring and scheduled PdM/PM.
- Major. When maintenance requires interfering with
it’s “major.” So, you try to avoid doing it. When routine
maintenance reveals a problem or it’s simply the recommended time,
can no longer avoid major maintenance.
Routine maintenance doesn’t reduce the likelihood of major
maintenance. The real value of routine maintenance is that early
detection allows you to schedule corrective actions to prevent serious
deterioration or catastrophic failure.
- Quarterly, you conduct infrared analysis and visual inspections of
your feeder panels.
- Annually, you take voltage measurements at your feeder breakers.
- Automatic ground current leakage monitoring systems activate an
alarm when ground leakage current reaches some predetermined threshold.
- Periodic reports from your power monitoring service provide
recommendations for additional maintenance based on expert analysis of
trends or events.
Circuit breaker manufacturers provide recommended frequencies and
methods for routine maintenance. They also provide major maintenance
recommendations that address parts, procedures, frequency, and
to repair or replace. Ensure this information is referenced from (or
embedded into) your CMMS, procedures, and training.
Tip, Part 18
Voltage imbalance kills motors. Therefore, you need to
detect and correct three types of imbalance. One type is a system-wide
voltage imbalance (we’ll look at the other two types in a future
The most common cause of system-wide voltage imbalance is
unbalanced loading. Examine all 3-phase panels to see that
the phases are wired correctly — what may appear correct on
panel may not be the actual A-B-C phase arrangement. Although it
may take considerable effort to track down and redistribute problem
loads, it’s a worthwhile effort.
A less common cause is the transformer taps are set wrong, resulting
in different voltages on different phases coming right out of the
transformer. The solution is to reset the taps on the transformer until
all 3-phase voltages are identical.
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Occasionally when the big mixer starts, the
branch-circuit fuses blow. Yet, there are no shorts or other obvious
problems. If you replace the fuses, things run fine for several days.
The production superintendent wants the fuses replaced with breakers
so operators can just reset the breaker. What should you do?
The answer to this question appears at the end of this
Are you leaving free money on the table? Competent
production managers know the cost of each minute of downtime on each
piece of major equipment. Usually, lost revenue is the primary driver
that cost. Ask your production managers which equipment incurs the
highest downtime costs. Focus on speeding up repair time on that
equipment, making sure you tap a valuable resource: the manufacturer.
Manufacturers often provide downtime-reducing products. For
- Assemblies. Rather than dismantle assemblies to replace a
component, you can pop out the old assembly and pop in the new one. If
an assembly isn’t presently offered, discuss this with the
- Special components. See if a particular part now has an
improved version, such as “rough service” or “quick change.”
perhaps there’s a version more applicable to your application. If
these aren’t offered, discuss your problem with the manufacturer to
see what’s feasible.
- Special tools. Race car mechanics have special tools you
don’t find at any hardware store, and so should you. Manufacturers of
industrial equipment often have special jigs, fixtures, removers,
installers, and other tools that save time. If such items don’t
contact a reputable machinist to observe a repair in progress and
propose such items. You may recoup the cost of fabrication in the next
Fuses for Multiple
Where you have more than one motor on a branch circuit,
the maximum rating of the fuses (or breakers) protecting that branch
circuit is “the largest motor load plus.” The plus part is the sum
of the full-load current ratings of all other motors on that circuit
the ratings of other loads on that circuit [430.53(C)(4)].
NEC in the
During your next outage, measure the resistance between
your service transformer case(s) and any metallic items (e.g., fencing)
nearby. In each instance, you should measure the resistance of a
jumper (which is nearly zero).
If that outage is a ways off, visually check for bonding jumpers
between all metallic objects in your transformer pens. A driven rod
isn’t a bonding jumper. You want to ensure the bonding is per 250
V, and the grounding is per 250 Part VI and VII [450.10].
Who should reset or replace overcurrent protection
devices (OCPDs)? It may seem harmless to let operators reset the
and call maintenance only if it trips again or won’t reset.
However, it’s not harmless. First of all, operators aren’t trained
in operation of an OCPD or disconnect. They invariably stand in the
blast path — without PPE.
If that OCPD has tripped due to a fault and the fault is still
present, anyone operating that OCPD is probably going to be severely
injured. Only a person who is qualified to test for faults and then
clear those faults should reset or replace an OCPD.
Electrical Troubleshooting Quiz
Operators are not “qualified personnel” to work on
OCPDs — this includes resetting breakers. What the superintendent
really wants is uptime. To provide that, you need to determine
the cause of the downtime rather than be complicit in a practice that
both unsafe and illegal.
Are those fuses sized for the largest load plus? If not, then
recalculate for the correct size. This alone may not solve the problem.
Closely scrutinize the operation itself. Are the operators overloading
that mixer before starting it? Because the problem occurs when starting
the mixer, the solution may be as simple as starting the mixer with
material (or before adding material). Monitor the current draw of the
mixer under various loading scenarios before reaching any conclusions.
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