cable, and where liable to come in contact with gas, water or other metallic piping or other conducting material, wires must be separated therefrom by some continuous and firmly fixed non-conductor creating a permanent separation. Must not come nearer than 2 inches to any other electric lighting, power or signaling wire, not enclosed as above, without being permanently separated therefrom by some continuous and firmly fixed non-conductor. The nonconductor used as a separator must be in addition to the regular insulation on the wires. Where tubes are used they must be securely fastened at the ends to prevent them from moving along the wire.

Deviations from this rule may, when necessary, be allowed by special permission.

f. Wires must be so placed in wet places that an air space will be left between conductors and pipes in crossing, and the former must be run in such a way that they cannot come in contact with the pipe accidentally. Wires should be run over, rather than under, pipes upon which moisture is likely to gather or which, by leaking, might cause trouble on a circuit.

g. The installation of electrical conductors in moulding, or on insulators, in elevator shafts will not be approved, but conductors may be installed in such shafts if encased in approved metal conduits or armored cables.

h. In three wire (not three-phase) systems, the neutral must be of sufficient capacity to carry the maximum current to which it may be subjected.

8417. Underground conductors.—a. Underground conductors must be protected against moisture and mechanical injury where brought into a building, and all combustible material must be kept from the immediate vicinity.

b. Underground conductors must not be so arranged as to shunt the current through a building around any catch-box.

c. Where underground service enters building through tubes, the tubes shall be tightly closed at outlets with asphaltum or other nonconductor, to prevent gases from entering the building through such channels.

d. No underground service from a subway to a building and no service from a private generating plant shall supply more than one building, except by special permission, unless the conductors are properly protected by fuses and are carried outside all the buildings but the one served. Where one or more buildings are supplied from another, the conductors are to be carried outside the buildings. Conductors carried under 2 inches of concrete under a building or buried back of 2 inches of concrete or brick within a wall are considered as lying outside the building. These requirements do not apply to factory yards and factory buildings under single occupancy or management.

$418. Table of allowable carrying capacities of wires.-a. The following table, showing the allowable carrying capacities of copper wires and cables of 98 per cent. conductivity, according to the standard adopted by the American Institute of Electrical Engineers, must be followed in placing interior conductors.

For insulated aluminum wire the safe carrying capacity is 84 per

cent. of that given in the following table for copper wire with the same kind of insulation.

$419. Switches, cut-outs, circuit-breakers, etc.-a. On constantpotential circuits, all service switches and all switches controlling circuits supplying current to motors or heating devices, and all fuses, unless otherwise provided (for exceptions as to switches see §§ 208c, 425a and 443c of this chapter; for exceptions as to cut-outs see § 423, ab of this chapter) must be so arranged that the fuses will protect and

the opening of the switch will disconnect all of the wires; that is, in the two-wire system the two wires, and in the three-wire system the three wires, must be protected by the fuses and disconnected by the operation of the switch.

When installed without other automatic overload protective devices automatic overload circuit breakers must have the poles and trip coils so arranged as to afford complete protection against overloads and short circuits. In two or three phase three-wire circuits, and two-phase four-wire circuits there must be a trip-coil in each of two phases, and in four-wire three-phase circuits there must be a trip-coil in each phase. If a circuit breaker is used in place of the switch it must be so arranged that no one pole can be opened manually without disconnecting all the wires.

This, of course, does not apply to the grounded circuit of street railway systems.

b. Switches, cut-outs and circuit-breakers must, when placed where exposed to mechanical injury or in the immediate vicinity of easily ignitible stuff or where exposed to inflammable gases or dust, or flyings of combustible material, be mounted in approved cut-out boxes or cabinets, except oil switches, circuit breakers and similar devices which have approved casings.

Cabinets and cut-out boxes must be of metal when used with metal conduit, armored cable or metal moulding systems.

In rooms where inflammable gases may exist, particularly in rooms or compartments containing mixing tanks used for the manufacture of inflammable mixtures, in rooms containing wash tanks and in dyeing room of dry cleaning and dry dyeing establishments; in rooms, vaults or compartments used for the storage of inflammable motion-picture films or other nitro-cellulose products, and in cellars or basements used for storage of drugs, all devices which produce or create sparks or arcs must be placed in approved vaporproof enclosures.

c. Switches, cut-outs and circuit-breakers must, when located where exposed to moisture as in basements and similar places, be mounted in approved cut-out boxes or cabinets, and when located in wet places or outside of buildings must be mounted in approved weatherproof cut-out boxes or cabinets.

d. Time switches, sign flashers and similar appliances must be of approved design and enclosed in approved cabinets, except sign flashers mounted as described in § 583b of this chapter.

e. Switches, cut-outs and circuit-breakers must have the spacing within cabinets or cut-out boxes between the walls of the cabinet or cut-out box and current-carrying parts of devices as specified in § 570 of this chapter.

§ 420. Limitation of potential.-The installation in any building, except a central station, or a sub-station, or a transformer vault, of electric light or power wiring or appliances operating at a potential in excess of 750 volts is prohibited.

§ 421. Arc lamps.-Arc lamps must be provided at all times with glass globes surrounding the arc and securely fastened in place. Broken or cracked globes must not be used. Globes must be provided with wire netting having a mesh not exceeding 14 inches. The netting may be omitted where tight inner globes are employed.

§ 423. Automatic cut-outs (fuses and circuit-breakers).— -a. Automatic cut-outs must be placed on all service wires, either overhead or underground, in the nearest accessible place to the point where they enter the building and inside the walls, and arranged to cut off the entire current from the building. Departure from this rule may be authorized only under special permission in writing.

Where the switch required by § 424a of this chapter is inside the building, the cut-out required by this section must be placed so as to protect it, unless the switch is of the knife-blade type and is enclosed in an approved box or cabinet, under which conditions the switch may be placed between the source of the supply and the cut

out.

Automatic cut-outs must not be placed in any permanently grounded service wire.

In risks having private plants, the yard wires running from building to building are not considered as service wires, so that cut-outs would not be required where the wires enter buildings, provided that the next fuse back is small enough to properly protect the wires inside the building in question.

b. Automatic cut-outs must be placed at every point where a change is made in the size of wire, unless the cut-out in the larger wire will protect the smaller (see § 418 of this chapter). This requirement shall not apply to fixture wires and flexible cords connected to branch circuits.

Automatic cut-outs must not be placed in any permanently grounded wire, except as provided in paragraph d of this section.

c. Automatic cut-outs must be in plain sight or enclosed in an approved cabinet, and readily accessible. They must not be placed in the canopies or shells of fixtures.

Link fuses may be used only when mounted on approved bases which, except on switchboards, must be mounted in approved cutout boxes or cabinets. A space of at least two inches must be provided between the open-link fuses and metal, or metal lined walls or metal, metal lined or glass paneled doors of cabinet or cut-out boxes.

d. Automatic cut-outs must be so placed that no set of small motors, small heating devices or incandescent lamps, whether grouped on one fixture or on several fixtures or pendants (nor more than 16 medium base sockets or 25 candelabra base sockets or lamp receptacles) requiring more than 660 watts will be dependent upon one cut-out.

By special permission, in cases where wiring equal in size and insulation to No. 14 B. & S. gage approved rubber-covered wire is carried direct into keyless sockets or receptacles, and where the location of sockets and the receptacles is such as to render unlikely the attachment of flexible cords thereto, the circuits may be so arranged that not more than 1,320 watts (or 32 sockets or lamp receptacles) will be dependent upon the final cut-out.

Except for signs and outline lighting, sockets and lamp receptacles will be considered as requiring not less than 40 watts each if of medium size, or 25 watts if of candelabra size.

All wires of all branches or taps which are directly connected to lamp sockets or other translating devices, must be protected by

proper fuses, except that by special permission in writing fuses may be omitted in grounded wires of such branches or taps.

The above shall also apply to motors, except that 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.

When 1,320 watts are dependent upon one fusible cut-out, as is allowed in theatre wiring, outline lighting, signs and large chandeliers, the fuses may be in accordance with the following table: 125 volts or less.. 125 to 250 volts.

20 amperes 10 amperes

e. The rated capacity of fuses must not exceed the allowable carrying capacity of the wires as given in § 418 of this chapter. Circuit-breakers must not be set more than 30 per cent. above allowable carrying capacity of the wire, unless a fusible cut-out is also installed on the circuit.

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, provided the time limit device is capable of preventing the breaker opening during the starting period.

For the protection of wires having safe carrying capacities exceeding the rated capacity of the largest approved enclosed type fuses, approved enclosed fuses arranged in multiple may be used, provided as few fuses as, possible are used and the fuses are of equal capacity and provided the cut-out terminals are mounted on a single continuous pair of substantial bus bars. The total capacity of the fuses should not exceed the safe carrying capacity of the wires. This does not apply to motor circuits.

f. Each wire of motor circuits except on main. switchboards or when otherwise subject to competent supervision, must be protected by an approved fuse whether automatic overload circuit breakers are installed or not. Single-phase motors may have one side protected by an approved automatic overload circuit-breaker only, if the other side is protected by an approved fuse.

Circuit breakers will be approved for circuits having a maximum capacity greater than that for which approved enclosed fuses are rated.

§ 424. Switches.-a. Switches must be placed on all service wires, either overhead or underground, in the nearest readily accessible place to the point where the wires enter the building, and arranged to cut off the entire current. Departure from this rule may be authorized only under special permission in writing.

Service cut-out and switch must be arranged to cut off current from all devices including meters. Service switches must indicate plainly whether they are open or closed.

In risks having private plants the yard wires running from building to building are not considered as service wires, so that switches would not be required in each building if there are other switches conveniently located on the mains or if the generators are near at hand.