of the manhole to prevent damage to the cable sheath.
A section of an old tire casing can serve as a protective
boot for this job.
The boards nailed to the two edges of the reel are
called lagging. When the reel is in place, remove the
lagging. You must be careful not to damage the cable
when you pry the lagging loose. Be sure to remove any
projecting nails from the edge of the reel before
starting to remove the cable. Next, you must release the
end of the cable from the reel, and you will then be
ready for the main part of the job.
Assume that the winch line has been drawn into the
duct, as the test line was pulled out. A basket grip is
now attached to the end of the underground cable on
the reel. The end of the basket is secured to the cable
with a tight wrap of tape or wire. A swivel connection
is necessary between the basket and the pulling cable
to relieve twisting of the rope.
If the cable reel is within sight of the winch, it will
take four people, in addition to the winch operator, to
do the job safely. One person attends the reel to see that
the cable rolls off the reel properly. Another in the
manhole guides the cable into the duct. Both inspect
the cable as it unreels and immediately signal stop
pulling when a defect appears so that a closer
inspection can be made for possible damage to the
sheath. A third, stationed in the other manhole at the
pulling end. signals stop pulling when the cable
appears. The fourth crew member, aboveground at the
pulling-end manhole, relays signals to the winch
operator. This procedure enables the winch operator to
concentrate on his job of seeing that the winch line is
wound onto the reel properly.
The speed for pulling cable into a duct varies with
the length of the duct and cable sizes. A single cable
can be pulled in successfully at 75 feet per minute in a
clear. straight duct. When you are handling more than
one cable, reduce the speed to about 20 to 25 feet per
minute, so you can prevent the conductors from
crossing as they enter the duct.
When the stop pulling signal is given, make sure
there is sufficient slack in both manholes for splicing
or terminating the cable. The slack can be adjusted
with the cable basket grip. Exercise care to prevent
injury to the cable insulation. Remove the binding tape
and the basket grip from the cable. The cable is then cut
to the desired length and the cutoff end in the manhole
is sealed unless splicing is done immediately. The end
of the cable remaining on the reel also must be sealed.
In addition, check the seal on the end of the cable that
has traveled through the duct, and reseal it if it has been
broken from the strain.
Gases may be dangerous for several reasons. The
gas concentration may be explosive if it is made up of
methane, sewer gas, natural gas, concentrations of
spilled gasoline, or other liquid fuel vapors. As a
general rule, these gases are heavier than air and will
concentrate in low areas, such as manholes and ducts.
They will remain there until they are dispersed. These
gases are toxic as well as explosive. Other toxic gases
are chlorine, ammonia, and a variety of the sulfide
combinations. Other gases deplete the oxygen in the
manholes and duct systems. Lack of oxygen can be as
deadly as either the explosives or toxic gases. For these
reasons, underground structures must be tested before
workers enter them. Figure 4-49 shows two common
types of test sets used for identifying carbon monoxide
and combustible gases. View A shows a carbon
monoxide tester and view B, an explosimeter. Only
personnel who are specifically trained and certified
may conduct tests for safe entry. Before entering any
underground structures the base confined space
manager or the assistant must certify the area safe for
Test equipment is essential for satisfactory power
system operation. Meters are needed to monitor
system operation conditions and also to check
equipment before and after placing it in service.
Periodic checks are necessary to ensure that the
equipment remains in proper operating condition.
BASIC MEASURING INSTRUMENT
When using measuring instruments, you must
observe certain precautions. For example, it is
especially important to be careful in using an ammeter
because of its low internal resistance. If mistakenly
placed across a voltage source, the meter can be
damaged. Always break the circuit and CONNECT
AN AMMETER IN SERIES with one meter lead going
to each point of the circuit breaker to measure an
unknown quantity. Be sure to de-energize the circuit
before making or breaking the connections.