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series grouping all but one bell must be changed to a singlestroke action, so that each impulse of current will produce only one movement of the hammer. The current is then

B

FIG. 3.

interrupted by the vibrator in the remaining bell, the result being that each bell will ring with full power. The only change necessary to

produce this effect is to cut out the circuit-breaker on all but one bell by connecting the ends of the magnet wires directly to the bell terminals.

When it is desired to ring a bell from one of two places some distance apart, the wires may be run as shown in Fig. 4. The pushes p, p' are located at the required points, and the battery and bell are put in series with each other across the wires joining the pushes.

A single wire may be used to ring signal bells at each end of a line, the connections

FIG. 4.

PO

being given in Fig. 5. Two batteries are required, B and B', and a key and bell at each station. The keys k, k' are of the double-contact type, making connections normally between

B

L

G

bell b or b' and line wire L.

FIG. 5.

When one key, as k, is depressed, a current from B flows along the wire through the upper contact of k' to bell b' and back through ground plates G', G.

When a bell is intended for use with burglar-alarm apparatus, a constant-ringing attachment may be introduced, which closes the bell circuit through an extra wire as soon as the trip at door or window is disturbed. In the diagram, Fig. 6, the main circuit, when the push p is depressed, is through the automatic drop d by way of the terminals a, b to the bell

and battery. This

FIG. 6.

current releases a pivoted arm which, on falling, completes the circuit between b and c, establishing a new path for the current by way of e, independent of the push p.

For operating electric bells, any good type of open-circuit battery may be used. The Leclanché cell is largely used for this purpose, also several types of dry cells.

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ANNUNCIATOR SYSTEM.

30

The wiring diagram for a simple annunciator system is shown in Fig. 1. The pushes 1, 2, 3, etc. are located in the various rooms, one side being connected to the battery wire b, and the other to the leading wire in communication with the annunciator drop corresponding to that room. A battery of 2 or 3 Leclanché cells is placed at B in any convenient location. The size of wire used throughout may be No. 18 annunciator wire.

FIG. 1.

A return-call system is illustrated in Fig. 2, in which there is one battery wire b, one return wire r, and one leading wire 1, 12, etc. for each room. The upper portion of the annunciator board is provided with the usual drops, and below these are the

return-call pushes. These are double-contact buttons, held normally against the upper contact by a spring. When in this position, the closing of the circuit by the push button in any room, such as No. 4, rings the office bell and releases No. 4 drop, the path of the current in this case being from

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push 4 to a-c-d-e-f-g-B-h-b back to the push button. On the return signal being made by pressing the button at the lower part of the annunciator board, the office-bell circuit is broken at d, and a new circuit formed through k as follows: From the battery B to g-m-r-n-o-a-c-k-p to battery, the room bell being in this circuit. A general fire-alarm may be added to this system, consisting of an automatic clockwork apparatus for closing all the room-bell circuits at once, or as many at a time as a battery can ring. When this system is installed, the battery wire should be either No. 14 or No. 16. Four or five Leclanché cells are usually required in this case.

FIG. 2.

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It will be seen that the connections are so arranged that the room bell will ring when the push in that room is pressed. If this be not desired, a double-contact push may be substituted, so that the room-bell circuit is broken at the same time that the circuit is made through the annunciator. This double push should be so connected that the circuit is normally complete through the bell, the leading wire being connected to the tongue and the battery wire being connected to the second contact point, which is normally out of circuit.

EXTRACT FROM THE REGULATIONS OF THE UNDERWRITERS' ASSOCIATION.

Incandescent Wires.-Conducting wires, carried over or attached to buildings, must be (a) at least 7 ft. above the highest point of flat roofs, and (b) 1 ft. above the ridge of pitch roofs; (c) when in proximity to other conductors likely to divert any portion of the current, they must be protected by guard irons or wires, or a proper additional insulation, as the case may require.

For entering buildings, (a) wires with an extra-heavy waterproof insulation must be used; (b) they must be protected by drip loops; (c) also protected from abrasion by awning frames; (d) be at least 6 in. apart; (e) the holes through which they pass in the outer walls of such buildings must be bushed with a non-inflammable, waterproof, insulating tube, and (ƒ) should slant upward toward the inside.

(a) Wires must never be left exposed to mechanical injury, or to disturbance of any kind. (b) Wires must not be fastened by metallic staples. (c) When wires pass through walls, floors, partitions, timbers, etc., glass tubing, or so-called "floor insulators," or other moisture-proof, non-inflammable insulating tubing must be used. (d) At all outlets to and from cut-outs, switches, fixtures, etc., wires must be separated from gas pipes or parts of the building by porcelain, glass, or other non-inflammable insulating tubing, (e) and should be left in such a way as not to be disturbed by the plasterers. (f) Wires of whatever insulation must not in any case be taped, or otherwise be fastened, to gas piping. (g) If no gas pipes are installed at the outlets, an approved substantial support must be provided for the fixtures.

In crossing any metal pipes, or any other conductor, (a) wires must be separated from the same by an air space of at least in., where possible, and (b) so arranged that they cannot come in contact with each other by accident. (c) They should go over water pipes, where possible, so that moisture will not settle on the wires.

In unfinished lofts, between floors and ceilings, in partitions, and other concealed places, wires must (a) be kept free of contact with the building; (b) be supported on glass,

porcelain, or other non-combustible insulators; (c) have at least 1 in. clear air space surrounding them; (d) be at least 10 in. apart, when possible; and (e) should be run singly on separate timbers or studding. (f) When thus run in perfectly dry places, not liable to be exposed to moisture, a wire having simply a non-combustible insulation may be used.

Soft rubber tubing is not desirable as an insulator.

Care must be taken that the wires are not placed above each other in such a manner that water could make a crossconnection.

On all loops of incandescent circuits, safety catches must be used on both sides of the loop, and switches on such loops should be double-poled.

Wires must not be fished (a) for any great distance, and (b) only in cases where the inspector can satisfy himself that the above rules have been complied with. (c) Twin wires must never be employed in this class of concealed work.

Dynamo Machines.-Dynamo machines must be located in dry places, not exposed to flyings or easily combustible material, and insulated upon wooden foundations. The machines must be provided with devices that shall be capable of controlling any changes in the quantity of the current; and if the governors are not automatic, a competent person must be in attendance near the machine whenever it is in operation.

Each machine must be used with complete wire circuits; and connections of wires with pipes, or the use of circuits in any other method, are absolutely prohibited.

The whole system must be kept insulated, and tested every day with a magneto for ground connections in ample time before lighting, to remedy faults of insulation, if they are discovered; and proper testing apparatus must in each case be provided. This applies to both central station and isolated plants.

Testing circuits for grounds with a battery and bell is not considered a reliable test.

Preference is given to switches constructed with a lapping connection, so that no electric arc can be formed at the switch when it is changed; otherwise the stands of switches, where

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