Fig. 2. Flexible Steel Conduit.

Courtesy of Sterling Electric O., Troy, N.Y.

Table V. Greenfield Flexible Steel Conduit

Inside Diameter

Outside Diameter

5/16 inch

200

3/8 "

200

1/2 "

100

3/4 "

50

1 "

50

1 1/4 "

50

1 1/2 "

50

2 "

Random Lengths

2 1/2 "

" "

3 "

" "

This conduit should, of course, be first installed without the conductors, 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, considerable difficulty will be experienced in drawing the conductors in the conduit.

The rules governing the installation 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, the 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, probbably the next best results may be obtained by the use of steel armored cable. The rules governing 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. Dare 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 manufacture, 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-conductor cable, from No. 10 to No. 14 B. & S. G. Table VI gives various data relating to armored conductors:

Fig. 3. Use of Elbow Clamp for Fastening Flex ible Conduit in Place.

Fig. 3. Use of Elbow Clamp for Fastening Flex ible Conduit in Place.

Fig. 4. A 100 Foot Coil of Flexible Steel Conduit. Courtesy of Sprague Electric Co., New York, N.Y.

Fig. 4. A 100-Foot Coil of Flexible Steel Conduit. Courtesy of Sprague Electric Co., New York, N.Y.

Fig. 5. Outlet box for Flexible Seel Conduit.

Fig. 5. Outlet box for Flexible Seel Conduit.

Fig. 6. Outlet Plate for Flexible Steel

Fig. 6. Outlet Plate for Flexible Steel Conduit.

Fig. 7. Outlet Bushing.

Fig. 7. Outlet Bushing.

Courtesy of Sprague Electric Co., New York, N. Y.

Fig. 8. Flexible Armored Cable. Twin Conductors.

Fig. 8. Flexible Armored Cable. Twin Conductors.

Courtesy of Sprague Electric Co., New York, N.Y.

Table VI. Armored Conductors - Types, Dimensions, Etc

Size B.&S Gauge

Type and Number of Conductors

Outside Diameter

(Inches)

No. 14

BX twin conductor

.63

" 12

" " "

.685

" 10

" " "

.725

" 8

" " "

.875

" 6

" " "

1.3125

" 14

BM twin conductor (for marine work - ship wiring)

.725

" 12

" " "

.725

" 10

" " "

.73

" 14

BX3 three conductor

.71

" 12

" " "

.725

" 10

" " "

.73

" 14

BXL twin conductor, leaded

.725

" 12

" " " "

.725

" 10

" " " "

.87

" 14

BXL3 three conductor, leaded

.90

" 12

" " " "

.90

" 10

" " " "

.94

" 10

Type D single conductor, stranded

.550

" 8

" " " " "

.550

" 6

" " " " "

.575

" 4

" " " " "

.700

" 2

" " " " "

.900

" 1

" " " " "

.965

" 10

Type DL single conductor, stranded, leaded

.625

" 8

" " " " " "

.710

" 6

" " " " " "

.700

" 4

" " " " " "

.760

" 2

" " " " " "

.920

" 1

" " " " " "

.910

Steel Armored Flexible Cord

" 18

Type E twin conductor

.40

" 16

" " "

.40

" 14

" " " "

.47

" 18

Type EM twin conductor, re-inforced

.575

" 16

" " " " " "

.585

" 14

" " " " "

.595

In Table VI, Types D (single), BX (twin), and BX3 (3 conductors) are armored cable adapted for ordinary indoor work. Type BM (twin conductors) is adapted for marine wiring Type 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 suitable 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 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.