Maintenance and Energy
NEC at the Facility
Confined Entry Attendants
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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.
Which maintenance practices can you use to reduce
waste? A good place to start is your electrical service. In analyzing
what to do, it's helpful to break the service down into its major
systems or equipment types, as follows:
Don't forget power quality. Rarely does the grid provide "bad power,"
but it does happen. Your power monitoring system can tell you when a
power event occurs in the supply. Usually, you can trace supply power
glitches to specific events -- such as an across the line start of a
big motor at a neighboring facility.
- Service transformers. Begin with an oil analysis. This will
tell you a great deal about the health and efficiency of your service
transformers. It's not unusual to find severe problems in transformers
that haven't had regular testing performed. It's also not unusual to
big efficiency gains once the problems are corrected. Ask a qualified
testing firm which tests are recommended for your particular
installation. If the utility owns your transformers and is responsible
for their maintenance, don't be penny wise and dollar foolish. Have
maintenance performed, even if you must pay for it. The energy savings
alone will probably pay for the maintenance. More importantly, a lack
this maintenance can result in a costly and extended outage.
- Service conductors. If the cables are accessible, begin with
infrared testing to reveal energy losses in the form of heat. Hi-pot
testing will show the insulation integrity (or lack thereof), but you
have to de-energize the service conductors for such a test. If you
have a maintenance bypass system, that means shutting down power to the
facility. However, it's better to schedule a shutdown than for one to
occur due to conductor failure. Several tests can indicate voltage loss
or current leakage from live service conductors, but only a qualified
person can conduct those tests. These tests cannot replace standard
cable tests (which require de-energization via shutdown or bypass).
- Service disconnects. Infrared will show energy loss at poor
connections. Infrared testing is dangerous, because covers are removed
while the testing is in progress. Only qualified personnel wearing the
appropriate PPE (e.g., blast suits) should perform infrared testing.
- Switchgear. Doing the manufacturer's recommended switchgear
maintenance per the manufacturer's schedule provides energy savings and
reliability. Conduct infrared tests on the connections at buses and
breakers, as well.
- Cables. Small leaks in many cables can add up to
energy losses. This alone justifies cable leakage tests. Serving the
larger purpose of keeping your facility running reliably means you
should include cable leakage tests in a larger cable maintenance
Maintenance for energy efficiency is really a subset of thorough
maintenance for reliability. Review your power supply maintenance
program to ensure it's complete, and you'll have both bases covered.
Once you've eliminated energy losses in your power supply, you can turn
your attention to saving energy in your power distribution system. This
topic will be addressed in the next newsletter.
Your power monitor is set up to show the voltages at
load end of each feeder. Your supply is 484V. You have 10 feeders. All
of them are within 2% of supply voltage, except two -- those are at
448V and 443V. What might be the cause?
The answer to this question appears at the end of this
Transformer replacement offers potential energy
Before ordering a replacement transformer, calculate the total load.
the method appropriate for the type of circuits being supplied
feeder, branch). Then, select the transformer size that most closely
Characterize the load -- is it mostly linear or nonlinear? Would
make sense to split some of this load up and buy two transformers? You
might want to do this if, for example, 20% of the load consists of
resistive heaters and 80% consists of motors.
These are just some of the considerations in proper transformer
selection. Careful selection can turn an equipment failure into energy
NEC at the
You might be surprised if you inspect your bottom-fed
panels. Anytime a raceway enters a switchboard, floor-standing
panelboard, or similar enclosure, it has to allow sufficient space for
NEC-compliant installation of the conductors.
If raceways enter the enclosure below the busbars (or their supports
or other obstructions), they must allow conductor clearance of 8
inches for insulated busbars and 10 inches for uninsulated busbars. In
any case, raceways can't rise more than 3 inches from the bottom of the
Remember the old Maytag repairman commercials? That's
kind of what a confined entry attendant's job is like, most of the
This can lead to some false assumptions.
The attendant may falsely assume that the attendant job involves
doing nothing, or that the work inside the confined space is just
routine. Either assumption can lead to inattention and poor
The person going into the confined space may assume the attendant is
familiar with the permit, but this may not be the case. Always review
the permit with the attendant. Note if extraction gear is required,
monitoring duties the attendant has, and what the communication means
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Electrical Troubleshooting Quiz
First, you'll need to perform voltage drop
Voltage drop is the calculated (not measured) loss due to resistance of
the wire over a distance. If your calculations show excessive voltage
drop (see 215.2(A)(3) FPN No. 2), you need to replace the cables with
larger ones and/or distribute at a higher voltage for a longer
If you have a large difference between the calculations (voltage
drop) and measurements (voltage loss), you have either cable leakage or
a potential across connections. You can use infrared, split cable
or other methods to locate bad cable sections or bad connections. It's
more efficient to test an entire feeder and repair all problems than to
shut down and repair just the worst connections or cable sections. But
time and money may constrain you to do only partial repairs.
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