Bell System Film - Drop Wire Runs Part 1 (b)

yes the neoprene jacket is tough and NP wire will give better service than any drop wire that has been available so far provided it is properly installed that's a challenge to good workmanship and good workmanship doesn't just happen it's the result of careful attention to small details and particular attention at those points where trouble is most likely to occur Studies have dropped wire failures show that more than a third were preventable and that about 82% of these preventable troubles occurred in three general areas injury to the wire at dead end detachments accounted for 7% of preventable troubles abrasion at the pole or along the lead between poles accounted for 25% where caused by the wire rubbing against trees 50% there are various ways ways of preventing abrasion by trees such as trimming or placing wire guards but the best way is to select a route where there will be the least possible chance of contact with buildings or future tree growth it's in this selection of root that judgment plays an important part in providing good service now let's look at drop wire failures due to damage at attachments the greater toughness of the covering of the neoprene wire should help to decrease these troubl but the neoprene jacket can't do the job alone careful workmanship has a lot to do with it for example one safeguard against damage is to provide slack wire at the building in a smooth curve a sharp Bend in The Wire sooner or later is almost certain to result in cracking of the wire covering therefore avoid sharp bends and be careful to avoid Kinks when paying out the drop wire another source of drop wire trouble is breakage and other damage caused by excess tension this tight drop is actually pulling the cable out of line make sure that every drop wire is given at least the required amount of sag that's one of the most important things we can do to increase the service life of the wire minimum sages for spans of various lengths have been specified to avoid excess tension let's watch a demonst rtion that shows very clearly how sag affects tension in drop wires here a length of NP wire has been suspended 5 ft above the ground between two points 100 ft apart a scale has been placed at one end to show the tension existing in the drop the specified minimum sag for a 100 ft drop from po to building is 2 ft under these conditions the scale shows a tension of 27 lb but now let's reduce the SAG to 1T which is 1/2 the required minimum and see what happens the tension has increased to 54 lb twice the amount it was before now leaving the SAG at 1 ft let's add weights totaling 22 lb this is about the weight that would be added by a 1/4 in coating of ice the tension in the drop wire has now increased to 135 lb however if we lower the drop to 2 ft which is the minimum sag specified in the practices the tension with the additional 22 lb of ice is reduced to 100 lb now let's go a step farther what will happen to the tension if we increase the SAG from the 2T minimum and make it 3 ft the scale now shows a tension of only 74 lb and remember we still have that 22 pounds of ice on the wire so you see the amount of sag that we put in a drop wire varies its tension over a wide range that's why it's always a good practice to provide more sag than the minimum required Whenever there are no clearance problems that extra sag is good insurance against drop wire failure of course no two drop wire jobs are exactly alike slightly different situations call for the Contin continual use of good judgment by the installer and repairman but this good judgment plus highquality materials and tools and methods outlined in system practices plus good workmanship and careful attention to details are all that's needed to meet any combination of conditions remember the trouble spots make a careful survey to select a route that will avoid interference from trees buildings and foreign objects Place drop wire clamps properly provide slack in the form of a smooth curve avoid Kinks when paying out the wire if paid out by hand any tendency to Kink can be avoided by occasionally reversing the coil provide at least the minimum required sag and more if possible avoid chances for damage at the pole avoid Nicks in the conductors bring the outer covering to the proper Point within the terminal to protect the insulation and extend the insulation to the required distance from the washer to prevent crosses or short circuits observe Good Housekeeping these things will help us cut down many of the troubles that result in more than a third of all drop wire failures attention to the trouble spots will help us build drop wires that will be a strong Link in the chain of equipment and outside plant that makes possible Dependable telephone service to our customers [Music]