This section is from the book "A Treatise On Architecture And Building Construction Vol3: Stair Building, Ornamental Ironwork, Roofing, Sheet-Metal Work, Electric-Light Wiring And Bellwork", by The Colliery Engineer Co.. Also available from Amazon: A Treatise On Architecture And Building Construction.
49. There are three methods of running electric-light wires, namely, cleat work, molding, and concealed work. Cleat work is used in such places where appearance is of little consequence, as in factories, and is the least expensive method of running wires. Cleats are narrow strips of wood placed at regular intervals along the wall or ceiling, arranged to hold the wires in position, clear of each other and of neighboring objects. Such a cleat is shown in Fig. 37. It is made in two pieces, the lower a being a flat strip 1/2 inch or more in thickness by about 1 inch in width and 4 inches long; the cap b has grooves across its lower surface to receive the wires, which must be separated at least 2 1/2 inches to conform to the requirements of the insurance companies. The cleat is secured to its support by means of screws passing through the holes s, s. Screw cleats, such as that illustrated in Fig. 38, may be used if desired. In this style of insulator, a porcelain split bushing b is put over the wire and supported by a metal clamp in two pieces c and d, held together by a screw s. A wooden bushing is sometimes substituted for the porcelain, but does not provide as reliable insulation.
50. When a wire crosses another, and there is the full E. M. F. of the circuit between them, extra insulation is required, and a wrapping of rubber tape may be laid on, as indicated in Fig. 39 at a and b. The cleats c and d have three notches in them to receive the three main leads, and are correspondingly larger than the two-wire cleats.
51. When the wires are to pass through a wall or partition or wooden beams, they must be protected by insulating tubes of glass or porcelain, or some substance that will not burn, and so constructed that they will not pull out of place. Such a tube is shown in Fig. 40; the thread on the body b enables the insulator to be screwed firmly into place by means of the hexagonal head h, which has a shoulder like a bolt head, and may be set up tightly.
52. When the house-service wires are brought into the building direct from an overhead line, wall insulators of the type of Fig. 41 should be used. It will be noticed that the outer end projects downwards, and the bend thus given to the wire, called a drip loop, will cause the rain to fall off at a, which would otherwise creep along the wire into the house.
53. In breweries, dye houses, etc., the wires, being subject to dampness, must be separated at least 6 inches, and waterproof keyless sockets should be used for the lamps. In paper mills, sawmills, etc., which present extra fire risks, no switches should be used. The smallest size of wire allowed for cleat work is No. 12 B. & S.
54. Molded work is a style of wiring more ornamental than cleat work, and is generally used in houses in which no provision has been made for accommodation of the wires at the time of building. The molding is made of pine cut into lengths of about 10 feet, and consists of two parts, one of which b, Fig. 42, is called the base or mold, and is provided with longitudinal grooves to hold the wires, and the other part c is called the capping, which is intended to hold the wires in place and present a finished exterior. For this reason the capping is usually ornamented to correspond with the decoration of the room. The base is screwed in position first, being held by the flat-head screws s, s, and the capping is then fitted over and secured by round-head brass screws s'; iron screws would not look well. Particular care should be taken that these screws do not touch the wires or damage the insulation, as a fault might thereby develop which would cause trouble or even fire risk. The wires, if positive and negative, should be separated a distance of at least 1/2 inch from each other. Molding must not be used in places where there is dampness, and should in every case have at least two coats of some waterproof paint, or be otherwise treated so as to be impervious to moisture.
55. It is usually desirable to have molding arranged so as to be unnoticeable. It may frequently be set as a border to the wall paper, or used instead of picture molding, the hooks being attached in the ordinary manner over the edge of the capping. (See Fig. 43.) When molding is required at only one side of a room, and an unsymmetrical appearance is to be avoided, dummy molding, carrying no wires, may be employed to produce the desired effect.