d. Circuit-breakers must operate successfully, under the most severe conditions they are liable to meet with in practice, on short circuits when set at fifty per cent above the current, and with a voltage twenty-five per cent above that for which they are designed. e. Must be plainly marked, where it will always be visible, with the name of the maker, and current and voltage for which the device is designed. 53. Fuses (For installation rules, see Nos. 17 and 21.) a. Must have contact surfaces or tips of harder metal having perfect electrical connection with the fusible part of the strip. b. Must be stamped with about eighty per cent of the maximum current they can carry indefinitely, thus allowing about twenty-five per cent overload before fuse melts. With naked open fuses, of ordinary shapes and not over 500 amperes capacity, the maximum current which will melt them in about five minutes may be safely taken as the melting point, as the fuse practically reaches its maximum temperature in this time. With larger fuses a longer time is necessary. Inclosed fuses where the fuse is often in contact with substances having good conductivity to heat and often of considerable volume, require a much longer time to reach a maximum temperature, on account of the surrounding material which heats up slowly. These data are given to facilitate testing. c. Fuse terminals must be stamped with the maker's name, initials, or some known trade-mark. 54. Cutout Cabinets a. Must be so constructed, and cutouts so arranged, as to obviate any danger of the melted fuse metal coming in contact with any substance which might be ignited thereby. A suitable box can be made of marble, slate, or wood, strongly put together, the door to close against a rabbet so as to be perfectly dust-tight, and it should be hung on strong hinges, and held closed by a strong hook or catch. If the box is wood, the inside should be lined with sheets of asbestos board about one-sixteenth of an inch in thickness, neatly put on and firmly secured in place by shellac and tacks. The wire should enter through holes bushed with porcelain bushings; the bushings tightly fitting the holes in the box, and the wires tightly fitting the bushings (using tape to build up the wire, if necessary) so as to keep out the dust. 55. Sockets (See No. 27.) Sockets of all kinds, including wall receptacles, must be constructed in accordance with the following specifications: a. STANDARD SIZES.- The standard lamp socket shall be suitable for use on any voltage not exceeding 250 and with any size lamp up to fifty candlepower. For lamps larger than fifty candle-power a standard keyless socket may be used, or if a key is required, a special socket designed for the current to be used must be made. Any special sockets must follow the general spirit of these specifications. b. MARKING.-The standard socket must be plainly marked fifty candlepower, 250 volts, and with either the manufacturer's name or registered trade mark. Special large sockets must be marked with the current and voltage for which they are designed. c. SHELL.- Metal used for shells must be moderately hard, but not hard enough to be brittle or so soft as to be easily dented or knocked out of place. Brass shells must be at least 0.013 inch in thickness, and shells of any other material must be thick enough to give the same stiffness and strength of brass. d. LINING. The inside of the shells must be lined with insulating material, which shall absolutely prevent the shell from becoming a part of the circuit, even though the wires inside the socket should start from their position under binding screws. The material used for lining must be at least one-thirty-second of an inch in thickness, and must be tough and tenacious. It must not be injuriously affected by the heat from the largest lamp permitted in the socket, and must leave the water in which it is boiled practically neutral. It must be so firmly secured to the shell that it will not fall out with ordinary handling of the socket. It is preferable to have the lining in one piece. e. CAP.-Caps when of sheet brass must be at least 0.013 inch in thickness, and when cast or made of other metals must be of equivalent strength. The inlet piece, except for special sockets, must be tapped and threaded for ordinary one-eighth-inch pipe. It must contain sufficient metal for a full, strong thread, and, when not of the same piece as the cap, must be joined to it in a way to give the strength of a single piece. There must be sufficient room in the cap to enable the ordinary wireman to easily and quickly make a knot in the cord and push it into place in cap without crowding. All parts of the cap upon which the knot is likely to bear must be smooth and well insulated. f. FRAME AND SCREWS.-The frame holding moving parts must be sufficiently heavy to give ample strength and stiffness. Brass pieces containing screw threads must be at least 0.06 of an inch in thickness. Binding post screws must not be smaller than No. 5 wire and about forty threads per inch. g. SPACING.- Points of opposite popularity must everywhere be kept not less than three-sixty-fourths of an inch apart unless separated by a reliable insulation. h. CONNECTIONS.- The connecting points for the flexible cord must be made to very securely grip a No. 16 or 18 B. & S. conductor. A turned-up lug, arranged so that the cord may be gripped between the screw and the lug in such a way that it cannot possibly come out, is strongly advised. i. LAMP HOLDER.- The socket must firmly hold the lamp in place so that it cannot be easily jarred out, and must provide a contact good enough to prevent undue heating with maximum current allowed. The holding pieces, springs and the like, if a part of the circuit, must not be sufficiently exposed to allow them to be brought in contact with anything outside of lamp and socket. j. BASE. The inside parts of the socket, which are of insulating material, except the lining, must be made of porcelain. k. KEY.- The socket key-handle must be of such a material that it will not soften from the heat of a fifty candle-power lamp hanging downwards in air at seventy degrees Fahrenheit from the socket, and must be securely, but not necessarily rigidly, attached to the metal spindle it is designed to turn. 1. SEALING.—All screws in porcelain pieces, which can be firmly sealed in place, must be so sealed by a waterproof compound which will not melt below 200 degrees Fahrenheit. m. PUTTING TOGETHER. The socket must, as a whole, be so put together that it will not rattle to pieces. Bayonet joints or equivalent are recommended. n. TEST.- The socket when slowly turned "on and off," at the rate of about two or three times per minute, must "make and break" the circuit 6,000 times before failing, when carrying a load of one ampere at 220 volts. 0. KEYLESS SOCKETS. - Keyless sockets of all kinds must comply with requirements for key sockets as far as they apply. p. SOCKETS OF INSULATING MATERIALS. — Sockets made of porcelain or other insulating material must conform to the above requirements as far as they apply, and all parts must be strong enough to withstand a moderate amount of hard usage without breaking. 9. INLET BUSHING.— When the socket is not attached to fixtures the threaded inlet must be provided with a strong insulating bushing, having a smooth hole of at least fifteen-sixty-fourths of an inch in diameter. The corners of the bushing must be rounded and all inside fins removed, so that in no place will the cord be subjected to the cutting or wearing action of a sharp edge. 56. Hanger-boards a. Hanger-boards must be so constructed that all wires and current-carrying devices thereon shall be exposed to view, and thoroughly insulated by being mounted on a non-combustible, non-absorptive insulating substance. All switches attached to the same must be so constructed that they shall be automatic in their action, cutting off both poles to the lamp, not stopping between points when started, and preventing an arc between points under all circumstances. 57. Arc Lamps — (For installation rules, see No. 19.) a. Must be provided with reliable stops to prevent carbons from falling out in case the clamps become loose. b. Must be carefully insulated from the circuit in all their exposed parts. c. Must, for constant-current systems, be provided with an approved hand switch, also an automatic switch that will shunt the current around the carbons, should they fail to feed properly. The hand switch to be approved, if placed anywhere except on the lamp itself, must comply with requirements for switches on hanger-boards as laid down in No. 56. 58. Spark Arresters (See No. 19 c.) a. Spark arresters must so close the upper orifice of the globe that it will be impossible for any sparks thrown off by the carbons to escape. a. Must be entirely made of material that will resist the action of illuminating gases, and will not give way or soften under the heat of an ordinary gas flame or leak under a moderate pressure. They shall be so arranged that a deposit of moisture will not destroy the insulating effect, and shall have an insulating resistance of at least 250,000 ohms between the gas pipe attachments, and be sufficiently strong to resist the strain they will be liable to be subjected to in being installed. b. Insulating joints having soft rubber in their construction will not be approved. 60. Resistance Boxes and Equalizers (For installation rules, see No. 4.) a. Must be equipped with metal, or with other non-combustible frames. The word "frame" in this section relates to the entire case and surroundings of the rheostat, and not alone to the upholding supports. 61. Reactive Coils and Condensers a. Reactive coils must be made of non-combustible material, mounted on non-combustible bases, and treated, in general, like sources of heat. b. Condensers must be treated like apparatus operating with equivalent voltage and currents. They must have non-combustible cases and supports, and must be isolated from all combustible materials, and, in general, treated like sources of heat. 62. Transformers (For installation rules, see Nos. 11, 13, and 33.) a. Must not be placed in any but metallic or other non-combustible cases. b. Must be constructed to comply with the following tests: 1. Shall be run for eight consecutive hours at full load in watts under conditions of service, and at the end of that time the rise in temperature, as measured by the increase of resistance of the primary coil, shall not exceed 135 degrees Fahrenheit. 2. The insulation of transformers when heated shall withstand continuously for five minutes a difference of potential of 10,000 volts (alternating) between primary and secondary coils and core, and between the primary coils and core and a no-load "run" at double voltage for thirty minutes. 63. Lightning Arresters (For installation rules, See No. 5.) a. Must be mounted on non-combustible bases, and must be so constructed as not to maintain an arc after the discharge has passed, and must have no moving parts. CLASS E. MISCELLANEOUS. 64. Signaling Systems (governing wiring for telephone, telegraph, district messenger, and call-bell circuits, fire and burglar alarms, and all similar systems) a. Outside wires should be run in underground ducts or strung on poles and, as far as possible, kept off of buildings, and must not be placed on the same cross-arm with electric light or power wires. b. When outside wires are run on same pole with electric light or power wires, the distance between the two inside pins of each cross-arm must not be less than twenty-six inches. c. All aerial conductors and underground conductors which are directly connected to aerial wires must be provided with some approved protective device, which shall be located as near their point of entrance to the building as possible, and not less than six inches from curtains or other inflammable material. d. If the protector is placed inside of building, wires, from outside support to binding-posts of protector, shall comply with the following require ments: 1. Must be of copper, and not smaller than No. 16 B. & S. gauge. 5. Must be supported on porcelain insulators, so that they will not come 6. A separation between wires of at least two and one-half inches must be maintained. In case of crosses these wires may become a part of a high-voltage circuit, so that similar care to that given high-voltage circuits is needed in placing them. Reliable porcelain bushings at the entrance holes are desirable, and are only waived under adverse conditions, because the state of the art in this type of wiring makes an absolute requirement inadvisable. e. The ground wire of the protective device shall be run in accordance with the following requirements: 1. Shall be of copper, and not smaller than No. 16 B. & S. 2. Must have an approved rubber insulating covering (see No. 41). |