NOTE.-The use of two Standard wires (see page 80), either separate or twin conductor, in a straight conduit installation is approved in the iron-armoured conduit of the Interior Conduit and Insulation Company, but not in any of the other approved conduits. (See Rule 22 e.)]

a. Must be continuous from one junction-box to another, or to fixtures, and must be of material that will resist the fusion of the wire or wires they contain without igniting the conduit.

b. Must not be of such material or construction that the insulation of the conductor will ultimately be injured or destroyed by the elements of the composition.

c. Must be first installed as a complete conduit system, without conductors, strings, or anything for the purpose of drawing in the conductors, and the conductors then to be pushed or fished in. The conductors must not be placed in position until all mechanical work on the building has been, as far as possible, completed.

d. Must not be so placed as to be subject to mechanical injury by saws, chisels, or nails.

e. Must not be supplied with a twin conductor, or two separate conductors in a single tube. (See foregoing note.)

f. Must have all ends closed with good adhesive material, either at junction-boxes or elsewhere, whether such ends are concealed or exposed. Joints must be made airtight and moisture-proof.

g. Conduits must extend at least one inch beyond the finished surface of walls or ceilings until the mortar or other similar material be entirely dry, when the projection may be reduced to half an inch.

A "junction-box" (Fig. 56) is a box made of material similar to that composing the conduit with which it is used, and it is placed where connections are to be made, as, for instance, where a tap wire joins a branch wire or where a branch wire joins a main wire. In these boxes the tubes making up the conduit system end, and from these points all wires are inserted or withdrawn. The use of the junctionbox makes easy the connection of the wires, it brings

FIG. 56.-One form of Junction-box; shown without cover.

these connections to an accessible place, and it provides a receptacle for the fuse-blocks. When these boxes are used it is unnecessary to have concealed joints in the wires and it is possible always to remove lengths of wire that may become defective or that will be too small for an increased number of lights.

Since conduit is allowed in all sorts of places, it should not be of such material that it would burn upon the fusing of the wire. If the wire be prop

erly protected by fuses, it can never overheat sufficiently to melt; but the safety of the construction obviously should not depend upon the carefulness of the men who place the fuses.

As the conduit is not depended upon for insulation, it is doubly important that there be nothing in its composition that will injure the insulation on the wire.

The virtues of the conduit consist in its being a complete protection to the insulation on the wire, entirely enclosing it at all points, and in its affording a smooth and ample raceway for the insertion and extraction of the wires. If conduits were allowed to be installed with the wires inside, there would not be the same necessity to the workman of joining the tubes accurately that there is when the wires must be afterwards inserted, and many installations would, through carelessness, be little better than plain installations of fished wire, with lengths of tube strung along the wire as suited the convenience of the workman. Even if it were allowable to lay strings in the tubes at the time they are placed, so that the wires might be pulled in afterward by means of the strings, there would be danger of abrading the insulation on the wire, because it would then be possible, on account of the force that could be applied, to pull wires through tubes that are too

small, or in which there are obstructions that would tear the insulation. There would be lost, too, all advantage that comes from being able to remove and replace wires with facility. By requiring the conduit to be first installed as a complete system and the wire to be then pushed in, there is assurance that the joints in the tube are well madefor otherwise the wire would catch-and that there are no nails driven through the tube, or obstructions in it, for in these cases the wire could not be forced through.

If conductors are inserted before the mechanical work on the building is completed, any damage to the installation through crushing, cuts, or punctures, not only injures the tubing as a mechanical protection, but it is apt to injure the insulation on the wire at the same place. If the wire is inserted after the work on the building is completed, these damages are likely to be discovered when an attempt is made to insert the wire, and even though the wire slip through easily and the defect in the tubing is not discovered, there is at least the surety that the electrical insulation on the wire is intact.

If a tube containing a twin wire (Fig. 55) or two separate wires, were pierced by a nail and a short circuit thus caused, or if from any other cause an arc were to form in the conduit, there would be

danger of the conduit's igniting before the protecting fuse could melt. With the iron-armoured conduit there is very little liability of such short circuits' forming, because the iron armour is a thick iron pipe like a gas-pipe, and is an effectual protection against nails. Even though an arc form within the conduit, harm could hardly be done, since the fuse protecting the circuit would melt before the iron would be burned through.

Rule 22 (f) is made because it is wished to have the conduit as free from moisture as possible, and by having the ends closed and the joints air-tight there is less liability of the gathering of condensed moisture.

23. Double-pole Safety Cut-outs:

a. Must be in plain sight or enclosed in an approved box, readily accessible.

[Section a. To be approved, boxes must be constructed, and cut-outs arranged, whether in a box or not, so as to obviate any danger of the melted fuse metal's coming in contact with any substance which might be ignited thereby.]

b. Must be placed at every point where a change is made in the size of the wire (unless the cut-out in the larger wire will protect the smaller).

c. Must be supported on bases of non-combustible, insulating, moisture-proof material.

d. Must be supplied with a plug (or other device for