Automatic Sectional Cut-out.
Fig. 30.
This cut-out, Fig. 29, is representative of the class which use clockwork, and is both simple and reliable. The house circuit is in series with an electro-magnet which controls a clockwork having a long pinion shaft. This clockwork starts and runs while the house circuit is closed, as on operating a burner, but stops when the circuit is opened and flow of current ceases. The wires leading to different circuits in the building run through a number of contact springs mounted on sliding rods, which have teeth cut on the under side (Fig. 30). These rods have soft iron armatures on the opposite ends from the contact springs, which rest over electro-magnets, also connected to the house circuits. When the clockwork starts, the pinion shaft revolves, but does not engage in any of the sliding rods, as they just clear it. Should a heavy or continuous current pass through one of the electro-magnets, it attracts the armature on the corresponding rod (Fig. 31), and the turning pinion engages in the teeth, drawing up the rod and breaking contact.
Fig. 31.
Fig. 32 is a form of battery protector which works on the gravity principle. Here each section is governed by a rocking contact, operated by two glass bulbs partially filled with a volatile fluid (such as ether), and joined by a glass tube. In one of these bulbs is a platinum wire which is included in the circuit and heats upon the passage of a strong or continuous current. If the circuit is closed too long, the heating of the platinum wire causes the fluid to flow into the upper bulb, and, as the bulbs are pivoted, the increased weight of the upper bulb now overbalances the rocker and breaks the circuit on that section.
Fig. 32.
CHAPTER V.
Lighting of Large Buildings.
The jump spark system is used where it is desired to light clusters of gas jets situated in inaccessible places, or a number of them simultaneously. The spark from a Ruhmkorff coil, being made by a contact broken at the coil and not at the burner, can be divided up among a number of simple burners placed in series. One of the burners used and known as the Smith jump spark burner is shown in Fig. 33. The wires from the coil are attached to the electrodes shown on each side of the burner, and the spark jumps across the gap, situated nearly over the burner orifice. There is a guard-flange of mica round the lower part.
Fig. 34 shows the manner in which the jump spark is applied to a Welsbach burner. A small porcelain clip carrying the spark-gap wires is held on the top of the burner chimney. The electrodes project down into the chimney so that a draught of air cannot carry the stream of gas away from the spark-gap.
Fig. 33., Fig. 34. & Fig. 35
Fig. 35 shows a burner intended for the stage of a theatre, or where the lights are located in dangerous and inaccessible places. The burner is made of porcelain upon which are spun the metal top and bottom. One electrode is also clamped around it, allowing of adjustment and better insulation.
Fig. 36.
These burners are used in series, as shown in Fig. 36. B B B are the burners; S S, the secondary wires from the Ruhmkorff coil, I; P P, the primary coil wires from battery, opened and closed by means of the key, K.
It is often possible to place plain burners close enough so that they can ignite by contagion. In this case one of the plain burners is removed and replaced by a multiple burner, as above.
It is customary to allow sixteen burners to one inch of spark, in which case the spark gaps are adjusted about one-sixteenth of an inch apart. A coil giving a 2-inch spark would operate 32 burners, but actually it would be found preferable to omit a few, so as to make allowance for any slight leak. A spark of over 2 inches is hard to handle, although often used; it is better to make up a number of circuits of, say, 30 burners each, and operate them alternately by a suitable switch.
The wire used to connect the burners is generally bare, although an insulated wire is sometimes used. But the electromotive force of a 2-inch spark is so high that it is better to run the wires so they do not come near anything liable to cause a leak. The remarkable tendency of these high-tension currents must be most carefully guarded against; indeed, it is what makes this style of gas lighting so often unsuccessful. A damp wall, gilt wall-paper, a gas pipe hidden in the plaster, will often lead off the current. The wires should be at least 50 per cent. further off from any object than the spark length; that is, a 2-inch spark circuit should be at least 3 inches away from a wall, and the further the better. It cannot be too strongly urged that every precaution be taken to keep the wires away from objects other than their insulators.
Fig. 37.
Fig. 37 shows the special form of insulator used. It is made of the highest grade glaze filled porcelain, and the screw is passed into it and holds against the lower end as far away from the wire as possible.
Glass tubes should be passed over the wires wherever they come near any metallic object, that is, within sparking distance.