- -  AGRICULTURE CORE CURRICULUM - - 
 
(CLF2000) Advanced Core Cluster: AGRICULTURAL MECHANICS
 
 (CLF2650) Unit Title: ELECTRICITY

___________________________________________________________________________ 
 (CLF2655) Topic: Electrical Cord Repair        Time     Year(s) 
                                                   2 hours  1 / 2 / 3 / 4
___________________________________________________________________________
 
          Topic Objectives: Upon completion of this lesson, the students
                             will be able to:

          Learning Outcome #:

             (N-6) - Repair an electrical cord.

             (N-7) - Exhibit safe habits when working around electricity.

          Special Material and Equipment: Screwdriver, pocket knife,
                       electrician's pliers, cords, extra plugs

          References: Cooper, E. L. (1987). AGRICULTURAL MECHANICS:
                         FUNDAMENTALS AND APPLICATIONS. Albany, NY: Delmar
                         Publishers.
                       Erpelding, L. H. (1971). AGRIBUSINESS ELECTRICAL 
                         LESSON PLANS. Danville, IL: Interstate Printers & 
                         Publishers.

          Evaluation: Quiz by instructor.

TOPIC PRESENTATION: Electrical Cord Repair

A. Electrical Cord Failure

   1. Causes of Electrical Cord Failure

       a. Electrical cords usually consist of an attachment plug and a
           two- or three-wire insulated conductor.

       b. These wires are made of many fine strands of wire in order to
           make the cord flexible.

       c. If these fine strands of wire are flexed too many times or become
           mechanically damaged, they will eventually break.

       d. The cord's insulation will eventually break down from exposure
           to too much sunlight and heat.
   2. Types of Electrical Cords and their Most Common Damage

       a. Heater Cords 

           1) Heater cords are found on many tools such as branding irons,
               dehorning irons, soldering irons, and space heaters.
 
           2) Intense heat and frequent use are the main causes of heater
               cord failure.

       b. Service Cords

           1) Service cords are found on lamps, power tools, and motors.

           2) Service cord failure is due primarily to being flexed too
               many times or being coiled too tightly around a warm machine.

           3) Most of the damage occurs near the attachment plug or where 
               the cord enters the machine.

       c. Extension Cords

           1) Extension cords are used extensively in agriculture to provide 
               a temporary, flexible extension of an electrical circuit.

           2) Extension cord failure occurs primarily from insulation and
               plug damage. 

B. Repair Procedures

   1. Removing a Plug from a Cord

       a. Remove the cord from the tool or motor and the convenience outlet.

       b. Remove the screws holding the plug together and open the shell
           slowly, observing the position of the wires and terminal clips.

       c. Push the cord protector back over the cord.

       d. Loosen the screws on the terminal clips and remove the wires.

       e. Examine the plug body and terminal clips for damage.

           1) A burned, discolored, broken, or cracked plug body should be
               replaced.

           2) Terminal clips that have lost their spring due to heat should 
               be replaced because they will make poor contact.

   2. Repairing the Cord

       a. Remove all the burned, charred, brittle, or discolored insulation.

           1) Cut the cord back to the point where the insulation of the 
               wires is good.

           2) Make sure that the wires are cut to the same length.

       b. Remove the appropriate amount of outer cord jacket by placing the 
           ends of the wires in the plug channels to determine how much.

       c. Remove the insulation from the individual wire ends just
           enough to hook around the terminal screws. 

       d. Clean the bare wires of any foreign material by scraping and then
           twist the strands together tightly.

   3. Attaching a Plug to a Cord

       a. Tie a holding knot (the Underwriters' knot) in the exposed,
           insulated wires where they extend from the outer cover.

       b. Loop the bare ends of the wires so they may be properly attached 
           to the screw terminal clips.

       c. Wrap the wires around behind the prongs to better withstand pulls 
           on the cord.

       d. Place the looped wire end well under the screw heads and avoid
           fraying when tightening the screws.

       e. Place each screw terminal clip in its proper position in the plug.

       f. Replace the cord protector in the appropriate slot in the plug.

       g. Replace the other half of the plug slowly.

       h. Replace the screws that hold the plug together.

   4. Attaching a Lamp Socket to a Cord

       a. Remove the cap from the socket, usually by pressing at a 
           designated point on the socket and prying.

       b. Insert the end of the cord through the cap and tie the holding 
           knot.

       c. Strip the insulation from the ends of the wires and attach them to 
           the terminal screws without fraying the wires.

       d. Replace the cap onto the socket, making sure that the insulating
           bushing in the top of the cap and the insulation inside the shell 
           are both in good condition and in place.

         ____________________________________________
         ACTIVITY:

         1. Repair a heater or service cord.

         2. Make an extension cord.
         ____________________________________________

6/26/91 OLR/tf

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