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other conductors, the wires must all be rigidly secured and separated from each other or any other conductors by means of some rigid nonconducting material.
14. Arc wires of opposite polarities (1. e., the incoming and outgoing wires from each lamp or of each circuit) must be kept at a distance not less than eight inches from each other, except within the structure of lamps or on switchboards, cut-out boxes, or the like, where a nearer approach is necessary.
15. In exceptional cases, however, where the wires are so rigidly secured and insulated that contact or connection between them is quite impossible, they may be allowed to approach much nearer. (E. g. If each wire or conductor is covered with a thick and indisplaceable insulation, which in turn is covered by a leaden sheath or pipe, and then two or more such pipes are inclosed in an iron pipe in such manner that injury to the lead covered cables is impossible, this would be an allowable substitute for the eight inches of absolute separation called for in the general rule.)
16. Wherever wires are carried through walls, partitions, or floors within a building, they must be surrounded by a special rigid insulating tube or casing impervious to water, and must be so attached and supported as to be secure from abrasion or other mechanical injury.
(Note.-Rubber tubing will not meet the above requirement as an insulation.)
17. The exterior frames and other exposed parts of arc lamps must be securely insulated from the electric circuit, and all such lamps must have glass globes surrounding the light and inclosed below, so as to prevent the fall of ignited particles. Where inflammable materials are placed below such lamps, the globe must be surrounded by a wire netting capable of keeping the parts of the globe in place if it is fractured in use.
(Note.—Broken globes must be replaced as soon as practicable by new ones.)
18. In show windows and other places where inflammable materials are displayed, and in factories or wood-working establishments where “flyings” may be present in the air, each lamp must be provided with “spark arresters.”
19. Each lamp must be provided with a hand switch, and also with an automatic switch which shall shunt the current round the carbons before the arc between them reaches a dangerous length.
LOW POTENTIAL SYSTEMS.
20. In direct incandescent systems, the rules as to the capacity, location, and arrangement of conductors are substantially the same as has been already stated, with the following exceptions:
21. In case the difference of potential at the positive and negative posts of the dynamo or dynamos developing the current is not more than 250 volts, the positive and negative wires in aerial lines and elsewhere which would otherwise be required to maintain a minimum distance of ten inches, may be brought to within six inches of each other. Also underground conductors may be inclosed both in the same tube, and if rigidly and securely supported, and surrounded by and imbedded in a solid insulating substance, may lie within one-quarter inch of each other.
22. When underground service conductors enter a building care must be taken that they are at once separated to the required distance (see below), and are adequately and permanently insulated from each other and from the pipe in which they were inclosed, if they were inclosed in a metallic pipe or conduit.
23. They must also be adequately protected from mechanical injury, and must be so located that a cut-out can be safely and conveniently located close to the end of the service pipe or conduit by which they are brought in.
Low Potential Wires Within Buildings.
24. In the distribution of the conductors through buildings, “concealed work,” such as the placing of wires under floors or within
partitions, walls, or ceilings, should be avoided as much as possible.
25. In perfectly and securely dry localities an approved insulated wire without waterproof covering may be used, provided the wires are not concealed and are supported by cleats or insulators.
26. Wherever the wires are to be in any way covered up they must be coated with an approved waterproof insulation, or otherwise protected in such manner as may be from time to time aproved by the Committee.
27. In all cases of concealed work, the company proposing to introduce the same will be required to furnish the Board with a detailed diagram of the work, showing the kind and size of wire used at the different branches, with particulars as to the insulation and in what materials imbedded, location of cutouts, switches, etc. The diagram to be signed and sworn to by an officer of the company, and filed with the Board for reference.
28. If wires are imbedded in the plaster of walls, ceilings, or partitions, they must be separated not less than ten inches from each other, in addition to being insulated as above described, unless they are inclosed in approved conduits.
29. In buildings in course of construction, terminal wires must be so arranged as to be secure from injury by the plasterers.
30. Wires insulated as above may be covered by or imbedded in moldings in dry locations, but in breweries, paper mills, dye-houses, and other like places where they are exposed to moisture, they must be carried out of contact with the walls, ceilings, and the like, on approved “insulators,” or in such waterproof and insulating conduits as may be approved by the Committee.
31. Conduits to be approved must be continuous from one junction box to another or to fixtures, and be of material that will resist the fusing of wire or wires they contain without destroying or igniting the conduit; and if not entirely imbedded in plaster or other noninflammable material or not inflammable themselves, must have an outer covering that is non-inflammable, and be so placed that they will be protected from injury and breakage; and all wires intended to carry more than five-ampère currents shall be placed in separate conduits unless a special permit is issued for same; on branches intended for wires of five-ampère currents and less, the positive and negative wires, if properly insulated, may be placed in the same conduit, provided a double pole safety fuse is inserted at each branch connection.
Secondary Systems. 32. In these systems where alternating currents of high electromotive force are used on