Electric switch

“ The electric light company will supply a sufficiently large wire from transformer to switch; the firm does the remainder of the wiring.
FEEDERS. From this large double-pole switch (which is the main cut-off) radiate “feeder” wires to the various parts of the building, to supply the lamp circuits. These feeders have to be carefully gauged according to the number of lamps, or rather, amperes, they are required to carry, in order to avoid resistance in the wire; or in other words, must not crowd the carrying capacity of the wire, or the resistance will make the wire hot and might cause fire. ”

“ A switch is a piece of apparatus for making, breaking, or changing the connections in an electric circuit.
The particular form and construction of any switch is governed by the electrical conditions under which it must operate.
Since the electric current cannot be stopped instantly when the circuit in which it is flowing, is broken, an arc is formed as the switch contacts separate; this tends to burn the contacts, and to short circuit, the severity of such action depending on the voltage and the proximity of the switch terminals. ”

“ In the matter of switches, controlling apparatus, and switchboards, an alternating transmission requires much more equipment than a system using continuous, constant current. The ten dynamos in the generating station at St. Maurice, with a capacity of 3,450 kilowatts at 23,000 volts, are each connected and disconnected with the transmission by a switch in a small circular column of cast-iron that stands hardly breast high. ”

“ Where generators operate at the maximum voltage of the system only two main groups of switches are necessary, one group connecting generators to bus-bars, and the other group connecting bus-bars to the transmission lines. As soon as step-up transformers are introduced the number of switch groups must be increased to four if the usual method of connection is followed, and there must be both a high voltage and a low voltage set of bus-bars. ”

“ Great powers as well as very high voltages not only increase the element of personal danger to an attendant who must stand close to a switch while operating it, but also render the damage to other apparatus that may result from any failure of or short-circuit in a switch much more serious. ”

“ But the electric-light men also had the advantage of the experience gained by telephone men in building local circuits. It is written that the first electric-light switching devices were derived from the telegraph switch, only enlarged to accommodate the greater volume of current. The strap key, the telegraph key and the switchboard plug were all utilized in central-station electric lighting, and the arc that formed between the terminals following the withdrawal of the plugs was usually blown out with the breath, or whipped out with a cloth, or extinguished with a handful of sand. ”

“ Should the current become too great for its carrying capacity, the alloy would melt and fall down upon the non-conducting base upon which the several portions of the switch are mounted, thus breaking the circuit and cutting off the current until suitable provision be made for its control, when another safety-catch is substituted for the melted one, and all is ready for continued operation. When wires are led into houses, a different form of safety-catch is used. ”

“ In other instances they are formed solely through switch contacts. In all cases the control, when from a distance, is received upon relays suitable for being controlled by the small currents which are adapted to flow over long lines. In all instances the power for moving a brush is derived from the main shaft and only the control of the movement is derived from electromagnets, relays, or other electric sources. In many instances the clutch circuit is closed through contacts of its own switch and, therefore, may be closed only when its switch is in some predetermined position. ”

“ The switch is merely a device to open and close the path of electricity.
The socket is the termination of two wires from the generator or battery, into which the bulb of the light is put and other connections made.
You will notice two wires on every electric connection. This is to make a complete electric circuit (path) to and from the points where it is used.
The outlet is the opening where the socket can be placed. The more outlets you have in your home before building the better off you will be forever and ever. ”

“ Fig. 2,274.—General Electric circuit closing auxiliary switch. This switch closes when the circuit breaker opens, and may be used to announce the automatic opening of the circuit breaker through the means of an indicating lamp or an alarm bell. It is often necessary to arrange one circuit breaker so that, in opening, it will trip others. This may be accomplished by using a circuit closing auxiliary switch in connection with a low voltage or shunt trip attachment on the circuit breakers to be tripped. ”

“ An electrical alarm and a pile, located near the switch lever. As long as one of the two plates of the switch is applied against the rail, one of the two commutators is inclined and no current passes. A space of one millimeter is sufficient to bring the commutator to a horizontal position and to cause the electric alarm to ring continuously. If the apparatus gets out of order, it is known at once ”

“ Compared with those of the open-air type, oil switches effect a great saving of space, develop no exposed arcs or metallic vapors, cause little if any oscillation or rise of voltage in an alternating circuit, and can be depended on to open circuits of any voltage and capacity now in use. In the tests above mentioned at Kalamazoo, a three-phase oil switch making two breaks in each phase and with all the six contacts in a single oil-bath was used to open circuits of 25,000 volts and 1,200 to 1,300 kilovolt-arcs with satisfactory results. ”

“ The wire from the secondary of the coil is run to the switch-handle, H, great care being taken that it does not pass near to the circuit wires, or contact points. Revolving the switch-handle connects the secondary wire to each circuit in turn. It will be noticed that, unlike a battery switch, this one has a large base, long switch-arm, contact points situated far apart, and every precaution taken to control the passage of the high-tension current. The base should always be of rubber or glass. Shellacked-wood, or such substitutes, are productive of trouble.
Fig. ”

“ After drilling, remove the valve, take off the burr with a piece of emery paper and replace ready for work.
Easy Experiments with Electric-Light Circuit
Arc-Light Motor and Water Rheostat
An electric-light circuit will be found much less expensive than batteries for performing electrical experiments. The sketch shows how a small arc light and motor may be connected to the light socket, A. The light is removed and a plug with wire connections is put in its place. One wire runs to the switch, B, and the other connects with the water rheostat, which is used for reducing the current. ”

“ The electrically operated switches may be of the open type, mounted on a slate or marble switchboard, when the whole control outfit is placed in a room which is comparatively free from dust or dirt of any kind, and where there is no danger of employees coming in contact with the switches. The other type of switch is entirely enclosed, the main contacts being oil immersed. ”

“ Every alternator switch, every selector switch, every group switch, and every feeder switch upon the main floor is here represented by a small switch. The small switch is connected into a control circuit which receives its supply of energy at 110 volts from a small motor generator set and storage battery. ”

“ Since dirt or oxidation would prevent good contact under a simple pressure between the contact surfaces, the mechanism of a switch provides a sliding contact.
In the general design of switches, all parts which carry current are given a cross sectional area of at least one square inch per 1,000 amperes if they be made of copper, and about three times as much if made of brass, as the conductivity of the latter is only one-third that of the former. Furthermore, the current should never be permitted to pass through springs, as the heat generated will destroy their elasticity. ”

“ Why can a bird sit on a live wire without getting a shock, while a man would get a shock if he reached up and took hold of the same wire?
We have just been laying emphasis on the fact that for electricity to flow out of a dynamo or battery, it must have a complete circuit back to the battery or dynamo. Yet only one wire is needed in order to telegraph between two stations. Likewise, a single wire could be made to carry into a building the current for electric lights. This is because the ground can carry electricity. ”

“ It’s just an ordinary electric circuit-breaker, the same as they use on street-cars, and it is buried in oil to keep it from arcing—as all switches are when they’re under voltages as high as ours will be. ”

“ How quickly a spoon inserted into a hot cup of tea becomes uncomfortably hot, though the hand can be held very close to the liquid without feeling more than a gentle warmth. And we all have noticed that the very least air-gap in an electric circuit effectively breaks a current capable of traversing miles of wire. If the current is so intense that it insists on passing the gap, it leaps across with a report, making a spark that is at once intensely bright and hot. Metal wires are to electricity what speaking tubes are to sound; they are as it were electrical tubes through the air and ether. ”

“ The function of a circuit closing relay is to close an electrical circuit, usually direct current, through a trip coil on an oil switch or circuit breaker, or it may short circuit a low voltage release coil, and thereby open the oil switch or circuit breaker on occurrence of the condition upon which the relay is designed to operate. Direct current at 125 or 250 volts taken from exciter bus bars or storage battery system is generally used for the tripping circuit. ”

“ D is piece of copper running one-third of the way around, and comes in contact with another brush, E. Then fasten a small piece of wire from C to D that carries the current to No. 2, while E is on copper. The other feed wire is direct from main circuit to window. F is pulley wheel running to reducer. No. 3 is fuse blocks, which can be used and are much safer than without. This switch cost me twenty-five cents. Of course, I am my own electrician. It will cost no more to any one, as it is very simple. ”

“ The electricity corresponds to the water. Your dynamo pushes the electricity around and around the circuit, as the paddle pushes the water. But let some one break the circuit by putting a partition between two parts of it, and the electricity immediately stops flowing. One of the most effective partitions we can put into an electric circuit is a gap of air. It is very difficult for any electricity to flow through the air; so if we simply cut the wire in two, electricity can no longer flow from one part to the other, and the current is broken. ”

“ High wiring is carried entirely on the roof of the car where it is entirely out of the way and where the operator cannot come in contact with it. The switchboard should be of the utmost simplicity. Usually the negative and equalizer switches, and the field break-up switch are mounted on the frame of the converter. The double throw switch for starting and running the converter can be mounted under the floor of the car and operated by handle at the switchboard. The rheostat can be mounted back of the switchboard on brackets bolted to the car super-structure. ”

“ This is particularly true in cases where energy transmitted over a single circuit is distributed for both incandescent lamps and large electric motors, because the starting and operation of such motors causes large fluctuations of amperes and terminal voltage on the transmission circuits. To hold such fluctuations within limits which a sub-station can readily compensate for, it is necessary that the loss in the transmission line be moderate, say often within ten per cent of the total voltage delivered to it at maximum load. ”

“ It is, in fact, common practice in central stations to judge the voltage of the new dynamo merely by the appearance of its pilot lamp.
Ques. How is a machine cut out of the circuit?
Ans. When shutting down a machine, the load or current must first be reduced, by gradually closing the stop valve of the engine, or inserting resistance into the shunt circuit by means of the hand regulator; then when the ammeter indicates nine or ten amperes, the main switch is opened, and the engine stopped. ”

“ If close regulation of the direct-current voltage is not demanded the converter field can be used more freely. As a matter of fact the synchronous converter finds its chief use in electric traction where close regulation is not important, and motor-generators in one form or another have been found more suitable for electric-lighting work. ”

“ There is no fundamental objection to operating make and break bells on electric light circuits. Providing the voltage and amperage are the same, there is little difference between the current from a direct-current dynamo and that from a battery. But owing to the higher voltages of the lighting circuit over that generally employed from batteries, the bell coils must be wound to high resistances to keep down the current strength. ”