Table V gives the inside diameter of various sizes of flexible con duit, and the lengths of standard coils. inside diameter of this conduit is the same as that of the rigid conduit; and the table given for the maximum sizes of conductors which may be installed in the various sizes of conduits, may be used also for flexible steel conduits, except that, a little more margin should be allowed for flexible steel conduits than for the rigid conduits, as the stiffness of the latter makes it possible to pull in slightly larger sized conductors.
This conduit should, of course, be first installed without the con ductors, in the same manner as the rigid conduit. Owing to the flexibility of this conduit, however, it is absolutely essential to fasten it securely at all elbows, bends, or offsets; for, if this is not done, con siderable difficulty will be ex perienced in drawing the con ductors in the conduit.
The rules governing the in stallation of this conduit are the same as those covering rigid conduits. Double-braided conductors are required, and the conduit should be grounded as required by the Code Rules. As already stated, thc conduit should • be securely fastened (in not less than three places) at all elbows; or else the special elbow clamp made for this purpose, shown in Fig. 3, should be used.
In order to cut flexible steel conduit properly, a fine hack saw should be employed. Outlet-boxes are required at all outlets, as well as bushing and wires to rigid conduit. Fig. 4 shows a coil of flexible steel conduit. Figs.
5, 6, and 7 show, respectively, an outlet box and cover, outlet plate, and bushing used for this conduit.
Armored Cable. There are many cases where it is impossible to install a conduit system. In such cases, prob bably the next best results may be obtained by the use of steel armored cable. The rules gov erning the installation of armored cable are given in the National Electric Code, under Section 24-A, and Section 48; also in 24—S. This cable is shown in Fig. 8.
Steel armored cable is made by winding formed steel strips over the insulated conductors. The steel strips are similar to those used for the steel conduit. Care is taken in forming the cable, to avoid crushing or abraiding the insulation on the conductors as the steel strips are fed and formed over the same. In the process of ture, the spools of steel ribbon are of irregular length, and when a spool is empty, the machine is stopped, and the ribbon is started on the next spool, the process being continued. There is no reason why
the conduit cables could not be made of any length; but their actual lengths as made are determined by convenience in handling. Armored cable is made in single conductors from No. 1 to No. 10 B. & S. G.; in twin conductors, from No. 6 to No.14 B. & S. G.; and three-conduo tor cable, from No. 10 to No. 14 B. & S. G. Table VI gives various data relating to armored conductors: tors) are armored cable adapted for ordinary indoor work. Type BM (twin conductors) is adapted for marine wiring. Types DL (single), BXL (twin), and BXL 3 (3 conductors) have the conductors lead-encased, with the steel armor outside, and are especially adapted for damp places, such as breweries, stables, and similar places.
Type E is used for flexible-cord pendants, and is suitable for factories, mills, show windows, and other similar places. Type EM is the same as Type E; but the flexible cord is reinforced, and is suit able for marine work, for use in damp places, and in all cases where it will be subject to very rough handling.
While this form of wiring has not the advantage of the conduit system—namely, that the wires can be withdrawn and new wires inserted without disturbing the building in any way whatever—yet it has many of the advantages of the flexible steel conduit, and it has some additional advantages of its own. For example, in a building already erected, this cable can be fished between the floors and in the partition walls, where it would be impossible to install either rigid conduit or flexible steel conduit without disturbing the floors or walls to an extent that would be objectionable.
Armored conductors should be continuous from outlet to outlet, without being spliced and installed on the loop system. Outlet boxes should be installed at all outlets, although, where this is impossible, outlet plates may be used under certain conditions. Clamps should be provided at all outlets, switch-boxes, junction-boxes, etc., to hold the cable in place, and also to serve as a means of grounding the steel sheathing.
Armored cable is less expensive than the rigid conduit or the flexible steel conduit, but more expensive than cleat wiring or knob and tube wiring, and is strongly recommended in preference to the latter.