Your facility may use large furnaces, tanks, or other
confined entry vessels for various processes. Most of the maintenance
work -- cleaning surfaces, checking welds, replacing hooks, liners,
tiles -- belongs to mechanics, not electricians.
Yet, electricians must provide temporary power, ventilation, and
light. The typical practice is to string portable cord along the entry
structure (e.g., stairway or ladder), and into the vessel. This creates
tripping and (possible) shock hazards, and exposes the cords to being
walked on, spilled on, or punctured.
This approach may seem like the only option, because operating
conditions make permanent wiring or additional penetrations for plugs
unacceptable. But it isn't. For example, you can:
Each of these options requires a small investment, but the increased
safety and improved productivity usually justify that. Ask your
electrical supplier about products that may suit your application.
- Add brackets along a predetermined path, to hang cords out of the
way. Apply covers (e.g., cut tennis balls) when not in use for
- Install mesh cable tray (removable or permanent) for the
- Temporarily install surface-mounted raceway.
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At the operator console, the graphic for a large tank
shows 70% full, then suddenly drops to empty (triggering a process
interruption). A second later, it briefly goes to 100% full (triggering
high-level alarms), and then goes back to 70%. It stays there for some
time, then repeats this erratic operation. What should you do to
eliminate this problem?
The answer to this question appears at the end of this
Vessels (and similar equipment) often contain
that should be replaced or calibrated whenever the vessel is out of
service (e.g., for repair). This work is often incidental to the reason
for the downtime, and it must be done on a tight schedule because each
hour of downtime means lost revenue and possibly lost customers.
Complicating matters, work inside a vessel is typically cramped, hot,
For example, the mechanics must replace tiles in an annealing
furnace, after waiting through five days of downtime for the interior
air to cool to 150°F. Standing in a fan-blown breeze, they work in
30-minute shifts. When the project is done, the three-day heat-up
process will start.
Your crew has to do more than supply power for fans and lights. Now
is the time to replace the dozen process sensors variously located
throughout the first and last chambers of the furnace (rather than wait
for one to fail three months later). You don't want techs going back
forth for parts and tools, or using up "inside time" to open packaging,
strip wires, or tape threads. Nor do you want them crawling in and out
to perform the requisite testing.
Different crews working in the area will slow each other down, yet
all work must be concurrent with that of the mechanics. You must work
"between the work."
To succeed, plan the job. Then do a mockup, and rehearse several
times. You don't need to duplicate the actual vessel; you just need to
identify the steps and what's needed to perform each one. A mockup can
consist of a few tables set up in the parking lot.
Consider having a dedicated support crew (cannot include the vessel
attendant) outside the vessel, even if they spend most of their time
standing around. Do these practice sessions, and the "low utilization"
support crew, seem like excessive uses of labor? Ask your plant manager
how much revenue the plant loses every hour that vessel is out of
service. The answer may quickly justify any labor cost concerns. But
don't throw people at the job; plan the job for fastest execution and
staff it accordingly.
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NEC at the Facility
When using the ampacity tables (Tables 310.16 -- 21)
remember to apply the adjustment factors [310.15(B)2]. These differ
the correction factors that appear at the bottom of Tables
-- 20 (Table 21 does not have correction factors).
A common misperception is that OSHA bases fines only on
physical safety violations. Recognizing that most workplace injuries
result from unsafe acts (vs. unsafe conditions), OSHA also examines
safety training and hazard communication systems. It's better that you
examine these before OSHA does. Correcting deficiencies can reduce or
eliminate post-incident fines -- or even prevent an incident in the
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Answer to Electrical
Erratic indications of process variables may result
loose connections -- so check screw terminals and crimped
If the problem remains, suspect electromagnetic interference (EMI)
radio frequency interference (RFI). You may be able to capture an RFI
event using a recording DMM or power analyzer. Look for any source of
RFI -- such as fixed or portable wireless equipment -- especially
near the sensor wiring, the I/O rack, or the control console.
A common source of EMI is a voltage induced from 480V or 120V wiring
running parallel to the wiring between the sensor and the transmitter
(other likely places are around the I/O rack and around the operator
station). The transmitter sees the induced voltage in addition to the
input from the sensor as though they are one big input signal. The
resulting 4 mA to 20 mA output signal is artificially large.
If specific equipment switches on (or off), coincident to the
appearance of the anomaly, wiring for the equipment is probably your
Having trouble finding that EMI source? You may need to lift wires
via the "divide and conquer" method. First, determine the timing of the
anomalies, so you can plan downtime around when one is likely to occur.
Coordinate with the operators to determine how long you'll have.
Identify the affected transmitter, and verify against the loop
diagram. Shortly before an anomaly is due to occur, break the loop at
the transmitter and place a recording DMM on each side. Suppose you saw
no anomaly on one side, but you saw a spike on the other. Now you know
the direction in which to continue troubleshooting.
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Show & Events
Visit the 2006 EC&M E-TradeShow, a
Virtual Business Event
Don't miss these scheduled seminars on October 18 in the EC&M
Before attending these events, make sure you visit the 2006 EC&M
e-TradeShow, a year-long virtual business event. In addition to
attending live activities at conference sessions scheduled throughout
the year, you can meet with exhibitors in virtual exhibit halls. You
also access past presentations that are archived in the e-TradeShow.
Employing the latest interactive 3D technology, sponsors use online
trade-show booths to generate leads on a continuous basis throughout
year, while interacting live with customers and prospects during
scheduled events. Free access and all the information you need are
available at the event's Web
- "The Basics of Insulation Resistance Testing," by John Olobri, Dir.
Sales and Marketing, AEMC Instruments (9:00 am EST and PST, Conference
- "Good Project Management, Enhancing the Bottom Line," by John
Senior Director, Editorial and EC&M Development (11:00 am EST
Conference Room A)
- "Presenting AEMC's 3-Phase PQ Analyzer," by Ed Cunie, Eastern
Regional Manager, AEMC Instruments (10:00 am EST and PST, Conference
- "Electrical Market News Update," by Jim Lucy, Chief Editor,
Electrical Wholesaling, and Dale Funk, Chief Editor,
Marketing (10:00 am EST and PST, Conference Room B)
Maryland Facilities Expo
Held October 25-26 at The Fairgrounds in Timonium, Md.,
the Maryland Facilities Expo is a free two-day trade show, offering an
exhibition of products and services along with educational seminars for
facilities personnel working in all types of industries, including
commercial, industrial, educational, government, health care, hotel and
resort, distribution, and warehousing.
A few sessions in the conference track that may be of particular
interest to EC&M readers include: "The Top 10 Cited OSHA
Standards," presented by Eddie Bell, Chesapeake Region Safety Council
and "Standby Power Generators -- What You Need to Know," by Al Grimes,
Curtis Engine and Equipment, Inc.
For more information on this show, visit the event's Web
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