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. CABLE  INSTALLATION 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. DANGEROUS GASES 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 entry. MAINTENANCE 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 PRECAUTIONS 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. 4-33