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.
106. The apparatus used in electric gas lighting, on the parallel system, consists of a battery of about six cells, of a type giving a strong current, such as the Fuller Mercury Bichromate battery, and of a spark coil connected in series with it. The spark coil has a single circuit of fine wire, and its action is to produce a spark by self-induction on opening its circuit, when used in connection with the battery. The arrangement of the apparatus is shown in Fig. 84, where k is the spark coil, connected at one side to the gas pipe p, and at the other side to the first cell of the series c, c, etc. From the last cell a well insulated wire is carried up to the gas bracket b, and connected to the tip as already described, the circuit to ground being completed through the sliding contact lever a. In applying the gas-lighting system to chandeliers, the wire is run in the space between the gas pipe and outer tube, and great care must be exercised in insulating at all points where sharp metal edges are passed, as the E. M. F. used is very high. Gas brackets usually have but a single pipe, and the wire should be run on the lower side, being tied on with thread and shellaced. When the shellac is dry, the thread may be removed, and the wire will adhere to the metal. A short helix should be made wherever there is a joint, to prevent the wire from breaking as a result of frequent turning of the bracket. The wire used for this part of the construction is No. 20 or 22 B. & S. gauge, well insulated, and colored to suit the bracket. For the house circuits, No. 14 or 16 wire should be used.
107. A diagrammatic arrangement of gas-lighting apparatus is shown in Fig. 85, indicating the method of connection of the automatic and pendant burners. The spark coil s is grounded at G, and connected to the battery B at the other terminal. The battery wire b runs the full length of the circuit, branches being taken to the pendants p, p, and double wires to the automatic a, the battery wire connecting with both buttons of the double push button c.
108. Since the battery is momentarily short circuited every time a spark is obtained, it would soon run down if the contacts on the burner were to remain permanently touching. To give notice of this, a relay (Fig. 86) may be used in series with the battery, the current entering at b and passing out at c, after circulating around the coil. The magnetic circuit is completed by an armature a, which is held back against a stop by the weight w when no current is passing. If a short circuit occurs, the armature is attracted, and the spring d is pressed against the platinum-tipped screw s, completing a local circuit, by means of the wires e, f, through a vibrating bell and one-cell battery. The current used in lighting the gas at a burner is of such short duration that the bell is not rung. A modification of this arrangement is to provide an armature on the spark coil itself, which shall close a local alarm circuit when the battery is short circuited.