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dynamo without in any manner affecting the operation of the dynamos remaining in circuit or the candle-power of the lamps, and will permit the cutting in or out of any circuit without affecting the stability of other circuits. For systems operating one dynamo for each circuit or series of circuits the connections shall be such as will permit any circuit to be connected to or disconnected from any dynamo with certainty and rapidity. (For switchboard connections see sees. 30 and 31, pp. 55 and 56.

42. circuits. (See p. 57, sec. 32.)

Constant Potential, Alternating Current
System.

This contractor shall furnish, and, unless otherwise specified, erect the folio wling apparatus and material:

(See Note: p. 43, sec. 21.) 43. Dynamo®.

constant potential, alternating

current dynamo(s) (each) having a capacity of kilowatts. The maximum

voltage at the terminals of the dynamo(s) shall not exceed volts.

The dynamo(s) shall be of the latest and most efficient pattern; mounted on a base provided with an adjustable belt tightener so that the belt may be tightened while in operation; capable of operating under full load for consecutive

hours without increasing the temperature of any part, especially the armature, fields and commutator, to such a degree as to endanger the insulation or decrease the efficiency of operation; shall have an insulation resistance of not less than

ohms between all parts insulated from each other; shall be adapted to operate at such speed as will allow the use of highspeed, automatic cut-off engines belted direct; shall be supplied with efficient oiling devices; the armature shall be balanced both electrically and mechanically so that there will be no tendency to spring the shaft, or to draw the armature toward either bearing so as to cause excessive friction and heating, and no vibration; all contacts, brushes, binding posts, etc., shall be so placed and protected that there is the least possible danger of receiving a shock. The dynamo(s) shall be rated with such

margin of safety that j | will not be

injured if subjected to an overload of

per cent, above such rating for a period of ;if self-exciting the coils furnishing the exciting current, and the commutator shall be so insulated and protected that it will be impossible under the ordinary conditions of operation to ground or cross them on themselves or on the armature circuit; if separately excited the exciting dynamo(s) also shall be subject to the general conditions given above, shall

operate at a potential not exceeding

volts, shall be of ample capacity to excite

the fields of dynamo(s) (each) having

a capacity of kilowatts, and shall

operate with no appreciable sparking at the brushes.

There shall be provided with each dynamo one ampere meter for indicating the current supplied by the dynamo; one voltmeter or pressure indicator which shall remain constantly in circuit so as to indicate continuously the pressure on the primary mains at the point to which it is connected, and shall be so constructed that the scale is plainly visible at a dis

(See p. 61, sec. 34.)

44. Foundations.

(See Note: p. 48, sec. 23.)

45. Instruments.

tance of at least ;one insulating baseframe provided with rails and a suitable device for shifting the position of the dynamo to alter the belt tension; one ground detector which shall continuously indicate the insulation maintained on both sides throughout the system; one pair of lightning arresters; for the field-exciting circuit one hand regulator made entirely of incombustible material, one voltmeter, one brush jig, one double-pole knife switch mounted on an incombustible base, one double-pole fusible cut-out mounted on an incombustible base; if the fields are separately excited there shall be provided with the exciting dynamo one insulating baseframe as above, one endless belt, and also, if it excites the fields of more than one dynamo, one hand regulator for the field circuit of the exciting dynamo, one hand regulator for each of the field circuits of the excited dynamos, and one double-pole knife switch and double-pole fusible cut-out for each of the above field circuits, including that of the exciting dy

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