Fig. 990.—Bottom of General Electric manhole junction box; view from manhole interior. The cables enter the bottom of the box as shown through composition nozzles to which the lead sheathes are united by a wiped solder connection, forming a permanent water and gas tight joint. Stuffing boxes are sometimes substituted, doing away with the wiped joint, rendering the boxes suitable for use with unleaded or braided cables. The normal position of the distributing cables is in the upper ducts so that they may be brought to the junction box without crossing other lines. The entrance nozzles and seats are so arranged that all terminals are soldered to cables outside of box and any cable may be removed without disturbing any soldered joint. The wiped joints unite electrically the lead sheathes of all cables entering the box and by connecting a single earth bond to the shell of the box all cable sheathes are solidly grounded. Incombustible shields prevent the arc from a blown fuse making a ground connection to the shell or inner cover.
Ques. How are pot heads made?
Ans. They are usually made in three parts, the base being of cast brass, having a diameter depending upon the size of the conductors, with a hole in the lower end threaded within in such a manner as to make a tight fit on the cable.
Ques. How is a pot head connected to a cable?
Ans. After the cable has been bent in to the proper position, the brass base is slipped down over it with the larger end up, and then screwed down on the lead sheath. The threads cut down into the lead sheath to a distance of about ½ inch along the sheath, thus making an air tight connection without necessitating the making of a wiped joint.
The separate conductors are now bared of their insulation for a distance of about two inches, and then spliced to heavy rubber covered braided wire of sufficient length to reach the primary service boxes. The joints connecting these rubber covered wires and the cable conductors are spliced in the same manner as straight splices, the paper sleeves used being of sufficient diameter to be backed out of the way over the rubber insulation. When the splice is completed a brass shell threaded at one end to fit a female thread in the upper end of the brass base, is slipped over the end of the rubber covered wire and screwed into the base. A hood of sheet copper having the form of a quarter section of a ball is slipped over the top of the frame and its lower edge tracked in position below the horizontal shelf. This hood makes the pot head water, snow, and insect proof.
CHAPTER XLI
WIRING OF BUILDINGS
In laying out the circuits for a dwelling house, the cut out cabinets should be located first. In many houses only one cut out cabinet is necessary, but in large houses it is convenient to have one on each floor, with vertical mains running through them from the top to the bottom of the house.