General Rules are Given in New Fiber-optic Box Installation Standard


The first requirement is that, "All fiber optic box should be installed in accordance with their listings and manufacturers' instructions." Obviously. But the support section gives precise details on how cables must be supported: All optical cables shall be securely supported, and shall have the supports spaced closely enough that there will be no excessive force placed on the cable. In general, horizontal indoor cables shall be supported at intervals not exceeding 3 ft (91 cm). Supports may be placed up to 5 ft (1.52 m) apart for armored cables, or cables more than 1/2 in. (1.3 cm) in diameter. Cables directly buried require no additional support. Cables in raceways are considered to be adequately supported by the raceway.

Another important section is concerned with the tightness of supports. With power wiring, we are seldom concerned with supports being over-tightened, but with data cables (not only fiber), over-tightening is a frequent source of cable damage, and must be avoided. The section reads as follows:

"All straps or supports placed on fiber-optic cables shall be tight enough to hold the cable securely, but shall not be tight enough to substantially deform the shape of the cable. Where possible, rounded or padded supports shall be used. Cable ties shall not be cinched too tightly, and shall have the free tab cut off, to prevent over-tightening in the future."

The standard also gives general rules to be followed when pulling cables into place. After mentioning that manufacturer's instructions take pre-eminence, the following general rules are given:

1. When pulling optical cables into conduits, cable trays, or raceways, the strength member(s) of the cable shall bear all or nearly all of the pulling force. Cable jackets shall not be directly pulled unless designed for the purpose, or unless the run is very short and requires a minimal pulling force. Optical cables shall not be pulled into place by applying tension directly to the fibers (pulling the fibers).

2. Optical cables shall be attached to a pulling line only by methods recommended by the manufacturer of the cable.

3. Unless stated otherwise by the cable manufacturer, the maximum pulling tensions used for optical cables shall be 300 lbs. (136 kG) for multi-fiber indoor cables, and 600 (273 kG) lbs. for outdoor cables. The pulling force shall be uniform and consistent; cables shall not be jerked.

4. Cable pulling shall be done by hand, except when tension meters, tension-controlled or break-away swivels are used.

5. When powered pulling equipment is used to install optical cable, tension monitoring equipment or break-away swivels shall be used. Swivels shall be used when pulling optical cables into conduits. Exceptions shall be made to this requirement only for very short runs which require a minimum pulling force.

6. Continuous cable pulls shall be used whenever possible, avoiding splice points.

7. Boxes used with optical cables shall be designed for the purpose, and shall be equipped with cable supports. Pull boxes shall be sized so that no cables in the box shall be tightly.