weak and joints get loose, the best way is to install the switch so that when opened the blade will fall away from the contact. When thus installed the switch cannot become closed by any accident except the carelessness of an attendant, or the interference of some meddlesome person of an investigating turn of mind.

Fixtures.-Fixtures are always weak points in the insulation of electrical wiring in a building. As gas pipes are directly connected to the ground, any defective insulation of a circuit in a fixture immediately "grounds" our conductor. To secure insulation therefore we insulate our wire, insulate the conducting parts of our sockets from the fixture, and then, as an additional precaution, we insulate the fixture itself from the gas pipe. We speak now of what is called a "combination fixture," i. e., a fixture carrying both gas and electric lights. In order to insulate the fixture itself and at the same time leave an opening for the gas to flow into the pipe of the fixture, we use what is known as an insulating joint. This joint is inserted into the gas pipe just below the ceiling. There are innumerable varieties of these insulating joints, some of them pretty good, but most of them pretty bad. They have been made with all kinds of insulation, hard rubber, soft rubber, glass, leather, and everything else that has ever been used as an insulator. The only rule to follow in selecting a joint is to use one that has been tested and approved by the underwriters. As we must insulate all

fixtures from gas pipes, we must, of course, also insulate our conductors from the gas pipes, and must keep them away from them altogether. Where the gas pipe

comes through a wall or ceiling we place an insulating joint, but between the joint and the wall or ceiling the pipe is grounded, we must therefore keep our wires away from this part of the pipe. The shell referred to in section "b" is the "canopy" which covers the hole where the pipe comes through the wall or ceiling. This canopy should be fastened to the fixture below the insulating joint, it should be free from the ceiling and should be large enough so that the joints in the wires inside can be kept well away from the uninsulated part of the pipe. It has in the past been quite a popular practice to transform old gas fixtures into combination fixtures by attaching sockets to them and running the wires to the sockets on the outside of the fixture. This kind of work was not ornamental at best, and the efforts made to prevent the appearance being very ugly resulted in pretty poor insulation. Section "c" refers to this class of work. To secure good insulation and a neat appearance with this kind of work is more trouble and expense than a combination fixture is worth. The practice is not now very common, but a fixture when wired this way should be wired for safety rather than beauty. Although in ordinary wiring no wire should be used smaller than No. 14 B. & S. or 16 B. W. G. gauge, it is sometimes necessary to use a smaller wire in a fixture carrying a few lights, as the space for wire in a fixture is often very limited. In using this fine wire, however, we should remember that the table of safe carrying capacities only allows a current of three amperes in a No. 18 B. & S. wire. Section "e" is to prevent the mechanical injury of the insula

st for

wire, while it is being drawn into a fixture. f" applies to an electric (not a combination) e., a fixture carrying only electric lights. It is the insulation from our old enemy moisture. g" is for the mechanical protection of the of a wire, in a combination fixture. In a n fixture wires are run between the gas pipe rounding ornamental shell, as it is the only in them and have them concealed. It is a is the practice of fixture manufacturers has ild a fixture so that nothing larger than bell be hauled into it. All fixtures should be tested in the shop where they are wired, and they are up in place and before the wires in are connected to the wires in the building. d test shows any injury to insulation that een caused in the installing of the fixture, ame time shows whether the insulating joint ulates the fixture itself. When combination used they are attached to the gas pipes, but e electric fixtures are used they must be some support provided for that purpose. asible it would be well to use an insulating of material for a support, but, in practice, Is usually supported from a wooden block, ened to the ceiling. When thus supported ould be treated as in cases where they pass is and ceilings, and be separated from any by insulating and non inflammable bushings. bes of convenient form and size are the purpose

CHAPTER XV.

CLASS C, LOW POTENTIAL SYSTEMS.

PART IX.

TEXT OF THE CODE COVERED BY THIS CHAPTER. 28. ARC LIGHTS ON LOW POTENTIAL CIRCUITS:-a. Must be supplied by branch conductors not smaller than 12 B. & S. gauge. b. Must be connected with main conductors only through double pole cutouts. c. Must only be furnished with such resistances or regulators as are enclosed in non-combustible material, such resistances being treated as stoves. Incandescent lamps must not be used for resistance devices. d. Must be supplied with globes and protected as in the case of arc lights on high potential circuits.

29. ELECTRIC GAS LIGHTING:-Where electric gas lighting is to be used on the same fixture with the electric light: a. No part of the gas piping or fixture shall be in electrical connection with the gas lighting circuit. b. The wires used with the fixtures must have a non-inflammable insulation, or, where concealed between the pipe and the shell of the fixture, the insulation must be such as required for fixture wiring for the electric light. c. The whole installation must test free from "grounds." d. The two installations must test perfectly free from connection with each other.

30. SOCKETS:- -a. No portion of the lamp socket exposed to contact with outside objects must be allowed to come into electrical contact with either of the conductors. b. In rooms where inflammable gases may exist, or where the atmosphere is damp, the incandescent lamp and socket should be enclosed in a vaportight globe.

31. FLEXIBLE CORD:-a. Must be made of conductors, each surrounded with a moisture-proof and non-inflammable layer, and further insulated from each other by a mechanical separator of

carbonized material. Each of these conductors must be composed of several strands. b. Must not sustain more than one light not exceeding 50 candle power. c. Must not be used except for pendants, wiring of fixtures and portable lamps or motors. d. Must not be used in show windows. e. Must be protected by insulating bushings where the cord enters the socket. The ends of the cord must be taped to prevent fraying of the covering. f. Must be so suspended that the entire weight of the socket and lamp will be borne by knots under the bushing in the socket and above the point where the cord comes through the ceiling block or rosette, in order that the strain may be taken from the joints and binding screws. g. Must be equipped with keyless sockets as far. as practicable, and be controlled by wall switches.

32. DECORATIVE SERIES LAMPS:-Incandescent lamps run in series circuits shall not be used for decorative purposes inside of buildings.

Although arc lamps are for the most part operated in series, and upon high potential systems, still there is no difficulty in operating them on low potential systems, as the ordinary arc lamp requires only a pressure of 45 to 50 volts. Thousands of lamps are so operated, and the practice is becoming daily more common. The only difference in the two methods of operation is that, when arc lamps are operated in series on high potential systems, a lamp is extinguished or cut out by shunting the current, i.e., connecting together the two wires entering the lamp by a low resistance path; while on a low potential system the lamp is cut out or extinguished by opening the circuit to the lamp. An ordinary arc lamp takes a current of five, six or ten amperes, and, as seen by the table already given, the code allows a current of 12 amperes in a No. 14 wire (B. & S. gauge) when it is concealed and 16 amperes when it is exposed.