For two-wire D. C. generators, single-pole protection will be considered as satisfying the above rule, provided the safety device is so located and connected that the means for opening same is actuated by the entire generator current, and the action thereof will completely open the generator circuit.

For three-wire direct-current generators compound or shunt wound, a safety device must be placed in each armature lead, and so connected as to receive the entire current from the armature. Fuses will not be acceptable. The safety device must consist of either: (1) a double pole, double coil, overload circuit breaker, or (2) a fourpole circuit breaker connected in the main and equalizer leads, and tripped by means of two overload devices, one in each armature lead.

The safety devices above required must be so interlocked that no one pole can be opened without simultaneously disconnecting both sides of the armature from the system.

e. Generators must each be provided with a name-plate, giving the maker's name, the capacity in volts and amperes, and the normal speed in revolutions per minute.

f. Terminal blocks when used on generators must be made of approved non-combustible, non-absorptive, insulating material, such as slate, marble or porcelain.

g. The use of soft rubber bushings to protect the lead wires coming through the frames of generators is permitted, except when installed where oils, grease, oily vapors or other substances known to have rapid deleterious effect on rubber are present in such quantities and in such proximity to the generator as may cause such bushings to be liable to rapid destruction. In such cases hard wood, properly filled, or preferably porcelain or micanite bushings must be used.

§ 202. Conductors from generators to switchboards, rheostats or other instruments, and thence to outside lines.-a. Conductors must be in plain sight or readily accessible. Wires from generator to switchboard may, however, be placed in a run-way in the brick or cement pier on which the generator stands. When protection against moisture is necessary, cable with grounded lead sheath or grounded conduit must be used.

b. Conductors must have an approved insulating covering as called for in article 4 of this chapter for similar work, except that in central stations, on exposed circuits, the wire which is used must have a heavy braided, non-combustible outer covering. Conductors used as bus bars may be made of bare metal. Wires with inflammable outer braiding, when brought close together, as in the rear of switchboards, must, when required, be each surrounded with a tight, noncombustible outer cover. Flame proofing must be stripped back on all cables a sufficient amount to give the necessary insulation distances for the voltage of the circuit on which the cable is used.

c. Conductors, must, where not in a conduit, be kept so rigidly in place that they cannot come in contact.

d. Conductors must in all other respects be installed, with the same precautions as required in article 4 of this chapter for wires carrying a current of the same volume and potential.

e. In wiring switchboards, the ground detector, voltmeter, pilot lights and potential transformers must be connected to a circuit of

not less than No. 14 B. & S. gage wire that is protected by approved fuses. This circuit is not to carry over 660 watts.

For the protection of instruments and pilot lights and switchboards, approved N. E. Code standard enclosed fuses are preferred, but approved enclosed fuses of other designs of not over two (2) amperes capacity may be used.

§ 203. Switchboards.-a. Switchboards must be so placed as to reduce to a minimum the danger of communicating fire to adjacent combustible material.

Switchboards must not be built up to the ceiling, a space of three feet being left, if possible, between the ceiling and the board. The space back of the board must be kept clear of rubbish and must not be used for storage purposes.

b. Switchboards must be made of non-combustible material.

c. Switchboards must be accessible from all sides when the connections are on the back, but may be placed against a brick or stone wall when the wiring is entirely on the face.

If the wiring is on the back, there must be a clear space of at least eighteen inches between the wall and the apparatus on the board, and even if the wiring is entirely on the face, it is much better to have the board set out from the wall.

d. Switchboards must be kept free from moisture.

e. Wires with inflammable outer braiding, when brought close together, as in the rear of switchboards, must, when required, be each surrounded with a tight, non-combustible outer cover.

Flame proofing must be stripped back on all cables a sufficient amount to give the necessary insulation distances for the voltage of the circuit on which the cable is used.

§ 204. Resistance devices.—a. Resistance devices must be placed on a switchboard, or at a distance of at least one foot from combustible material, or separated therefrom by a slab or panel of noncombustible, non-absorptive insulating material such as slate, soapstone or marble, somewhat larger than the rheostat, which must be secured in position independently of the rheostat supports. Bolts for supporting the rheostat shall be countersunk at least 1-8 inch below the surface at the back of the slab and the bolt heads shall be covered with insulating material. For proper mechanical strength, slab should be of a thickness consistent with the size and weight of the rheostat, but in no case less than 1/2 inch.

If resistance devices are installed in rooms where dust or combustible flyings are liable to accumulate on them, they must be equipped with dust-proof face-plates.

b. Where protective resistances are necessary in connection with automatic rheostats, incandescent lamps may be used, provided that they do not carry or control the main current nor constitute the regulating resistance of the device.

When so used, lamps must be mounted in porcelain receptacles upon non-combustible supports, and must be so arranged that they cannot have impressed upon them a voltage greater than that for which they are rated. They must in all cases be provided with a name-plate, which shall be permanently attached beside the porcelain receptacle or receptacles and stamped with the wattage and voltage of the lamp or lamps to be used in each receptacle.

Under special authorization in writing, given in advance, incandescent lamps may be used for the purpose of resistances in series with other devices when mounted in porcelain receptacles upon noncombustible supports and so arranged that they cannot have impressed upon them a voltage greater than that for which they are rated. c. Wherever insulated wire is used for connections between resistance elements and the contact device of a rheostat, the insulation must be of approved slow-burning or other heat-resisting type. For large rheostats and similar resistances, where the contact devices are not mounted upon them, the connecting wires having slow burning insulation may be so arranged in groups that the maximum difference of potential between any two wires in a group shall not exceed 75 volts. Each group of wires must either be mounted on non-combustible, non-absorptive insulators giving at least 1⁄2 inch separation from surface wired over, or, especially where it is necessary to protect same from mechanical injury, each group of wires may be encased in approved flexible tubing and placed in approved conduit, the flexible tubing to extend at least 1 inch beyond the ends of the conduit.

$205. Lightning arresters.-a. Lightning arresters must be attached to each wire of every overhead circuit connected with the station. b. Lightning arresters must be located in readily accessible places away from combustible materials, and as near as practicable to the point where the wires enter the building.

In all cases, kinks, coils and sharp bends in the wires between the arresters and the outdoor lines must be avoided as far as possible.

c. Lightning arresters must be connected with a thoroughly good and permanent ground connection by metallic strips or wires having a conductivity not less than that of a No. 6 B. & S. gage copper wire, which must be run as nearly in a straight line as possible from the arresters to the ground connection.

Ground wires for lightning arresters must not be attached to gas pipes within the buildings nor be run inside of iron pipes, unless electrically and mechanically attached to both ends of the pipe.

d. All choke coils or other attachments, inherent to the lightning protection equipment, shall have an insulation from the ground or other conductors equal at least to the insulation demanded at other points of the circuit in the station.

§ 206. Care and attendance.-a. A competent man must be kept on duty where generators are operating.

b. Oily waste must be kept in approved waste cans and removed daily.

§ 207. Testing of insulation resistance.-a. All circuits except such as are permanently grounded in accordance with § 315 of this chapter must be provided with reliable ground detectors. Detectors which indicate continuously and give an instant and permanent indication of a ground are preferable. Ground wires from detectors must not be attached to gas pipes within the building.

b. Where continuously indicating detectors are not feasible the circuits should be tested at least once per day, and preferably oftener.

§ 208. Motors.-a. Motors must, when operating at a potential in excess of 550 volts, have no exposed live metal parts, and must have their base frames permanently and effectively grounded.

Motors operating at a potential of 550 volts or less must have their base frames permanently and effectively grounded wherever feasible. Where grounding of the frame is impracticable, special permission for its omission may be given in writing, in which case the frame must be permanently and effectively insulated. Wooden base frames used for this purpose, and wooden floors, which are depended upon for insulation where, for any reason, it is necessary to omit the base frames, must be kept filled to prevent absorption of moisture, and must be kept clean and dry.

b. Motors operating at a potential of 550 volts or less must be wired with the same precautions as required by article 4 of this chapter, for wires carrying a current of the same volume.

Motors operating at a potential between 550 and 3,500 volts must, except in central or sub-stations, be wired with approved multiple conductor, metal sheathed cable in approved metal conduit. All apparatus and wiring connected to the high tension circuit must be completely enclosed in substantial grounded metal shields or casings, and the conduit must enter and be properly secured to such casings or to suitable terminal boxes screwed or bolted to the casings. The insulation of the several conductors for high-potential motors, where leaving the metal sheath of cables, must be thoroughly protected from moisture and mechanical injury. This may be accomplished by means of a pot head or some equivalent method. The conduit must be substantially bonded to the metal casings of all fittings and apparatus connected to the inside high-tension circuit.

Where outside wires directly enter the motor room, special permission, in writing, must be obtained to install the wires for high-potential motors according to the general rules for high-potential systems.

Conductors carrying the current of only one motor must be designed to carry a current at least 25 per cent. greater than that for which the motor is rated. Where the wires under this rule would be overfused in order to provide for the starting current, as in the case of many of the alternating current motors, the conductors must be of such size as to be properly protected by these larger fuses.

The current used in determining the size of the conductor carrying the current of only one varying (or variable) speed motor must be the percentage of the 30-minute current rating of the motor as given for the several classifications of service in the following table:

Hoists, rolls, ore and coal-handling machines.

150

Freight and passenger elevators, shop cranes, tool heads, pumps, etc..

120

c. Each motor with its starting device must be protected by a cut-out and controlled by a switch (see § 419a of this chapter),

said switch plainly indicating whether " "on or "off" (except as provided for electric cranes, see § 443c of this chapter). Small motors may be grouped under the protection of a single set of fuses, provided the rated capacity of the fuses does not exceed 10 amperes, and the total wattage of the circuit does not exceed 660. With motors of 4 horse power or less, on circuits where the voltage does not exceed 300, single pole switches may be used as allowed in § 424c of this chapter. The switch and rheostat must be located within sight of the motor, except in cases where special permission to locate them elsewhere is given in writing.

Where the circuit-breaking attachment on the motor-starting device disconnects all wires of the circuit, the switch called for in this section may be omitted.

Overload-release attachments on motor-starting rheostats will not be considered to take the place of the cut-out required by this section. An automatic circuit-breaker disconnecting all wires of the circuit may serve as both switch and cut-out.

Where a rubber-covered conductor carries the current of only one A. C. motor of a type requiring large starting current it may be protected by a fuse or an automatic circuit breaker without time limit device, rated in accordance with Table B of § 418 of this chapter. The rated continuous current capacity of a time limit circuit breaker protecting a motor of the above type need not be greater than 125 per cent. of the motor current rating, providing the time limit device is capable of preventing the breaker opening during the starting period.

d. Rheostats must be so installed as to comply with all the requirements of § 204 of this chapter. Auto starters must comply with requirements of § 204c of this chapter.

Auto starters, unless equipped with tight casings enclosing all current-carrying parts, in all wet, dusty or linty places, must be enclosed in approved cut-out boxes or cabinets. Where there is any liability of short circuits across their exposed live parts due to accidental contacts, a railing must be erected around them.

e. Motors must not be run in series-multiple or multiple series, except on constant-potential systems, and then only by special permission.

f. Motors must be covered with a waterproof cover when not in use, and, if deemed necessary, must be enclosed in approved

cases.

Such enclosures must be readily accessible, dust-proof and sufficiently ventilated to prevent an excessive rise of temperature. Where practicable the sides should be made largely of glass, so that the motor may be always plainly visible.

The use of enclosed type motors is recommended in dusty places, being preferable to wooden boxing.

Where deemed necessary, motors permanently located on wooden floors must be provided with suitable drip pans.

h. Motors must each be provided with a name-plate, giving the maker's name, the capacity in volts and amperes (or watts), and the normal speed in revolutions per minute.

All varying (or variable) speed motors except those used for rail