Tom had flash burns to his face. Fortunately, he had been
wearing safety glasses. What was left of his right arm had to
be amputated above the elbow. He was in the hospital for
almost four months. The medical care and physical therapy
would continue for years.
Tom said that he and two experienced linemen were called
out on trouble at two o’clock in the morning. A relatively
new housing development was completely out of telephone
service. Upon arrival at the development, they found a water
company crew up to their waists in a water main break. The
break was at the entrance to the long drive leading back to
the development. The water company excavation was next to the
trench line where the telephone company’s three hundred pair
cable entered the development. The water company crew
indicated it might be twelve hours before they would be done
with their repair. Tom’s foreman assumed that the water main
break or the repair excavation damaged the telephone cable.
Since the nearest termination pedestal on the development side
of the break was almost five hundred feet away, the decision
was made to cut the telephone cable on the development side of
the water problem and splice in a new cable around the water
problem to the source terminal pole on the other side.
The foreman attached the transmitter of a cable tracer to
the telephone cable at the development side pedestal. With a
sensor to pick up the signal, Tom marked the location of the
cable on the ground.
The telephone company maps showed the telephone cable had
been installed in joint trench with the electric and cable TV
cables. Since the NESC® in Rule 353D requires the power
company high voltage cables to be installed at a minimum depth
of 30 inches, the backhoe operator carefully dug down about 24
inches. So as not to damage the other cables, Tom and the
backhoe operator dug the next 6 inches by hand. They found
three jacketed cables: one about 0.9 inches in diameter and
two cables about 1.3 inches in diameter. The cables were only
a few inches apart. One of the larger cables was clearly
marked with a lightning bolt and wording that indicated that
it was a power cable. The NESC® in Rule 350G requires all
direct buried communication cables and jacketed supply cables
installed after January 1, 1996 to be marked with an
identification symbol at spacing not more than 40 inches. The
symbol for power cables is a lightning bolt. The symbol for
communication cables is a telephone hand set. The marking is
only required on one side of the cable.
Since one of the two large cables was marked and the cable
TV cable is usually smaller than the telephone cable, the
unmarked large cable was assumed to be the telephone cable.
Since the transmitter of the cable tracer was still attached
to the telephone cable at the pedestal, they tried to confirm
their assumption. Because the cables were so close together,
the sensor could not confirm their assumption. Tom was
directed to cut the unmarked large cable . . .
Fortunately for Tom, his partners knew CPR and a paramedic
team was only a few minutes away.
The investigation found that the two large cables were both
power cables energized at 7200 Volts. The marking on the cable
Tom cut was on the underside. The fault current that vaporized
Tom’s cable cutter was about 9,000 Amps. The smaller cable
was the cable TV cable. It was marked with a blue stripe
facing to the side. The telephone cable they were looking for
was next to the cable TV cable in undisturbed soil. It was
only marked with the manufacturer’s name.
The NESC® in Rule 352 requires a horizontal minimum
separation of 12 inches between direct buried supply and
communication cables to permit access to and maintenance of
either facility. The cables involved in the accident had been
installed in "Random Separation." "Random
Separation," supply and communication cables buried
together at the same depth with no deliberate separation, is
allowed by the NESC® in Rule 354 but only where the
applicable requirements of Rule 354D are met and all parties
are in agreement. The joint trench agreement between the
telephone and power company did not mention "Random
Separation." The two companies’ construction standards
only showed the NESC® 12-inch minimum. The work orders that
directed the crews to install the cables spoke only of joint
trench. Obviously, the crews who installed the cables were in
agreement. But were the companies in agreement? The cable
tracer equipment could not distinguish between cables
installed so close together. The NESC® in Rule 423E requires
positive identification before cutting into a cable. Did the
people responsible for purchasing the tracer equipment know
about the "random separation"? Had the crews been
properly trained as to the hazards of random separation? Were
the companies in agreement?
Even when the cable is marked, it’s a 50/50 chance that
the marking faces down. If companies are going to do
"Random Separation" to reduce trench expense, the
employees must be properly trained and have the proper tools
to deal with cables in close proximity.
Tom took the power company to court and Tom won. OSHA fined
the telephone company. How much money did the companies really
save going with "Random Separation"?
Test yourself:
Which of the four cables is the three hundred pair
telephone cable?
From left to right, the first cable is a cable TV cable
(diameter 0.93"). The second cable is a 25kV class
high-voltage cable (diameter 1.26"). The third cable is a
15kV class high-voltage cable (diameter 1.10"). The
fourth cable is a 300 pair telephone cable (diameter
1.30").
If you have general questions about the
NESC®, please call
me at 302-454-4910 or e-mail me at dave.young@conectiv.com.
Dave is a consulting engineer with Conectiv Power
Delivery of Wilmington, Delaware, where he has been working with and
teaching all aspects of the NESC for over 33 years. He is a member of
the NESC Interpretations Subcommittee and represents the Edison Electric
Institute on the NESC Overhead Line Clearances Subcommittee 4. Dave is
also an inspector member of the IAEI
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