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the ground, and the room in which they are placed be practically air-tight, except that it shall be thoroughly ventilated to the out-door air, if possible, through a chimney or flue. 35. Primary Conductors:

a. Must each be heavily insulated with a coating of moisture-proof material from the point of entrance to the transformer, and, in addition, must be so covered and protected that mechanical injury to them, or contact with them, shall be practically impossible.

b. Must each be furnished, if within a building, with a switch and a fusible cutout where the wires enter the building, or where they leave the main line, on the pole or in the conduit. These switches should be enclosed in secure and fireproof boxes, preferably outside the building.

c. Must be kept apart at least ten inches, and at the same distance from all other conducting bodies when inside a building.

36. Secondary Conductors:

Must be installed according to the rules for "Low Potential Systems."

Class E.

ELECTRIC RAILWAYS.

37. All rules pertaining to arc-light wires and stations shall apply (so far as possible) to street railway power stations and their conductors in connection with them.

38. Power Stations:

Must be equipped in each circuit as it leaves the station with an approved automatic "breaker," or other device that will immediately cut off the current in case the trolley wires become grounded. This device must be mounted on a fireproof base and in full view and reach of the attendant. (See Definitions).

39. Trolley Wires:—

a. Must be no smaller than No. 0 B. & S. copper, or No. 4 B. & S. silicon bronze, and must readily stand the strain put upon them when in use.

b. Must be well insulated from their supports, and in case of the side or double pole construction, the supports shall also be insulated from the poles immediately outside of the trolley wire.

c. Must be capable of being disconnected at the power house, or of being divided into sections, so that in case of fire on the railway route the current may be shut off from the particular section, and not interfere with the work of the firemen. This rule also applies to feeders.

d. Must be safely protected against contact with all other conductors.

40. Car Wiring:

Must be always run out of reach of the passengers, and must be insulated with a waterproof insulation.

41. Lighting And Power From Railway Wires:

Must not be permitted, under any pretense, in the same circuit with trolley wires with a ground return, nor sball the? same dynamo be used for both purposes, except in street railway cars, electric car houses, and their power stations*

42. Car Houses:

Must have special cut-outs located at a proper distance outside, so that all circuits within any car house can be cut out at one point.

43. Ground Return Wires:

Where ground return is used it must be so arranged that no difference of potential will exist greater than 5 volts to 50 feet, or 50 volts to the mile between any two points in the earth or pipes therein.

Class F.

44. Storage Or Primary Batteries:

a. When current for light and power is taken from primary or secondary batteries, the same general regulations must be observed as apply to similar apparatus fed from dynamo generators developing the same difference of potential.

b. All secondary batteries must be mounted on approved insulators.

c. Special attention is directed to the rules (page 173) for rooms where acid fumes exist.

d. The use of any metal liable to corrosion must be avoided in connections of secondary batteries.

MISCELLANEOUS. 45. a. The wiring in any building must test free from grounds; i. e., each main supply line and every branch circuit shall have an insulation resistance of at least 25,000 ohms, and should have an insulation resistance between conductors and between all conductors and the ground (not including attachments, sockets, receptacles, etc.), of not less than the following:—

Up to 10 amperes 4,000,000

"25" 1,600,000

"50" 800 000

"100" 300,000

"200" 160,000

"400" 80,000

"800" 22,000

"1600" 11,000

All cut-outs and safety devices in place in the above.

Where lamp sockets, receptacles and electroliers, etc., are connected, one-half of the above will be required.

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