not less than 34 inch in the clear. The wires must be stranded and have approved insulating coverings.

q. Where a socket is not attached to a fixture, the inlet must be provided with an approved insulating bushing which, if threaded, must be not less than 9-32 inch pipe size. The edges of bushings must be rounded and all inside fins removed so that in no case will the cord be subjected to the cutting or wearing action of a sharp edge. Bushings should have holes not less than 9-32 inch in diameter for plain pendant cord, and 13-32 inch in diameter for reinforced cord.

§ 573.

8574. Arc lamps.-a. Arc lamps must be provided with reliable stops to prevent carbons from falling out in case the clamps become loose.

b. All exposed parts must be carefully insulated from the circuit. c. Terminals must be designated to secure a thoroughly good and permanent contact with supply wires, which contact must not become loosened by motion of the lamp during trimming.

§ 575.

8576. Insulating joints.-a. Insulating joints must be made of approved materials both for metal and other parts, including the finishing materials for exterior and interior surfaces. Except for studs designed to be mounted with screws or bolts, they must have a substantial exterior metal casing insulated from both screw connections; they must be threaded in an approved manner; and they must comply with the prescribed tests for heat, leakage, dielectric strength, torsion and bending.

b. Each joint and stud must be marked with the name or trademark of the manufacturer.

§ 577. Fixtures.-a. Fixtures must be made of metal or hard wood, except that other approved material may be used if reinforced by metal or otherwise constructed to secure requisite mechanical strength. In all cases mechanical strength must be secured practically equivalent to an all-metal fixture of similar size and form.

In all fixtures not made entirely of metal, wireways must be metal lined unless approved armored conductors with suitable fittings are used. An exception is made in the case of wireways in glass, marble or similar non-absorptive, non-combustible insulating materials.

All arms must be reliably secured, to prevent turning by threading and soldering, brazing, threading locked by set screw or an equivalent method.

With screw joints of arms and stems there must be not less than five threads all engaging at fixture supports, fixture bodies, etc.

All methods of fastening arms or making joints between metal parts by threading, brazing or otherwise, must be such as to secure in every case ample strength and reliability.

Sockets must, except on pendant cords, be attached to the metal of the fixtures and must be secured in a reliable and permanent manner by threading locked by set-screws or brazing or an equivalent method.

All burrs and fins in wireways must be removed and all sharp edges at points where wires emerge from arms, stems, chains, etc., must, when practicable, be removed or rounded, but in every case

it must be possible to pull in and also to withdraw the wires without injuring them.

Where supply wires enter casings of fixture stems in either straight electric or combination gas and electric fixtures, there must be suitable fittings having smooth, rounded edges to prevent injury to the wire coverings and to prevent the wires from coming into contact with the edges of the ends of casings.

Fixtures for installation outdoors or where exposed to moisture must be so constructed that water cannot enter the wireways, sockets or other electrical parts.

b. Conductors must be not smaller than No. 18 B. & S. gage.

On chains or similar parts where conductors are not completely enclosed in metal, the conductors must be stranded and must have rubber insulation not less than 1-32 inch in thickness. Wires and flexible cords must, when fixtures are externally wired, be so secured as not be to cut or abraded by the pressure of the fastenings or motion of the fixture, and must be protected against abrasion where they pass through sheet metal pans, canopies, etc.

Conductors must be so spliced or joined as to be both mechanically and electrically secure without solder. The joints must then be soldered (unless made with some form of approved splicing device) and covered with an insulation equal to that on the conductors, i. e., with both rubber and friction tape. Wires must, within the arms and stems, be without splices and taps, i. e., it should not be necessary to withdraw the wires to inspect splices and taps.

Receptacles must be so installed as to afford permanent and reliable means to prevent possible turning relative to the surfaces on which they are mounted.

Receptacles having exposed terminals must not be used in canopies unless completely enclosed in metal.

c. Tubing used in threaded arms and stems must not be lighter than No. 18 B. & S. gage. The thickness of unthreaded arms will depend largely upon the method used, and all methods of fastening arms or stems must be such as to secure in every case strength equivalent to that of a threaded connection. Such methods must be submitted for examination, test and approval. Tubing should not be kinked, flattened or cracked.

Canopies must be made sufficiently large, except where outlet boxes are used, to permit the stowing away of splices to fixture leads and to allow supply conductors, and especially the splices to be kept clear of the grounded part of gas pipes.

All methods of fastening arms or stems to fixture supports must be such as to secure in every case strength equivalent to that of a threaded connection.

Conductors used in wiring fixtures must be of approved fixture wire, approved flexible cord, or approved rubber-covered wire, excepting that conductors having approved slow-burning or other heat-resisting coverings must be used in wiring fixtures in which the wiring is exposed, from the heat of lamps to temperatures in excess of 120 degrees Fahr. (49 degrees Centigrade). All such forms of fixtures must be submitted for examination, test and approval before being introduced for use.

All fixtures should, where possible, be sufficiently ventilated to

avoid exposing the wiring to high temperatures, and the wiring of fixtures should be so disposed as to be kept as free as possible from excessive temperatures.

All electrical fittings (including insulating joints, sockets, receptacles, switches, attachment plugs, etc.) must be of approved types.

Canopy insulators must be of approved types. They must be securely fastened in place so as to separate the canopies thoroughly and permanently from the surfaces and outlet boxes from which they are designed to be insulated. A strip of a good grade of hard fibre 1-16 inch thick, permanently attached to the canopy at the ends, and at intermediate points, in such a manner that the strip will permanently extend at least 3-16 inch beyond the entire upper edge of the canopy rim, will be acceptable. Where the above construction is impracticable a sheet of a good grade of hard fibre 1-16 inch thick, permanently attached to the canopy and cut to conform to the general outline of the canopy and with the edges of the sheet at least flush with the edges of the canopy will be acceptable. The insulating strip or sheet must be secured by rivets or screws and the rivets or screws must be so located or countersunk that the desired effective insulation distance is obtained.

d. Tests. Each fixture (after wiring and assembly) must be tested with a magneto which will ring through a resistance of at least 50,000 ohms and show no short circuits between conductors or contacts between conductors and metal parts of fixtures.

e. Markings. Each fixture must be marked with the manufacturer's name or trade-mark.

§ 578. Rheostats, resistance boxes and equalizers.-a. Rheostats, resistance boxes and equalizers must be made entirely of non-combustible materials, except such minor parts as handles, magnet insulation, etc. All segments, lever arms, etc., must be mounted on non-combustible, non-absorptive insulating material. Holes for the supporting screws which secure this material in position must be so located or countersunk that there will be at least one-half inch space, measured over the surface, between the head of the screw or washer and the nearest live metal part.

b. Rheostats, resistance boxes and equalizers must be so constructed that when mounted on a plane surface the casing will make contact with such surfaces only at the points of support. An air space of at least 1-4 inch between the rheostat casing and the supporting surface will be required. The construction throughout must be heavy, rugged and thoroughly workmanlike.

c. Clamps for connecting wires to the terminals must be so designed as to insure a thoroughly good connection and must be sufficiently strong and heavy to withstand hard usage. For currents above 30 amperes, lugs into which the connecting wires may be soldered, or approved solderless connectors, must be used. Clamps or lugs will not be required when leads are provided as a part of the device. d. Rheostats, resistance boxes and equalizers must be plainly marked, where the marking may be readily seen after the device is installed, with the rating and the name of the maker; and the terminals of motor-starting rheostats must be marked to indicate to what part of the circuit each is to be connected, as "line," armature" and "field."

e. The design of the fixed and movable contacts and the resistance in each section must be such as to secure the least tendency toward arcing and roughening of the contacts, even with careless handling or the presence of dirt. In motor-starting rheostats, the contact at which the circuit is broken by the lever arm when moving from the running to the starting position must be so designed that there will be no detrimental arcing. The final contact, if any, on which the arm is brought to rest in the starting position must have no electrical connection.

f. Motor-starting rheostats must be so designed that the contact arm cannot be left on intermediate segments, and for direct current circuits must be provided with an automatic device which will interrupt the supply circuit before the speed of the motor falls to less than 1/3 of its normal value. In motor-starting rheostats for alternating current circuits the automatic, interrupting device may be omitted.

g. Overload-release devices which are inoperative during the process of starting a motor will not be approved, unless other circuit breakers or fuses are installed in connection with them.

§ 579. Auto-starters.-a. Coils and switches of auto-starters used in dusty and linty places or where exposed to flyings of combustible material, must be completely enclosed in substantial metal cases so constructed as to effectually exclude ordinary dust, lint or flyings of combustible material.

Auto-starters used in places where the above conditions do not exist, may be of any approved type. Cases for either transformer coils or switches must provide for access to the interior for inspection and for renewal of oil, and must be so constructed that when mounted on a plane surface the casing will make contact with such surface only at points of support. An air space of at least 4 inch between the casing and supporting surface will be required. The oil tank shall be marked in a suitable manner to indicate the proper oil level. When such device carries a visual oil indicator, the marking shall be for the proper oil level with the starter assembled. If the visual indicator is not used, markings shall indicate the oil level prior to assembling. The switch must provide an off position, a running. position and at least one starting position. It must be so arranged that it will be held in off and running positions but cannot be left in a starting position or without the proper running over-load protective devices in the circuit. The construction throughout must be thoroughly substantial.

b. Clamps for connecting wires to the terminals must be so designed as to insure a thoroughly good connection and must be sufficiently strong and heavy to withstand hard usage. For currents above 30 amperes, lugs into which the connecting wires may be soldered, or approved solderless connectors, must be used. Clamps or lugs will not be required when leads are provided as a part of the device.

c. Auto-starters must be plainly marked, where the marking may be readily seen after the device is installed, with the rating and name of the maker; terminals to be so marked as to indicate to what part of the circuit each is to be connected.

§ 580. Reactive coils and condensers.- -a. Reactive coils must be

made of non-combustible material, mounted on non-combustible bases and treated, in general, as sources of heat.

b. Condensers must be treated like other apparatus operating with equivalent voltage and currents. They must have non-combustible cases and supports, and must be isolated from all combustible materials and, in general, treated as sources of heat.

§ 581. Transformers, low potential. 1. Air cooled transformers.— a. Air cooled transformers must be placed in substantial metallic or other non-combustible cases, which completely enclose all currentcarrying parts, with the exception of the terminals of the low voltage windings as specified below. Sheet metal cases must be not less than 1-32 inch in thickness, and cast iron must be not less than 1-8 inch in thickness. Such transformers must be so constructed that when mounted on a plane surface the casing will make contact with such surface only at the points of support. An air space of at least onefourth of an inch between the transformer casing and the supporting surface will be required.

Leads of approved cable at least 6 inches in length and so secured as to prevent strain coming on the connections to the coils, must be brought out of the case through approved insulating bushings, except for bell-ringing and toy transformers, the low voltage terminals of which may be binding posts mounted on the case.

The construction throughout must be substantial and thoroughly workmanlike.

b. Air cooled transformers must be plainly marked, where the marking will be readily seen after the transformer is installed, with the name of maker, with the frequency, the high voltage and all low voltages, and the rated capacity in kilo-volt-amperes.

2. Bell ringing or other signaling transformers. d. Transformers for bell-ringing or other signaling service only must be constructed in accordance with the requirements of paragraph a of this section, and may be approved for use when all wiring on the high voltage side is in accordance with the requirements of article 4 of this chap

ter.

e. Such transformers must be plainly marked where it can be seen after installation, with the name of the manufacturer, the frequency, the high voltage and all low voltages, and the proper terminals must be marked "Line" and "Bell." The rating of high voltage winding must not be over 125 volts.

f. The design of the transformer must be such that when any two low voltage terminals are short circuited while the rated voltage is impressed on the high voltage coil, the input measured by a wattmeter in the high voltage circuit will not be more than 25 watts.

3. Toy transformers. g. Transformers for operating toys must be constructed in accordance with the requirements of paragraph a of this section.

h. Such transformers must be marked with the name of the manufacturer, high and all low voltages, the frequency and the rated capacity in volt-amperes.

The high voltage rating must not exceed 125 volts, nor the low voltage rating exceed 25 volts.

i. Such transformers must be so constructed as to stand the following test: