CHAPTER VI.

ELECTRIC LIGHT AND POWER INSTALLATIONS.

In order to fully understand the hazards and purposes of various protective devices for electric installations some knowledge of the different appliances and connections is necessary.

Electricity used commercially is produced by mechanical means and hazards are inherent in all stages of production, transmission and use, hence every point from the generator to the lamp or motor needs attention, and should at all times be kept in perfect condition. Vibration, insecure fastenings, deterioration from wear and tear, carelessness in handling and in oversight and many other causes contribute to the hazards as much as an originally poor installation; the system needs care and attention at all times, and every point needing repairs should receive them as soon as the need is found. Procrastination here is the thief of the insurance company.

All the rulings of this chapter are in conformity with the 1901 "NATIONAL ELECTRIC CODE,” RULES AND REQUIREMENTS of the National Board of Fire Underwriters for the installation of electric wiring and apparatus, as recommended by the Underwriters' National Electric Association. Edition of 1901.

GENERATORS AND DYNAMOS.-These machines are made for generating or producing electric currents, are propelled by some separate mechanical power, and are composed of the following parts:

Field Magnets.-Electro-magnets composed of soft iron bars, or bundles of iron, or solid iron castings around which insulated wire is closely wound; being electro-magnets, they are only polarized while currents of electricity are passing through them, and while some of them hold sufficient magnetism to produce a current as soon as the dynamo is started, others need an "exciter," and in some cases, another dynamo is used to produce the initial magnetism, as it is necessary that the magnets be in a state of

magnetism before a current can be produced. Dynamos are either of one magnet, North and South pole, or multipolar, consisting of a number of magnet poles, generally on a circular shaped field magnet radiating toward the center.

Armature. This is made of mass or piece of iron or steel, on a collection of pieces of iron or wire carrying independent coils of insulated wire in sections, and is between the field magnets. The space between the field magnets and the armature is called the field, and it is by the rotation or motion of the armature in this field, or by the field magnets rotating about the armature that the electric current is produced.

Commutator.-The ends of the wire from each section of the armature are run to one end of the armature shaft (the wires being thoroughly insulated from each other, from every other wire and from the shaft), and are here connected to a copper cylinder or a series of copper strips in sections, with alternating sections of non-conducting material between, this copper section being the commutator.

Brushes. Resting upon the commutator are the brushes; these are of different forms but usually of copper (a bundle of strips, layers of woven netting, wires in bundles, etc.); carbon rods or slabs are also used.

The current is produced by the rotation of the armature in the field, or the rotation of the field magnets, about the armature, and is led off through the armature to the commutator and here taken up by the brushes to be carried thence by the conductors to the outside lines. The currents generated are of two kinds, i. e., alternating, reversed, or periodic where the current alternately flows in opposite directions and in which the potential is high, usually from 1,000 to 10,000 volts, and direct or constant in which the potential is high or low, but the current flows invariably in one direction. Certain types of alternating currents, in which the currents flowing in opposite directions, constantly differ from each other by a constant proportion of periods of alternation, produced by the method of winding the armature, are called polyphase, multiphase or rotary currents.

Location and Hazards.—As moisture tends to cause a degeneration in the insulation of the wires and so allow a leakage of current which is liable to produce such overheating as to seriously

damage the dynamo, it is necessary that the location be dry, and that a waterproof cover be kept on the dynamo when not running, in order to prevent moisture falling on it; the cover also tends to keep any flying inflammable materials from collecting on the dynamo. In order to prevent any liability of a ground occurring and presenting the possibility of the armature burning out from the heat produced, the dynamo should be thoroughly insulated from earth, walls, floors and all metallic substances and set on a wooden base frame filled to prevent absorption of moisture; the base frame must be kept clean, dry and free from oil and metal dust, as these tend to form a line of conductivity for the current. There is always more or less of a tendency to spark, i. e., to produce sparks, in a dynamo, and as the sparks frequently have a sufficient intensity of heat to produce combustion, it becomes particularly necessary to locate the dynamo in some room wherein no hazardous process is carried on nor where there is any liability to be any inflammable gases or flying combustible material.

Every constant-potential generator must be protected from excessive current by a safety fuse, or equivalent device, of approved design in each lead wire.

A high-potential machine which, on account of great weight or for other reasons, can not have its frame insulated from the ground, should be surrounded with an insulated platform. This may be made of wood, mounted on insulating supports, and so arranged that a man must always stand upon it in order to touch any part of the machine.

In case of a machine having an insulated frame, if there is trouble from static electricity due to belt friction, it should be overcome by placing near the belt a metallic comb connected with the earth, or by grounding the frame through a very high resistance of not less than 300,000 ohms.

Welding Dynamos.-These are of the alternating type and must be installed with all the care used for any dynamo of like voltage and capacity.

Electrolysis and Plating Dynamos.-These are of the constant current type, and although often of low voltage are of great volume, hence must be thoroughly insulated from combustible material.

Storage or Primary Batteries.-These batteries are used for

storing up electricity and are highly charged; it thus becomes necessary to prevent any leakage of electricity by water on the sides of the jars, etc., to the ground, or burning out of connections on account of using any metals liable to corrosion in them (for the batteries being highly charged and being liable to give off a greater current than rated for, if the connections become corroded and thus weakened, they are apt to be burned out by the current) ; hence it is that the batteries must be mounted on glass or porcelain insulators and that their connections must not be made with any metal subject to corrosion.

In charging the batteries explosive gases are apt to be formed from the action of the current; it is therefore necessary to have the batteries located in well ventilated places. The same regulations as apply to similar apparatus fed from dynamo generators developing the same difference of potential must be observed with batteries.

SWITCH BOARDS AND SWITCH BOARD APPARATUS.-Switch Board. From the brushes the wires or conductors carry the electric current to the switch board, where are located the measuring, regulating and distributing apparatus. Here the hazards are from moisture forming arcs, from the arcs formed when the switches carrying currents are opened, where large fuses are on the board from the hot metal thrown or falling in event of a fuse melting, from over-heated rheostats and from defective instruments producing and holding arcs; hence the board should be made of some non-combustible material (such as the best polished white marble, free from cracks and metallic veins, or the best of slate free from metallic veins supported on iron framing), or of a solid, heavy, skeleton frame of hardwood, filled to prevent absorption of moisture. The board must have a clear space of eighteen inches between it and the floor, two feet between it and any ceiling which is not fireproof, and when connections are on the back of it must be accessible from all sides; if the connections are on the face of the board it may be placed against a brick or stone wall; the board must also be so located as to be free from moisture, and as to reduce to a minimum the danger of communicating fire to adjacent combustible material.

Conductors from generators to switchboard, rheostat or other

instruments, and thence to outside lines must be in plain sight and readily accessible and must be properly covered with an approved insulating material, and where in central stations, on exposed circuits, the wire which is used must have a heavy braided noncombustible outer covering.

Bus Bar; also called Bus Rod, Bus Wire.-A large copper conductor which takes the current from several dynamos and passes it to the distributing leads; the bar is bare, no insulation covering being called for. The bars must be kept so rigidly in place that they cannot come in contact. As the bar is subject to overheating, it must be mounted on glass or porcelain insulators on the face of the board. In a 2-wire system there are 2 bars, and in a 3-wire system 3 bars.

Rheostat, also called Resistance Box.—An apparatus for changing the resistance without opening the current and is generally built up of a number of resistance coils of iron or German silver set in a frame, and each one connected to one of a series of brass contact points set in a circle, or arc, on the face of the frame; a pivotal arm of brass is so set as to move over and in touch with the series of contact points, and it is by the moving of this arm that the proper amount of resistance is introduced into the circuit; the resistance is in reality an opposition to the free flow of the current, and this opposition is the cause of a considerable energy being dissipated in the form of heat, consequently there is a very considerable liability to the production of combustion in near by material; to reduce this hazard, no inflammable materials must be near the coils, hence the rheostat frame, meaning the entire case, must be of some non-combustible material, and if the rheostat is not on the switch board it must be placed at a distance of a foot from combustible material, or separated therefrom by a non-inflammable, non-absorptive insulating material, such as asbestos or glass, and it is much safer in the latter case to cover the combustible material with asbestos and then mount the rheostat on glass insulators over the asbestos.

Voltmeter.-A register for measuring the voltage of electromotive force, and is usually placed on the switch board so as to be readily seen. There is no special hazard to it.

Ampere-Meter, also called Ammeter.—A register for measuring the amperage or current throughout the entire line or circuit,