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

la [Music] the drop wire is an important connecting Link in providing telephone service to our customers whether it's Mrs Collins making that last minute call to the butcher to take care of unexpected guests or it's Susan pry engaged in her favorite Indoor Sport whether it's Charlie Martin over at Centerville trying to get a much needed part for his tractor the grosser taking an order an emergency call for the doctor or a call to the little Factory just out of town the familiar drop wire is usually involved it's the connecting link from the distribution terminal to the customer premises of course the drop wire is only one Link in the chain of outside plant and central office equipment that is necessary to provide service to the customer Dependable service requires not only a trouble-free drop wire but also carefully placed aerial cable well- constructed underground cable and smooth working Dependable equipment in the central office but when a customer needs service none of this plant is of much use if a link in the chain has failed such as this drop wire where it rubs against a tree there are many things that can cause a drop wire to fail as every telephone man knows many of these things are prev able this drop wire was placed across the street without enough clearance a passing truck broke it down this drop wire looks good but it's out of service now a repairman must make a special trip to find the trouble the wire was kinked when it was installed corrosion started where the insulation was damaged and finally the drop failed here's another case where corrosion has shortened the life of the drop wire the sharp Bend at the drop wire clamp cracked the wire covering and corrosion finally put the drop out of service when this drop wire was terminated one of the conductors was nicked movement of the wire resulted in breakage this can be easily repaired but the customer's service was interrupted yes a good drop wire plant is essential to good service Dependable service service that is available day or night the kind of service that people have the right to expect but highquality telephone service requires not only expert workmanship and good judgment by the installer or repairman it also requires materials and tools and methods that experience is shown to be the safest the best and easiest to use throughout the Bell System everywhere telephone people are continually searching for even better ways here at the Bell Telephone Laboratories no stone is left unturned it's a search that never stops in this room at the Laboratories experiments are conducted to develop improved rubber compounds it was here that the neoprene compound was developed for jacketing the wire that we commonly call NP drop wire yes we were looking for a more durable covering for distribution wire than the former weatherproof cotton braid we found an answer to this problem in neoprene one of the synthetic rubbers the jacket compound is made of neoprene and 10 other ingredients neoprene is a synthetic rubber which was chosen for its resistance to sunlight and weathering believe it or not it's made of coal Limestone and salt combined with other ingredients it acquires the properties that make it appliable yet durable covering carbon black gives it toughness and resistance to abrasion this ingredient an antioxidant with a long name is also called nezone D it improves resistance to deterioration some ingredients such as clay and paraffin are included as manufacturing AIDS although these also help to maintain a balance in physical characteristics the others while used in smaller quantity are just as important in the final product NP drop wire consists of two parallel conductors of the same material and size is TP wire we've made the insulation somewhat thicker it is formed around the wires in two adjacent d-shaped sections joined on the flat side by a thin fin of insulation next comes an inner covering which also acts as a reinforcement this also makes it easier to remove the jacket from the conductor insulation over this covering is a heavy jacket of neoprene and these two small parallel ridges along one edge of the wire are used to distinguish the tip and ring conductors however this new wire was not released from manufacturer until it had passed many exhaustive tests these tests are the same as the ones applied to NP drop wire before it is shipped from Western Electric this machine measures the pressure required to crush the insulation the insulated conductor is placed between two steel Anvil and pressure applied until the insulation crushes as the test proceeds both the applied load and the thickness of the sample are recorded on a chart when the insulation crushes it is indicated by a sharp drop of the pen on the chart there high resistance to compression means that the wire will not be damaged where it is squeezed by clamps and other attachments in order that the wire May withstand the loads applied at attachments the insulation must adhere tightly to the conductor this machine determines the force required to strip a short length of insulation from the conductor much as this insulation is stripped from Wire by pliers now over here a piece of wire held by the standard drop wire clamps is being pulled to its braking strength this tests both the strength of the wire and the ability of the clamps to hold the wire firmly this machine is like the ones used by Western Electric to test the insulation on all completed wire if a defect in the insulation passes through the machine 9,000 volts Flash from the chain bead electrode through which the wire passes to the grounded conductors burning a hole in the insulation and automatically stopping the Reel winding up the wire the wire is then cut and the bad piece removed another thing that we want to know is how the insulation and jacket of the wire will resist crushing over a long period of time in this oxygen bomb lengths of in insulated wire are suspended in pure oxygen at a temperature of 158° F and under a pressure of 300 lb for as long as 10 days one day of such treatment is more severe in its aging effect on the insulation than one year outdoors in the hot sun after this accelerated aging the samples are tested and results compared with results shown by samples before aging but even this is not enough at Chester New Jersey NP drop wire is tested under conditions similar to or worse than those expected under normal usage in this dense Thicket of birch trees are strung 44 samples of wire some are experimental others are samples of regular production wire day after day these wires are subjected to severe abrasion as the trees move in the wind how were the wires strung through this dense growth they were shot through with a line gun developed by the engineer at the the field Laboratory